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MG Midget and Sprite Technical - Torque dry or with oil?
| Looking for information about high tensile bolt grades on the web, I have come across some engineering websites that tell you bolts should be torqued to spec dry, without lubrication. I have always taken for granted they should be lubed with motor oil before they are torqued to factory specs. Except ARP, of course, with their special lube. What do you do? |
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| Boltbabble or Lubrication and Threaded Fasteners and Torque To Yield Bolts, Savior or Scam? and Head Gaskets, Road Wheels, and Other Bits You Don't Want Falling Off and British Threads & Tools 15 March 07 I wrote this some time ago, but it struck me that I should introduce myself and tell how I got to the point of relating the following, so here goes. It is said that before I could walk, I crawled about with my father’s tools, taking stuff apart. At age 3, I meticulously filled all the chips and holes in the old plaster where we lived, with toothpaste! From then up to leaving home at 18, I hung around with old time real German and Pennsylvania “Dutch” = German mechanics and machinists, racecar shops, and the like. Meanwhile, my father bought a brand new Morris Minor in 1950, followed by an Austin A40 Devon, then a succession of Chevrolets and finally flathead Fords and a Morgan. There was a steam car (1913 Stanley works in a 1931 Chevrolet coupe cum roadster) around age 10, which I fixed and operated. I cleared land by hand, with weapons no kid would be allowed to touch today, fixed pipes, buildings, lawnmowers, and anything else that moved and broke. I was the town champion bicycle rider on my scrapyard special; I would challenge all comers to race me, and most never returned. My first car was a 1947 Ford, slightly modified. The tires cost about $8 each from Sears, and nothing could stay with me on a twisty road. After a bit of engineering school, I started as a British car mechanic in 1966, and have been doing that for half the time since, including working in, operating, or owning a number of the biggest independent Britcar shops in Pittsburgh from 1966 to 75. Then I moved to the country, where things are more sporadic but less hectic, so I spend a lot of time figuring out how things really work – or don't. The rest of my time has been spent running a big truck, building machinery, and most relevantly, seriously studying mechanics. 95% of my 2 and 4 wheeled vehicles have been British – all the good ones, except the current 92 Mazda 323, a stone reliable Japanese version of a BMC1100/1300 with power! Most of these cars were built out of junkyard refugees at the lowest dollar amount possible, since the only thing I can’t do is make money. Around age 15, c.1962, a family friend came to visit in his Mercedes 1954 180D, bought new in Germany, showing around 200,000 miles. It had blown a head gasket, replaced by the dealer. Blew again, and he was sorely distressed, since he knew it shouldn’t. He was stuck at our house, so I asked if they had retorqued the head, and he said that the dealer said it was unnecessary. I tapped into the real mechanics network, and every one said, “You know damn well that any thick gasket thing needs to be retorqued, and it don’t matter what the book says. That’s how it’s done”. So, I changed the gasket, got it hot, and retorqued it. Ran it 100 miles and did it again. He went off for a week and 1000 miles, and stopped back; we retorqued again. I told him what the graybeards told me, “Retorque every two years”. I lost touch and I’m sure he and the car are both long gone, but I’m sure he did that, since he was in love with the car and expected it to last as long as he did. Last I heard it had 500,000 miles with no further problem. Enough intro, already. FRM Friction and Lubrication on Threaded Fasteners There has been much discussion in automotive circles regarding torque specifications and the use of lubricants on critical threaded fasteners such as road wheel lug nuts and cylinder head nuts. I find that it is generally incomplete, frequently incorrect, and sometimes dangerous to man and/or machine. Usually statements can be seen to be based on some specific information in the distant past, which are now divorced from their original and usually very specific circumstances. The fundamental problem is that torque specs are rather a “quick and dirty” method of informing us of the clamping loads in the assembly, which is accurately measured by stretch in the given fastener. This is usually difficult or impossible to measure at all, and time consuming and finicky if possible. It is sometimes done in cases where loading must be very accurate and both ends of the fastener are accessible for measurement, as in high performance con rods; in this case the bolt length can be measured with a micrometer. Another approach is to tension the assembly with a known load to a calculated “stretch”, usually hydraulically, a method used on things like large turbine shaft assemblies; in this case one nut may retain several tons and a million dollars worth of bits, all spinning at extremely high speed.. Given a particular fastener, clamp loads based on fastener torque can be calculated nicely in theory, IF you disregard friction. It turns out that friction is a very major and unpredictable factor though, and absorbs a good deal of the effort of tightening, leaving actual clamp loads unacceptably low and variable. It is therefore necessary to indulge in the art of correction factors; it is not very hard to arrive at a suitable factor by experiment for a particular situation. It cannot be emphasized enough that the factor is only correct for that exact situation; this includes such things as material of all frictional surfaces, the finish and heat treatment of said surfaces, all lubricants and contaminants present -- they may be one and the same or contradictory -- and even variables like the number of times a fastener has been used and the speed of tightening. Thus we arrive at the true “black art”: friction control. It involves mysterious unguents derived from plant and beast, alchemical preparations of elements, physical massaging of parts, incantations and misdirection, fire, earth, air, and water. I will deal with each to some extent, but it is by no means exhaustive. Physical Characteristics The first rule of material selection is that, with the exception of grey cast iron, almost NO material is satisfactory as a load carrying bearing against itself; the two materials must be different. (Grey CI has free graphite in it, which is discussed later.) If not, when under load the microscopic high spots which make contact will get confused as to which piece they belong to and will transfer back and forth at random. If the situation is not too severe, this is called galling; very severe cases are known as friction welds and are in fact used in the production of parts. In some cases, differing materials will still do this; in other cases, the only needed difference is that one piece be in a different physical state due to heat treatment or cold work. As an experiment, obtain some cheap bolts and nuts from the local discount store. You want the unplated plain steel kind. Clean thoroughly with acetone or lacquer thinner, making sure there is no oil on them. Tighten them up very firmly on a spacer and back off a few times. After several cycles in succession you will have worn or broken through the thin oxide layer and you will find that they get very “sticky”. Examination under magnification will reveal that the threads are rough and torn - galling. Material condition in this context is primarily a matter of the surface; it must be remembered however, that if you successfully reduce friction enough you may obtain high enough stresses to break the fastener or shear the threads. Smooth surfaces reduce the local contact forces by distributing the load over more tiny contact points. This is a benefit to the use of rolled thread fasteners, in addition to the more favorable stress factors of a smooth surface, and good grain flow in the fastener body. The rolled thread also creates a much harder surface by cold work; a rolled male piece with a cut female may be sufficient difference to prevent galling at fairly low load. Note that it is poor practice to chase the threads of rolled fasteners for cleanup – doing so with a normal tap or die notches the root radius and negates much of the benefit of the rolled thread. An excessively smooth surface may not be desirable either, as it provides no pockets for lubricants, allowing the same intimate contact. High material hardness at the nut/washer interface is desirable; soft material allows deformation, leading to high local stresses, leading again to galling. I have seen a lot of this in obviously overtightened/unlubricated fasteners. With your cheap bolts from above, drill a rather oversized hole in something, as a 1/2-9/16 hole for a 5/16-or3/8 bolt. Put unplated washers under the nut and tighten. The washer will dish in, giving high stress contact at the inside edges of the hole, which will gall. Case hardened washers which are too thin will dish as well, giving sharp-edged surface cracks