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MG MGA - Engine Rebuild Checklist
I'm looking to put together my 1622 motor after a hiatus of not running due to a broken head stud.
The first thing was that when I took the tappets out I lost the order of which tappet went with which cam lobe. I was always told that was a critical thing to do. How critical is it that each tappet go with each cam lobe?
Second thing, is that since the cylinder head and block are being cleaned again I
|Jamie, regarding engine paint; I would use Hirsch engine enamel MG paint (do a web search). Its about $40 for a quart + $5/6 for shipping, much better than the Moss paint in terms of color and durability. You can easily brush onto the cast iron bits, spray on the sheet metal bits. I just refinished an engine using the Hirsh paint, I think you'll like it. |
Do you have pre-assembly lube?
Do you have new locktabs for the rods and new lock tab washers for the cam/crank?
How old is the timing chain/tensioner?
Why not put a new head gasket on, keep the old one for a spare?
Good Luck, George.
|Jamie, I just used a regular "rattle can" acrylic on my engine and found Volkswagen "Gambia Red" to be a rather pleasing maroon colour for the engine, it was quite close to the original colour that I found on my block. There shouldn't be any need for special high temperature paints on a water cooled block, I've used all sorts of "ordinary" paints on bits of MG engines over the years and never had trouble with them curling up or falling off. See if you can find a close match to the original MG engine colour at your local auto shop, two cans should be more than enough.|
|Thanks so much! |
I would love to use the quart can of paint, but my air compressor won't be where the car is... :-/
I do have pre-assembly lube, didn't remember about the lock tabs, so I'll throw a lock tab set into the mix of bits to order.
Anyone have any experience with ARP High Strength Head Stud Kits? Looks like they are about 1.5 times the cost of a standard set. I've had significant issues snapping head studs (why the motor isn't running to begin with) and am curious if they are worth the money...
|Jamie, calibrate your torque wrench. Studs should not snap. In my limited experience (6-7 top overhauls and one rebuild) I have never changed studs. Most were done before I had a torque wrench, and never had any problems.|
In fact I never heard of this problem til I joined this MG group!
|Check Barney's site for the answer on studs - in short, he didn't see the need for high strength studs and gives lots of advice for how to properly torque them, etc.|
|Don't try to torque the studs into the block either. Finger tight is fine, then torque the nuts at the head making sure you are using the proper washers. If this engine has been torn down a few times though and the studs never replaced, I'd maybe do that this time. I have the click/breakaway style torque wrench that I think I got on sale from Sears for $100. One of my best shop purchases ever- if I had to use one of those stupid needle-pointer types I'd probably just opt to not do it at all.|
|Mark J Michalak|
|I have just painted my entire engine by brush using an MG Maroon engine enamel from Frost (US owned?): http://www.frost.co.uk/item_Detail.asp?productID=8967|
I was pleasantly surprised how well the brush marks flowed in. The rocker cover looks as if it has been sprayed. I bought a 500ml can and still have just under a 1/4 left. It cost £19.50 ($30) plus postage.
I would normally have sprayed it, but it is too cold in the garage at the moment and her in doors would not allow me to use the spray gun in the utility room!
|I have gone through more studs than I can count.|
I have a torque wrench that should be good and I had questions about it, until my dad talked with one of his fellow instructors at the local tech college.
I had always gone on the knowledge that if you were torqing a bolt at say 50 ft/lbs that you needed to start at a percentage of that, like 50%, then work your way up to like 75% of the torque, then finally 100% of the torque.
The instructor said that this is incorrect. He said that the torque is cumulative. So when I was doing