which cut the nut; this is distinct from galling, which is prevented by the hard surface. Lubricants In the broadest sense, lubricants are anything that prevents the direct contact of the actual material of the fastener parts from touching each other or the clamped parts involved. These may include both naturally occurring and intentionally produced solid coatings, as well as the salves we usually think of. Natural coatings are usually oxides, as in aluminum, stainless steel, and even common rust on plain steel. While they are usually very hard, they tend to be thin and brittle, so are not durable under heavy loads in threaded fasteners. Stainless forms a very nice oxide, which is why it is “stainless”, but most grades gall severely in threaded applications unless an anti-seize compound is used. Take 2 pieces of aluminum and sand thoroughly with 400 silicon carbide paper and water. Quickly dry and rub the two pieces together with moderate pressure. You should get galling pretty quickly, since you have destroyed the oxide layer by sanding. It reforms quickly though; after a few hours you can rub them together without galling, under much more pressure. The extension of this is a process like Magnaplate, where the aluminum is anode-oxidised (anodised) to a very thick oxide layer and then impregnated with teflon or similar. It is not possible to remove this coating with a file, and nearly impossible with a grinder, and it is exceedingly slippery. Similar treatment can be done on many metals. Other coatings, which are chemically oxidation products, include phosphate, chromate, and plain oxides produced by heat or chemicals. Black oxide on steel is more or less a by-product of heat treatment, often encouraged because it is a good anti-seize surface, though it needs additional protection with oil or wax. Parkerizing is basically a zinc-phosphate treatment, though it has some secret ingredients to help it along. All of these tend to prevent rust, being already oxides; most are actually somewhat rough and/or porous, and are used with an additional wax or oil coating filling the roughness. Many of these coatings also involve other metals, further separating the steel of the fasteners. Some of these coatings have characteristic colors; many are dyed for identification. Metallic platings function as anti-seize coating/lubricants in addition to being rust-preventive and decorative. Zinc is most common; nickel, copper, cadmium, lead, tin, and silver are all used. There are solid synthetic coatings, such as resins, plastics, and specially formulated lacquers and paints. Finally, we get to “lubricants” as we normally think of them. They serve the purpose of separating the metallic surfaces and sometimes act as coolants. This is the real witchcraft. Mineral oil is the usual sort; it is fossil hydrocarbons. More recent decedents supply sperm oil, tallow, lard oil, etc. Waxes come from plant sources, insects, and various sea creatures, as well as from the aforesaid fossil hydrocarbons. Many of these compounds have analogues in which the carbon atoms are replaced by silicon. There are further synthetic analogues, and totally new synthetics as well. Sometimes they are solid, as polyethylene and the flourocarbon known generally as Teflon. Greases are oils held in a thickener, so that they don’t run away; the thickener is designed to meter the oil feed to the part. The thickener is usually a lithium, calcium, or sodium based soap; this may contribute its own anti-seize properties. Greases may be further modified by the addition of other anti-seize and anti-corrosion elements, like lead, molybdenum disulphide, Teflon, polyethylene, or graphite. Lubricants are designed and compounded by engineers, with great attention to the specific conditions of operation. They use all the above components and more. Once they reach the commercial stage, marketing takes over with the intent of selling the product and keeping the engineers’ work as a trade secret. In the process, a lot of application information and most of the compounding is lost or obscured. The process continues when users say, “use this”, while not understanding or specifying the engineer’s intent, or the exact product. In particular, most brand names cover a range of products; some are or have become generic. Failure to specify which “Lubriplate” or “Anti-Seize” leads to confusion and mis-application. Anti-Seize is a generic term, a brand name, and a product name within other brand names. The original A-S was a grease containing metallic lead particles; it is largely superseded as a result of the anti lead movement but is still available. The most common forms on today’s shelves are light greases containing some or all of graphite, aluminum, copper, nickel, and stainless steel powders; the G-A-C form is most prevalent. Others are used for certain purposes: G-N without A for high temperatures, G-SS for extreme temps, no copper for radiation service, etc. Most contain graphite, and almost any are suitable for the purposes of general use. There are occasional chemical issues, like not using graphite on aluminum (although the presence of oil seems to prevent problems), or corrosion of bronzes by some extreme pressure lubes. Penetrants are for seeping into tight or corroded fastenings, which were assembled without suitable lubrication. They are usually petroleum based, but water is helpful on plain rust, and sulphuric acid works for acid-corroded joints. They both act as solvents since the corrosion took place in that solution. Before the advent of commercial penetrants, turpentine was used extensively, and oil of wintergreen (methyl salicylate) is an old time Mechanic’s remedy. Applications At last, the point of it all! General references on torque for generic fasteners are approximate in the extreme, while sounding definitive. You will normally get something like “For grade X, of size Y, tighten to Z. Reduce 10% if lubricated.” Sometimes, “If anti-seize (or graphite or Moly) is used, reduce torque 20%.” The only parameters are those intrinsic to the grade of fastener, if that is mentioned. Surface treatments like plating, and things like what kind of lubricant don’t show up. References from bolt manufacturers do better, especially those who make a wide range of fasteners. OEM references can be quite good, if they mention the presumed state of lubrication, which they frequently do not do. They always are based on the material/finish as supplied for the application; this is not usually specified and must be determined by examination. If you can identify these characteristics, then you are on your way to understanding the subject in a generally useful way. You can get to the point where you are able to identify quirky specs resulting from design peculiarities, and generalise to a range of likely torques for other, similar, apps. While it will not be as good as correct specific specifications, you probably won’t damage things, nor will they fall apart immediately. As a rule, I find that any reasonably heavily loaded “dry” spec. indicates that there is a surface treatment present, as it would gall otherwise. This is effectively a dry anti-seize; the friction will usually be higher than it would be with a “wet” A-S. I would reduce torque by 10% for use of normal A-S on a dry spec fastener. Virtually all high load fasteners do have surface treatments and good finish, so if it is specified as “oiled”, you are reasonably safe in using an anti-seize at that torque; go for minus 5 to 10% if you are fairly sure that there is no surface treatment. If they give a torque range of 10 to 20% of the high figure, use A-S at the low spec. On extremely critical things like con rod bolts, make every effort to obtain the factory specs, preferably from the fastener manufacturer if not OEM. Some applications specify two or more tightenings, fasteners being backed off in between. I have encountered a number of engines, which call for this on crankshaft bearings. The procedure is to tighten incrementally in some sequence, back off in a reverse sequence until they are a turn or two loose. Without disturbing the parts otherwise, repeat the whole process. The point is to allow the parts to seat with no extraneous stresses; I have adopted this for all crankshaft installations, mains and rods. In other cases, as in ARP high performance studs, it is specified to tighten and loosen in sequence for 5 or more cycles. In this case, you are “wearing in” the surface finish to a predictable state, in order to give accurate torque readings. I have tried this on cylinder heads; it does result in more stable results on the second cycle, but is no great improvement on my usual procedure (below). In general the life history of the fastener has a lot to do with performance. Galled threads mean Replace!, threads that have been tightened a number of times with good lubrication bed in nicely and give good results. If an A-S was used previously, you can get by with no lube for one or two additional tightenings; enough A-S is bonded to the metal to do the job, even if the bolt is thought to be “clean and dry”. Surface coatings improve for the first few tightenings, then eventually wear out, especially if not lubricated. Bolts cleaned on wire wheel brushes should be treated as having no surface treatment, since the wheel probably has removed or broken surface coatings. Fatigue failure of fasteners is a serious matter. Any fastener which fails after fairly long service is fatigued. This results from tensile loads cycling from high to low, or a change in direction of bending loads. Assuming the clamped parts are reasonably rigid, the reason for the cycling is that the fastener is actually looser than required to maintain a constant high stress in the assembly. A salesman once showed up, selling an anti-seize or extreme pressure lubricant. I demanded documentation of his claims - wonder of wonders, he came back with case studies. In a small high performance engine application, con rod bolt breakage and fallout, and rod breakage, had resulted in an ongoing trek through increased torque, better bolts etc. Over a several year period, this resulted in some improvement but still random failures occurred at unacceptable levels; costs were very high. When they began using the A-S, they were able to return to the original bolts and torque specs, with no subsequent failures. The explanation was that the bolts were in fact being tightened to widely varying applied stresses, despite constant and careful torque settings, surface treatments, and in some tests, the use of oil as a lube.. The loosening was clearly a result of too loose conditions, but the fatigue and breakage were also a direct result of insufficient clamp load in the assembly as a result of erratic friction in the threads. The high strength, high torque bolts suffered the same malady, but also distorted the rod and screwed up bearing clearances. The original engineers had done a perfect job of stress calculations, except for the erratic frictional characteristics. A BMW motorcycle manual of standard torques states: “1.) For “normal” bolts: bolts phosphate treated, nuts without after-treatment, or galvanized. Lubricated condition: non-lubricated or oiled; 2.) For their “normal” self locking nuts: Surface condition: bolt phosphate treated or galvanized, nut galvanized and not waxed. Lubricated condition of bolt: either non-lubricated or oiled. For cadmium plated bolts or nuts: reduce torque approx. 30%.” Note that cadmium plate was formerly used extensively and is extremely good for the task; it has however been largely superseded due to environmental and exposure concerns. A number of early British bikes, such as Royal Enfield, used cad-plated fasteners and give what seem to be very low torque specs as a result. Cylinder heads Cylinder heads and other thick-gasket applications call for incremental and sequential tightening. In this case, time at pressure is extremely important, as are the number and degree of heat-cool cycles. The gaskets “flow” under pressure, with time. Mileage is often used, but is meaningless except as a rough indicator of these factors. These applications normally require retorque at later dates. While there is increasing use of “no-retorque” gaskets and a lot of controversy on the subject, my experience is that properly done retorques never hurt, and frequently show movement that indicates looseness of the head bolts, even on the no-retorque engines. Loose head bolts will always eventually cause blown gaskets. The need for retorques means that durable lubricants must be used in assembly. Surface coatings will wear out over numerous tightenings; oil will squish out. If nuts seize or drag excessively on retorques, then the nuts must be removed to relube. This is best avoided; if needed it can be done by loosening the head in reverse sequence to a low figure but still snug, so as not to break the existing seal. Typically, I loosen to something like 20 lbft, then removing one nut at a time, applying anti-seize, and retorquing as new. I have done it a number of times; I always am ready for failure, but never had one yet. Use anti-seize on initial assembly! ******************* Following is a discussion with Paul Hunt re MGB headgasket problems, rearranged from the MG board. Paul: The shims {FRM note: two thin shims fitted under the two center rocker stands on later MGB} are there to put a very slight bend *in* the shaft, or more correctly make sure it is held stiffly by putting the four mounts very slightly out of line, so it can't itself twist back and fore which wears its mounts. They should be refitted, it was issued as a mod to earlier engines that didn't have them originally, to be applied when the rocker shaft was removed for other reasons. FRM: Paul is correct on the rocker shims. Paul: I thought copper *was* the original material - on the 4-cylinder at any rate. Mine is, although it is a gold-seal engine which may have been rebuilt. FRM: "Copper" can be misleading. The OE gasket on early cars was asbestos faced with copper on one side, and either steel or copper colored to look like steel on the other. They work very well if correctly installed and retorqued. A bit of looking will turn these gaskets up - Clough & Wood make them in the UK, and TRF sells them here. These gaskets seem to be referred to as "copper"; it would be less confusing and more accurate to call them "copper faced composite". These come from the factory with an appropriate resin seal coat – no other sealant should be used. There are solid copper gaskets, also called "copper". It is an old racer trick used for expedience, quick head changes, compression changes, and lack of a "real" gasket. They work fine if done right, but only for a short time, after which they leak, but rarely fail totally - good for racecars. These have no resilience to accommodate heat/cool cycles, so they are not very good for street use. The hucksters sell them as "competition upgrades" - "...a secret ingredient of many high performance racing engines" Gets the suckers every time! And after the thing leaks, then they get to sell more gaskets, "upgrade" or "Regular" or "Premium" - or all of the above, since NOBODY seems to know how to do it correctly anymore. Finally we have the Payen or similar resin faced fibre gasket. It lasts longer without retorque than the copper faced ones, but will invariably leak after a while. And it is a PITA to get off the block and head when it dies. The Payen gasket, installed correctly, will get the car well past warranty period with a little luck, even without retorque, but it will fail eventually. In situations where the gasket has not been in use too long, the copper faced gasket can be reused by cleaning and a thin coat of Permatex #2 sealer, though it's not "good practice"; you ain't a'gonna do that with a Payen. Paul: Should be head studs and nuts - again on the 4-cylinder, and therefore can't be too long - unless they have stretched so much the end of the threads is above the top of the head! Stretching *is* an issue with bolts, as they can bottom in the block holes before applying full torque to the gasket, but as I say that shouldn't apply to the 4-cylinder. {FRM note:"stretching" here is used to indicate that the bolt or stud is too long to clamp the head properly, which is also the case if a lot of material has been machined off the head or block. Check that stud threads do not end above the top head surface before installing the correct washers. This will ensure adequate clamping. Bolts or studs that are actually stretched, commonly visible at the coarse threaded end, must be replaced. I've seen a few, but never on a BMC A or B series engine.} Paul: The seal between 2 and 3 can be problematical as it is so narrow. FRM: Not if the head is torqued correctly. Paul: John Twist writes this "MGB WEEPING CYLINDER HEAD: The rule is, all rebuilt B series engines weep between the block and head, between the 2nd and 3rd spark plug. Some actually piss. To remedy this problem: That center exposed head stud, RH side, between #2 and #3 is the guide stud -- the hole in the head is 3/8 whereas the other holes are 7/16. Clean out the stud hole in the head with a 3/8 drill. Polish that stud, at least. Ensure a chamfer at the threaded hole in the block. Chase the threads on the stud, nut, and block (3/8-16 and 3/8-24) {FRM note: It's not really good to chase the stud threads, as they are usually rolled and chasing cuts through the radius at the bottom of the V, weakening the thread. Replace them if the threads are damaged.}. Ensure the head is planed to 0.001." Ensure that the top of the block is cleaned to a SMOOTH finish. Fit the studs back into the block with only about 5 lb-ft torque. Place a THIN film of clear silicone, RTV, sealant on the RH side of the head gasket. Into that EXTREMELY THIN film, place two strands of stranded, flexible wire about six inches long, twisted together, along the outboard side of the gasket, between its edge and the water jacket holes so that the thickness of the head gasket is effectively increased by several thousandths. Goodbye leaks." FRM: I am quite surprised and disappointed by Paul's quote from John Twist on seepage and the cure thereof. NONE of my rebuilt/repaired/patched together engines seep, leak, or blow gaskets, EVER, in 40+ years. And I don't go through all that rigmarole either. The procedures given are good for rescue of really screwed up parts or maybe blower motors; I've just recently salvaged a horribly machined Spitfire block with appropriate copper wires in strategic locations. I've never planed a head or block just for flatness in a simple bad gasket situation - only when the gasket face was obviously damaged or when I was doing other stuff that required true surfaces or for compression increases. Everything clean and dry, head and block reasonably flat, put it together and follow my correct retorque program, as handed down to me by real Mechanics from the days when men built and fixed machines based on reality and knowledge, not rumor and laziness. My typical head installation procedure is as follows; the example is for an MGB. The factory manual calls for 45-50 lbft, studs appear to be variably black oxide or phosphated, nothing is specified as to lubricant. Head and block are cast iron. Using anti-seize in accord with my argument above, I use the 45lbft figure, which is minus 10% from the maximum. Clean head and block with Brakekleen or lacquer thinner to remove all oil, install gasket with factory sealant coating only, and install head. Put good (smooth & flat) heavy hardened washers on studs, coat threads and washer faces with anti-seize. Install nuts; tighten to 10lbft, then 20 in sequence. If time allows, do something else for a while, several hours if possible; repeat tightening to 30, then 40. If possible, I like to leave it overnight, or at least while I assemble everything else. The time between cycles allows the gasket to settle, resulting in greater stability at the higher torques. The next day I will check torque at 40 and adjust the valves to slightly greater than usual clearances, .018-20 as opposed to .015, and start the engine. ( I don't even use a gauge for this preliminary valve adjustment, just close the screw down to zero and back off 2 flats and lock the nut. For those who believe that retorque is not necessary, gasket settling can easily close the valves to near zero clearance; it's really annoying to burn valves when you did all this work for a valve job!) Get to running temperature while checking for leaks and rough adjusting carbs. Once at running temp for 10 minutes, shut down, final torque while warm to 45lbft, adjust valves to normal. (I know it says to adjust valves cold. The guy I first worked for was a BMC service manager; he pointed out to the BMC factory chief service rep that they had specified variously hot, cold, and cold running (!), all at the same measurement. They measured, and I have measured - it matters not on this engine.) If it is convenient, or if it involved a full rebuild, I like to keep the car for a day or two, and put the first 50 miles at least on it; I will also cycle it between running temp and cold a couple of times. A final recheck of torque and valves will normally show absolute stability at this time. I specify that it come back for retorque after roughly 500 miles or a month. I have found that the time delays in the intermediate stages of tightening result in much less movement at both the first hot and 500 mile retorques. Some dealers in the Pittsburgh area in the late 1960s did not do the pre-delivery and 500 mile retorques, despite being paid to do so by the factory. These cars blew head gaskets routinely at 3-6000miles. I further recommend retorque at subsequent approximate two-year intervals. Movements are small on these, and I never experience the typical MGB seepage, which usually shows in the 30-50,000 mile range when the first hot & 500 mile checks were done, but not the later ones. On engines that have not had the post-500 mile retorques by this mileage, I find that some of the nuts are usually somewhere in the 25-35lbft range. As an example of later additional retorques, I have recently checked an MGB, which I did according to my above procedure. Since head install = 2250mi, 13mo; Since last (500 mile) retorque = 1750mi, 11mo. All nuts moved approximately 15º, except the RH rear and rear center nuts moved 25º. This is typical behavior, on engines assembled as specified. Those which have not been assembled this way show much greater movement, and occasionally, blown gaskets. I have salvaged seeping gaskets through prompt retorque, but it won’t work after pieces start sticking out the side, or if the gasket has failed between cylinders! If an engine is overheated for any reason, then the head should be retorqued after the problem is remedied – this will frequently save later gasket failure. Any engine that has sat for long periods of time should be retorqued, especially if the head had been recently installed before the lay-up. I repeat that time and heat/cool cycles are the critical factors in gasket settling, not mileage. As of Fall 2009, I have just solved a nasty oil leak from the head gasket of one of my Mazdas by retorquing the head. Car shows 135,000 miles, has been leaking progressively more since I got it at 102.000 – doesn't leak anymore! Retorque or check requires that you back off the nut 1/4 turn and pull to spec in one smooth, continuous movement. Static friction will frequently cause torque readings as much as 50% high before break-away, even worse for galled/scored washers and nut faces. If the “feel” is erratic, it almost always indicates galling somewhere - investigate and fix. I have found that either fast or extremely slow movement of the torque wrench will cause wildly erratic results. In particular, extremely slow pulls with click type wrenches can make the wrench not “break” until torques are far in excess of the setting. This is largely due to friction in the wrench and could easily result in breakage of fasteners. A fast pull can cause a wrench set at 50lbft to “break” at 35; I have measured extremely slow “50 lbft” pulls at over 75lbft as determined by angular measurement, and the wrench never “broke”. Flexible beam wrenches are less prone to this problem, but still show the same tendency, due to the friction in the fastener rather than in the wrench. The replacement “heavy duty” thick washers now supplied for MG by major suppliers are trash – they are not hardened as the originals were, evidently the same cheese as the TR nuts. Good hardened washers can be gotten from machine shop supply places, “case hardened finished washers” commonly used in tooling. They should be 1/8 to 3/16” thick and case hardened. Cast iron heads are final torqued and retorqued while warm, aluminum heads are always done cold. By experience, it makes little difference what the temperature is for CI, but cold is critical for aluminum. The expansion coefficients for studs and CI are close, but Cx for aluminum is much greater than the stud, which means that the aluminum head will be tighter than spec when hot, or, if you torque to spec hot, then it will be loose when cold. What does it all add up to? I have never had a gasket failure on any engine (probably around a thousand) that I have done this way. I have successfully assembled engines that had block or head faces way out-of-spec, I have successfully reused head gaskets with tens of thousands of miles of previous “experience”; not recommended, but sometimes you need to put it together with no new bits on hand. I have never broken an OE stud, or stripped a nut that hadn’t been previously abused – Triumph head nuts are made of cheese, but they work if you are careful! I replace Triumph nuts with MGB ones, which are better and longer, giving more threads to take the load. Current replacement MG nuts are in fact “SAE high nuts”, longer still and you must be careful on Triumph or 1500 midget, since they may interfere with the end rocker stands, easily fixed by cutting little notches to clear the nuts. Torque To Yield Bolts, Savior or Scam? The following is my diatribe on yet another apparent scam by the corporate world, visited on gullible consumers, mechanics, even engineers. I had a Ford Taurus, which ate its head gaskets, not for the first time, though it is the first since the car has been in my possession. I found that Ford says you must replace the head bolts when they are removed, and wondered why. An Internet search turned up a lot of noise re: “Torque To Yield” bolts used in much new machinery. This sounded altogether too much like the old joke -- “How tight are these supposed to be?” “Tighten ‘em up till they feel soft and back ‘em off a quarter turn.” The best description I found came from UMR Engines in Australia. Quotes below are from that description, found here: http://www.engineproblem.com.au/main.htm > procedures > TTY head bolts In order to totally understand this you should read the full article. This is an excellent site, with a lot of clear tech info. (I was right on the joke, but they don’t even back it off the quarter turn.) “The difference with this plastic stage is that at this point the bolt may not return to the original length when removed. In the plastic stage not a lot of extra clamping tension is reached but the bolt will tend to hold the required clamping tension even as the gasket crushes in service. This feature has allowed manufacturers to suggest that a head re-tension is not necessary.” This is total nonsense. By definition, no bolt is ever working in the plastic range. Once the bolt reaches plastic yield it stretches, reducing the load to the elastic limit; the only possible gain is due to uncontrolled cold-work of the bolt increasing the elastic limit. If the gasket permanently compresses after the initial tightening, the load will drop further into the elastic range. If, through TTY or by good luck, the bolt is at its elastic limit, any further thermal expansion of the clamped assembly will permanently stretch the bolt, by definition. The sole exception would be if the thermal expansion characteristics of bolt and clamped parts were identical. Otherwise, when it cools, the bolt will be loose. If you are lucky, it will now be back in the elastic range (instead of broken), with sufficient clamping force to stay together. The second possibility is that the clamp loads of the high strength bolt exceed the compressive/shear yield of the clamped (frequently soft alloy) parts; the entire thickness acts like the gasket, dropping loads still further into the elastic, unless it breaks or bends the casting. I have not been impressed with the load distributing/washer design of the late model engines I’ve seen. In fact, it appears to me that all the TTY scheme accomplishes is limiting the maximum load to the elastic limit of the bolt. This may be of benefit in limiting crushing and shearing of the clamped parts, but it certainly does not improve clamp load retention in any other way. You don’t need fancy bolts, just good washers; large diameter with relieved faces around the bolt shank. The clamp load will always be equal to or less than the elastic limit of the bolt. The correct application would be to tighten to some figure that gives maximum load in the elastic range under any feasible condition, like high operating temperatures, as limited by properties of clamped parts. 75% of elastic yield is a commonly used figure, giving safe “slack” in the real world. High load, high performance bits that can be expected to be assembled more carefully may go up to 90 or 95%. Again from the UMR site: “Slowly all future production engines will change from using head bolts that are tensioned to a predetermined torque setting to the use of "torque to yield" head bolts. The reasons behind the change are: Engine design has reduced the number of head bolts. Engine design has increased the length of head bolts. (FRM: This second point is an advantage: the bolts, acting as springs, vary in exactly the same way for different lengths -- one inch of bolt corresponds to one inch of casting, etc -- within the elastic; the thicker castings distribute the load more evenly, as long as the immediate underhead area is not locally stressed beyond compressive/shear yield) Higher performance outputs require higher clamping loads. Lighter castings require more consistent clamping loads.” Less bolts and lighter castings guarantee LESS consistent clamping loads. Tightening the bolts more in order to retain similar total clamp loads increases the stress gradients from “under bolt” to “away from bolt” areas in shear, compression, and bending. I have no doubt that this is a reason for the increasing incidence of blown gaskets and cracked castings. I believe that this entire theory is misguided at best. At worst, it is a scam to cover poor design and bad service procedures. The only possible advantage is in saving a very small amount in bolt, hole, and assembly costs. The savings in number and material of bolts is for OEM manufacturers only; as a service problem it leads only to expensive parts, if you can get them at all. It provides an “out” for wretched designs, which necessitate dismantling half the engine to tighten the head bolts, transforming a 15-30 minute, once every few years service procedure into a major engine failure at slightly longer intervals. Under the guise of “reduce weight, increase efficiency” we are afflicted with unreliable vehicles that range from impossible to expensive to repair. Marketing replaces the minimal weight savings with a few hundred pounds of cup holders, plastic trim, and electronic garbage. I have little doubt that manufacturers are losing more in recalls and repairs, plus customer dissatisfaction, than they save in bolts. There were many millions of cars that had no head gasket problems, given an occasional retorque. When they did fail, they could be fixed with nothing more than new gaskets and careful assembly and service. I have been fixing cars, much of the time as a business, for 40 years; I have never had a gasket failure on an engine I assembled and serviced. I retorque regular customer’s heads every year or two as routine. This represents mostly British cars, but ranges from flathead Fords through various motorcycles to Cummins diesels. The Taurus has gone through two sets of gaskets and bolts, and is blown again, at 162,000 miles; and, this is the “good” 3.0 L Taurus, not the 3.8 L one that eats gaskets a lot! This subject is a prime example of why I’ve been saying for years that nobody should be allowed to design any machine until they have worked as a mechanic for several years. This kind of thing was also a major factor in my dropping out of engineering school -- “they” wouldn’t listen to a mechanic’s observations, even though they couldn’t out-argue those points. They try to tell us that many of the gasket problems are the result of differential expansion of light alloy heads with iron blocks, which does not explain the 3.0L Taurus, which is iron/iron. There are millions of vehicles with alloy/iron engines that have no such trouble. Various Toyotas are a case in point. I have had many people tell me that they have these with 250,000+ miles, never had a wrench on them. While these are evidence that it is possible to build an engine that does not need retorque, it does not mean that it is in fact being done universally. I have cared for many XK Jaguars, Rover 2000, Sunbeams - all alloy heads, no blown gaskets. Of course, I did retorque these regularly. To be sure, there were the Saab 99/TR7 and the 2x version called a Triumph Stag, which could be awful in this regard, but that may have been due to overheating from other causes. More frightening is the apparent increasing use of this foolishness in suspension systems - my Taurus book says that any suspension bolts removed must be replaced on reassembly. Imagine the loads when you hit a pothole with TTY bolts in your suspension, already stressed to their limits. The bolts are all going to be loose afterwards, leading to fatigue failures or fall-out at inopportune moments. You would likely be better off if they broke on impact. This may represent an attempt to deal with loss of self-locking properties of the fasteners. In that case, please tell us so; I have whole bottles of locking materials, as well as cotter pins, lockwire, and locktabs available. In general, it is unrealistic to expect the service technician to tie up the job to wait for apparently unnecessary parts from poorly stocked or distant OEM suppliers. We are, however, not interested in losing customers due to fastener failure. It is certainly best to use the “snug + angle” system, which requires tightening by torque to a defined “snug” condition, then final tightening a specified number of degrees of fastener turning. I’ve been doing it for years, partly because I couldn’t afford the giant torque wrench to service my Cummins diesel. I have known for years that torque to spec is dicey; after you tighten a few hundred bolts to some spec it is very obvious that there is a lot of variance; it is equally easy to observe and record the correct angle movement to get it consistent. Two stroke Saabs formerly came with a neat little protractor in the toolkit, so that owners could decarbonize and replace the head correctly. As I recall, it cost a whole dollar. It must be realized that the angle for any given degree of stretch or clamping is dependent on all of the parameters of the fastener and the clamped parts. For the torque method, the torque would directly translate into a specific clamping force for any given fastener, but for the addition of substantial and largely uncontrolled errors from friction at both the thread and the bearing surface. Put another way, for torque spec applications anything which affects the friction must be specified and controlled; for angle specs the geometry and material characteristics govern, and each case will have its specific angle. See my addendum at the end of this piece re: friction and lubrication on threaded fasteners. TTY is only suitable for fundamentally one-use items which do not experience extensive and repeated load cycling, thermal or otherwise -- top level race engines and one-use rocket boosters, which require absolute minimum weight. If any reader can coherently point out the error of my thought, I’d be glad to listen. Please reply to mailto:gofanu@cust.usachoice.net Excellent basic info on fasteners: http://www.arp-bolts.com/pages/tech/fastener.html Wheels Road wheels present severe problems. They are subject to extreme and unpredictable loads, subject to amazing abuse, and are all-important to life and limb. Most if not all “authorities”, like wheel and rim manufacturers’ organizations, say to never apply lubricants. I have concluded that their recommendations are based on preventing overtorque and consequent breakage. Users will advise the same, apparently as a result of stories or experience with wheels coming loose. The belief seems to be that if the nut is easy to turn, it will unscrew itself. The truth is that if properly tightened, they will NOT unscrew themselves, and this can be ensured by checking torque after some mileage, which is almost universally recommended and very rarely done. Wheel nuts that fall off were not tightened correctly in the first place. Breakage may be caused by overtorque in tightening, overtorque due to galling (sometimes the nut is not even in contact with the wheel), or fatigue. The preceding arguments regarding repeatability of torque readings and fatigue apply. In fact, virtually all wheel studs/bolts have surface coatings. Shiny black is oxide, dull black is usually phosphate, white-silver is cadmium, blue-silver is usually zinc. Chromates are silverish normally and may be dyed with some tint. While the manufacturers’ specs may apply to clean and nearly new fasteners, they clearly are deficient in real-world situations. Repeated removal/installation cycles wear out the coatings under the best of circumstances, corrosion from moisture and salt in dry threads cause surface changes and physical interference since the corrosion products are usually larger in volume than the metal they derive from. Road dirt on threads acts as a wedge and an abrasive, destroying both artificial coatings and natural oxides. Galling ensues on subsequent cycles, aggravating the problem. All of these conditions as well as initial uncertainties can be ameliorated by the use of anti-seize compounds. The worst single offender is the use of high speed impact wrenches, especially in combination with these other factors. While they can be set to an approximate torque, it is imprecise and subject to operator finesse. In any event, they are rarely turned down from “Max”, and are frequently operated on excessive air pressures despite the ratings at 90 psi maximum. A 1/2 drive wrench is commonly rated at 200 lbft at 90 psi., and it will go much higher if you let it hammer away. In a better than average tire shop, I have observed a technician remove and install wheels on a 3/4 ton pickup truck, which takes something like 100 lbft as a bare minimum; then he used the same tool, with no resetting, to put alloy wheels on a late model VW. For the finishing touch, he “checked” the nuts (on the VW only) with a torque wrench! On removal, impact wrenches will drive a nut over large quantities of dirt and rust, with serious galling either then or on reinstallation, since the dirt grinds off any lubrication present. The gross energy input and high speed of this process can easily make the nut too hot to hold. Since the heat is generated primarily at the thread contact surface, it is likely that local temperatures were at several hundred degrees minimum. This is likely above normal tempering temperatures, which means that at least the threads are now in an annealed condition. I observed a lot of galling and broken studs when I operated a heavy duty truck; the truck shops use 3/4 or 1 inch wrenches capable of upwards of 600 lbft. The worst case was when I had flat tires on a company trailer. The nuts showed signs of fretting corrosion, which means that they were effectively loose - see notes below. Nevertheless, when the tire shop tried to remove them, they would simply not move, even with the 1 inch impact. A breaker bar about 8 ft long succeeded in turning them, but the galling was so severe that the nuts simply turned on the studs, without unscrewing. Some of the nuts were no longer in contact with the wheel when this happened. Examination after cutting them off showed that the entire thread area inside the nut had welded to the nut and torn away from the stud. This cost me a day’s work, and several hundred dollars to the company for stud replacement. I once had a new customer bring in a fairly new Volvo, c. 1970. The nut/stud materials used on these cars were especially prone to galling. As we reconstructed events, this car had had snow tires fitted and switched back to summers twice at a large tire shop (no question on the high speed air wrench), so the wheels had been removed and replaced maybe 6 times max. We attempted to remove the wheels for routine state inspection, and encountered the same condition as in the preceding paragraph. None of the 20 nuts would move! We tried heat, and very long bars. Finally we had to cut them all off. No dealer had more than a few stud/nut assemblies available, I sent guys out to every dealer within a 50 mile radius and still had to order some. Many manufacturers say that if you have to replace 2 studs on a hub, you should replace the hub complete. While we did not do this, the cost to the customer was about $300 at a time when a new Volvo cost about $3000, or 10% of the new car cost. I barely covered my costs (if I did), and the customer lost the car for 2 weeks. Some cars, like Triumph Spitfires with chrome cap nuts, have “rubber” nuts - they are very soft. These take 38-42 lbft. When the impact wrench hits it at 200+ ftlb, the usual result is that the nut strips. The studs are very high quality, black phosphate finshed, and are rarely damaged. If the studs are damaged they will take out a new nut first time on, but it will not be apparent until the first time off, unless you are heavy-handed in tightening. I replace a lot of Spitfire nuts at about $5 each. I have a Mercedes-Benz manual for a 380SEL, which says: “Experience has shown that impact wrenches will already obtain a torque of 60-70 nm (app.45-50lbft) under a single impact”, “There should be no dirt or grease on the spherical collar of the (wheel) bolts”, “Replace screws with damaged threads, worn zinc layer on spherical collar, and with corroded spherical collar”, “Retighten after 100-500km” I find nothing about lubrication on the threads themselves, but note the importance of the zinc layer, which acts as an anti-seize compound. I have seen many cases of galling on the contact faces of wheel fixings; short of replacing parts, I believe that A-S is the remedy. My wheel procedure goes like this. Removal: Clean exposed threads, lubricate with light oil or penetrant. Break loose with breaker bar, noting any roughness or squeaking. Either indicates no lubrication, and may be a sign of galling. Spin off with ratchet or air wrench set low. Clean and inspect all parts. Replacement: Lube with A-S. Tighten with ratchet, in stages and cross-sequence until snug. Tighten with torque wrench in stages like on a head (no reason to wait between stages) to either low limit or 15% under spec if no range is given. Retorque after 25-50 miles. Check again at 500 miles or so. Following this procedure, I find no movement at 500, except on big truck wheels sometimes, or wheels that are either new or damaged in some way, usually galled nut seat faces. Be aware that some wheels, like the M-B cited, have spherical rather than conical seats, and some alloy wheels use shouldered flat-face nuts. Be careful when switching wheels or nuts about. You are probably OK in omitting this step otherwise. I have never broken a stud or bolt on tightening. They break on the road, if damaged or from fatigue. I consider studs broken on the road as a good indication that at least all the ones on that wheel should be replaced soon. They break on removal, if corroded, or galled by dry installation with an air wrench. I have never had a nut come loose. Anti-seize and a torque wrench, together with careful use of your brain, will prevent all such problems if the studs/bolts are good. All that said, be aware that this procedure is contradictory to most recommendations; it is up to you to be responsible for your use of this information. Notes on wheel nuts “Went for a drive up a very rough road yesterday and one of the rear wheels FELL OFF. Most disconcerting. The nuts had worked there way almost all the way through the wheels and then loosened themselves off. Road was so rough I never heard the wheel coming loose. “ Tony Oliver Such failure is almost-to-absolutely invariably the result of the nuts being loose in the first place. Wrong nuts usually damage the wheel as they reshape it, but if it tightens to final torque it will not loosen. Switching different shaped nuts around on a wheel will eventually wear it out, but will rarely come loose if tightened correctly. Wheels might crack from age fatigue, but even those failures are generally begun by loose bolts. Nuts with rusty or dry threads will loosen because they are not correctly tightened. By now you no doubt realize that this failure is of the (possibly past) pit crew, not the parts! The nuts must fit the stud threads and the wheel seat they tighten to. Nut seats are various angles: 45 deg was common, 60 seems to be more common now -and there may be others. Mercedes and other Euro use true spherical seats. And of course a zillion variants of straight-shank shouldered nuts on alloy wheels. Some alloys use tapers, with or without cast or pressed-in steel inserts in the wheel. I think the OE Magnette nuts are semi-ball faced (my cars are buried in the snow just now!), which is a taper with radiused surfaces - many cars now have plain tapers. As I said, tapers may differ; so examine the wheels carefully. June 09 update: I have recently bought a really nice set of Italian alloy aftermarket wheels, which came off a 1986 Acura. They have ball nut seats, evidently standards on some Honda/Acura; I do not know if these nuts are standard Japanese or standard Italian, or if they are to the same European standard as MB/BMW/Porsche, or even if there is a European standard. I've seen BMW wheels with ball faced, but I have some stock BMW alloys with 60 degree ones, no inserts. Most Japanese alloys use 60 degree tapers, as near as I can tell, certainly Mazda do, with pressed in steel inserts. I do know that some idjut used 60 degree taper nuts on some studs (and not always the same ones) though!. (I got 12 nuts of 16, with 8 ball face and 4 60 degree.)So, I must figure out how to reseat the nuts to one system or the other. The nut must tighten down on the wheel before it bottoms on the hub or thread end - this can be a problem on worn wheels or wheels designed for larger studs, or with closed-end nuts. Use of taper nuts on ball-faced wheels can do the same. Over tightened wheels will eventually suffer from this, as the nut works it's way through the wheel - failure by loose! This can be checked by screwing the nut all the way on the stud without wheel, and measuring the projection of the stud through the nut; then install the wheel, tighten to torque spec, and repeat the measurement. The nut should be at least one full thread out from where it was sans wheel. Sometimes taking a bit off the small end of the taper can fix this, but watch for bottoming on the thread end or shoulders. Miscellaneous notes It should be apparent from all the uncertainty involved in this subject that it is very difficult to be precise in these matters unless you have a lab and a lot of time to investigate your particular problem. The fact that so many things work as well as they do tells us that there is a bit of latitude, usually a fairly large bit. Those machines that are “on the edge” may have recurring trouble; this usually becomes known after a while, and people figure out cures. For the rest, find out from somebody with a lot of experience what works and follow instructions carefully. The guy who did a few engines, or heard from a friend about a guy who claimed to have done something, is not an authority; these tales may however indicate a route for investigation. I suspect that it would be theoretically correct in many cases to drop torque specs a bit more than I usually do when using A-S, based on some references such as ARP. The BMW references above seem to indicate that phosphate or galvanizing (zinc plate) are equivalent and oil does not matter with them, but wax does, probably due to greater friction reduction under high pressure than oil. Cadmium plate calls for a 30% reduction; this may be the high possible limit for torque reduction. It is possible that lead, tin and silver would be similar, and modern high tech lubes may approach this figure. If the oil in these cases does not matter to torque (it does to corrosion), and the metallic components in A-S duplicate the coating characteristics to some extent, then we are left with the graphite contribution. Graphite is a very good EP lube, but probably not better than the cad plate. Depending on the graphite factor, it would appear that A-S would call for a reduction in torque of greater than 0 and less than 30%. On cad plated fasteners, I doubt if any reduction for A-S is needed. I have had no failures, either stripping/breakage or loosening, at my usual numbers; but, for assemblies involving aluminum parts, tend to drop the numbers by 15 or 20% rather than 10. I then carefully observe what happens over time. Your torque wrench is NOT a breaker bar or ratchet for daily use! “Click” wrenches in particular should never be pulled above the set click point. Use a breaker bar or ratchet to back off nuts on retorque or disassembly. Torque wrenches should be recalibrated periodically, but good ones hold calibration well if not abused, especially if they are kept dry and used not too often. Deflecting beam type torque wrenches are inherently accurate – the torque deflection is a characteristic of the beam material, and does not change. They have two main error sources, assuming the needle reads zero at rest: There is a pivot pin in the handle, and the wrench must be used so that the handle is not touching the beam at any place other than the pin. Allowing this means that the calibration center difference is either too long or too short. Secondly, if the wrench is pulled so that the indicator needle drags on the dial slot, the wrench will read low. Pull must be in a plane perpendicular to the bolt axis. Factory shop manuals are excellent sources for general education on automotive practice. They vary by country and make; German ones are great for precise engineering considerations, Triumph tends to give torque specs for practically every bolt, nut, and screw in the cars. You must study them for the accompanying conditions in order to understand the torque specs and applications. It will be seen that older books give torque specs only for critical or unusual fasteners; “standard:”, i.e. not “long series”, wrenches are made to allow a normal man to correctly tighten a normal bolt with reasonable effort. The current fashion for long lists of torque specs is a consequence of the loss of skill and knowledge, fed by lawyers and fears of liability. Red oxide stains emanating from tight fixings are evidence of lack of lubrication and small constant movement; the end consequence is galling or fatigue failure cracks or both. This is called fretting corrosion. It is common in dry splined connections. For a real fright, go to a truck stop and look at a bunch of trucks with Budd wheels - the ones with 8 or 10 studs. The ones with red oxide stains (or black on alloy wheels) coming out from the studs are in line for wheel or stud failure from fatigue cracking! Most wheels using tapered or spherical nuts are “coined” around the boltholes. This provides a stress limiting/relief cushion, spreading loads at the fastener. The fastener distorts the wheel somewhat, making things less “touchy”. Cheap aftermarket wheels frequently are made of flat plate and have a tendency to work loose or crack due to local high stress under the fastener. The coining can be partly simulated by a machined recess on the back, directly under the bolt, though it does not provide the material improvement of coining. If you have flat back wheels, attend carefully to torque specs and inspect frequently. All the preceding is based on a lifetime of experience, careful study, and much thought and testing. It is advice, not definitive; a further bit of advice is to always attempt to find out the manufacturers’ statements, and know why you are deviating from it! Use at your own risk. Remember that all of the above are “rules of thumb”, and one does occasionally hit thumb with hammer! Be safe, have fun. British Threads & Tools Whitworth didn’t come up with these sizes arbitrarily, they were calculated to optimum for material strength and loading and efficiency, and his were the first standardization of bolt sizes. As materials changed, those optimums went off a bit. If other people had just used his standards instead of inventing their own, we’d be less confused today. We have only recently gotten to Whitworth’s niceties of rounded crests and roots, in the UNJ (mostly aerospace, high stress) standard. The wrenches say 1/4W and/or 5/16 BSF because originally this was the calculated size for a 1/4W bolt, before it was British Standard Whitworth. When it was decided to make fine threads- BSF(ine)-, the head size was reduced one increment, since these were used where space was a problem (and materials were better). Then they standardized the sizes to BSW & BSF, but the old name stuck, hence 5/16 bolts with 1/4 W wrench size. So, the proper nomenclature would be 1/4W for old wrenches, 1/4W-5/16BSF for the ones in the middle, and plain 5/16BS (covering both BSW & BSF) for ones after the standardization. I have tools marked all 3 ways. Same thing happened in the USA - USS or National Standard or NC(coarse) 1/4 bolts originally had 1/2” heads, then SAE (fine)came along - 1/4 bolt with 7/16 head, then all 1/4 bolts were standardized to the SAE size heads. The UN(ified) standard series arose when the Brits started using “American” bolts, and it was necessary to make English and American “American” bolts interchangeable - late 40’s to early 50’s. British wrenches for American bolts are usually marked with the actual wrench opening -7/16 A(merican)F(ine) or possibly Across Flats, but I once saw one that was 7/16, marked 1/4 AF! It seems that mechanics are somehow programmed to regard tools as sacred, but parts as replaceable. Unless they have experience as toolmakers, they won’t modify a tool! Those of us who work on the obsolete, unusual, and non-standard, soon learn that the parts are what are important; and (eventually), since we keep coming up with the same problem, that we need to make the tool suit. DON’T FILE NUTS/BOLTS DOWN!! It will, sooner or later, lead to a disastrous mixup, especially on cars that already have a hodge of thread & wrench sizes. Even if you get some real Brit tools, you won’t be happy about cutting them up to get in some nasty corner.at 2 AM on a holiday. So get some Sears or Taiwan or hardware store ones, and make ‘em work in less time than it takes to call a supplier. Here’s a nice table from comrades in wrenching: http://www.team.net/sol/tech/SpannerSize.html From this, for the most common cases: 2BA = .324” = 8MM + .009” 3/16W - 1/4BS = .445” = 7/16 + .007 = 11MM + .012 1/4W - 5/16BS = .525” = 13MM + .013 = 1/2 + .025 5/16W - 3/8BS = .600” = 15mm + .009 3/8W - 7/16BS = .710” = 18MM +.001 7/16W - 1/2BS = .820” = 13/16 + .007 1/2W - 9/16BS = .920” = 23MM + .014 = 7/8 + .045 (if you can’t find 23MM) Now, wrenches are made typically .004 - .012 oversize to cover tolerances in fastener and tool, tending greater as size increases. Therefore, you don’t have to take off the full amount, but give yourself some clearance. Many times a 7/16 will fit snugly on a 1/4 BS, 18MM should always work on 7/16 BS, 13/16 usually fits 1/2 BS. For the others, get a GOOD little file. The only trouble is the chromeplate, which usually isn’t very heavy on inside surfaces. Hold wrench in a vise, parallel to jaws, use heavy pressure with the coarsest file that fits on the first pass, or take off the cp with a mini/Dremel grinder. Remember that you are only taking off a few thou. On open ends, you only do one face. Measure with a dial caliper; you can make ‘em fit better than store bought. Widely available Chinese dial calipers are about $15 - I’ve compared mine with Starrett & Mitutoyo - exactly the same measurements. Box ends are a bit harder to keep track of, but less work,, especially 12 points. Most good quality recent (last 25 yrs) boxes are “Flank drive” (Snap-on ™, I think), which means that inside corners are relieved (no sharp internal corners) so that they don’t touch the fastener. The “flats” are also skewed, as if it’s already worn out. Some don’t have “flats”, but a rounded profile. Just bridge 2 adjacent “points” and file away. These require even less material removal, but if you have to take a lot out you may need to deepen the corner relief. [I just measured a brand new Craftsmen 15 MM 12 point flank drive box. It is .608 at the deepest part of “opposed flats”{at bolt corner}, and .599-.600 at the shallowest {near middle of bolt flat}. So to make it a usable 3/8 BS with .005 clearance, you need a file that will bridge 2 adjacent internal points, taking off only about .002 - .003 max off the very tips of each set.] This makes it easier to only file the faces, but harder to keep track. You have to mark faces to keep track, get it clean and use magic marker or better a light coat of flat black spray paint. Once you file, it’ll get shiny. Do half the faces (all on one side of the tool) to half the measurement difference, then do the other half to total. Once you get the first set filed and measured, you can readily see how much needs to come off- about 1 good pass per pair should do. That’s 12 file strokes all told. You can make a sharp corner box into a flank drive with a small round file - little chain saw files are great on larger sizes, very hard. Flank drive are easier to use on slightly boogered bolts, won’t booger good bolts, and they are stronger and less likely to slip. This procedure lets you have things like flare nut and crowfoot wrenches that are real BS! You can now afford (financially and mentally) to cut off to fit tight spots, bend ‘em, or whatever. It takes a lot less time to do than to read about! Do yourself a favor - Grind off the original size markings and remark. Paint ‘em orange! Please give credit if you use this somewhere. Informed comments are welcome and appreciated. Fletcher R Millmore mailto:gofanu@usachoice.net http://users.usachoice.net/~gofanu/ ©Apr 2004, Mar 2007, Apr 2007, Jun 09 |
| Flip Brühl |
| WOW! |
| Tore |
| Yeah well, I cleaned and lightly oiled original bolts with 20w50 last time and it worked for me. Previous 2 attempts failed with simply cleaned threads. Therefore from my experience, clean and oil. Always use the hardened washers as well of course. If its a 1500 ;-) |
| Dave Squire |
| I've not noticed any recent postings from FRM and wondered if he is still with us. I certainly hope so. He is one of the most informative and knowledgeable people ever to have posted on the BBS. Anyone got any news of him? |
| Bernie Higginson |
| I torque dry; Keith Calver agrees with me. |
| David Smith |
| Lots of opinions out there, as always! According to this source, 10w40 oil does not make much of a difference from dry, but anti-seize increases the clamping force dramatically. http://benmlee.com/4runner/threads/threads.htm I may just stick to my old habit of lubricating threads with 20w50 oil, and then use the torque in the workshop manual -or perhaps just a litte less, like Keith Calver says. |
| Tore |
| Wow indeed! The way I was taught was this: make sure all threads and fasteners are completely clean and free of burrs and that they will do up and undo easily up to finger-tight and back. Then make sure all internal threads are clean and, if in a drilling open at only one end, are free of oil and water or other fluids (to prevent hydraulic cracking). External threads should be thoroughly oiled (clean engine oil is fine) and wiped clean so that no excess oil is visible. I've done it that way for 45 years and I don't think I've had any more failures than anyone else. |
| Nick Nakorn |
| there is no harm in oiling threads before torquing up a fastener; the point is that the standard way for manufacturers and suppliers to specify a torque setting is with dry threeads, so if you oil them you should reduce the torque setting or you will slightly over-tighten them (probably still within tolerance though) |
| David Smith |
| Ah yes, but, irrespective of dry or lubed, do you --- 1) Install the cylinder head nuts, and torque to the data figure in the w/s manual. Then run engine until hot, and then allow it to cool down, before re-checking the torque *COLD*. Recheck *COLD* again after say 100 miles? Or 2). Install the cylinder head nuts, and torque to the data figure in the w/s manual. Then run the engine until HOT, switch off, and then whilst still HOT, retighten the nuts to data figure in the w/s manual. Recheck *HOT* after 100 miles? Or some variation of the above? |
| Lawrence Slater |
| To my eternal shame I've never retorqued my cylinder head nuts. I've also never suffered a head gasket failure but then again the engine's only had 130,000 miles on it. :-) by the way, this re-torqueing business - do you slacken the nuts first? and if so, do you loosen them all at once then retorque them or loosen and tighten them one at a time? |
| graeme jackson |
| I'm now thinking that the BMC workshop manuals tell you exactly how to do it. All it says essentially is, install the nuts, tighten to the figure quoted in the data, and forget about it. No need to recheck hot or cold, and no need to lubricate them either. |
| Lawrence Slater |
| Bernie, Yes, Fletcher is still around. He posts occasionally on the MG Experience, I think mostly on the Magnette section. I don't recall him posting here since around the time Prop finally got his engine running. Graeme, I am in the retorque cold camp, and I loosen them a bit first, and one at a time. I do cold because the spec is for assembling an engine, and I have to believe that there is an assumption that the engine would be cold when it is being assembled. I retorque because that was the way I was taught, and if it is not needed, then it's like chicken soup for a cold. It can't hurt. Charley |
| C R Huff |
| Charley. Thanks for the heads up on Fletcher. Glad to hear he's still going strong. Also, thanks for your thoughts on retorquing. |
| Bernie Higginson |
| The article Tore, Norway, linked to, referenced 'Bolt science' http://www.boltscience.com/pages/info.htm . So I rang them up and asked. The answers were -- unless the manufacturer states otherwise -- 1). Torque COLD, and only check/retorque when COLD. At all other temperatures a completely different and unknown set of parameters apply, regarding friction, stretch, compression etc. 2). Friction on dry threads is likely to vary widely, and cause torque measurement innacuracies. Clean and 'lightly oiled' threads, are far more likely to exhibit the same friction, and thus produce the same clamping load for the measured torque. So oil lightly and only do it cold. |
| Lawrence Slater |
| 'Friction on dry threads is likely to vary widely' - did they say why? |
| David Smith |
| Seems to me that we are getting pretty close to a conclusion here. That´s nice! |
| Tore |
| I think he said something like although the threads all look the same, in fact they vary slightly, and that causes different friction. A bit of lube evens out the friction. |
| Lawrence Slater |
| Now that makes good sense to me Lawrence. |
| Dave Squire |
| I wonder how much difference there really is between "lightly oiled" and a more liberal use of oil on the threads. I imagine that most of it will be pretty efficiently squeezed out from the threads under pressure anyway. |
| Tore |
This thread was discussed between 22/09/2015 and 25/09/2015
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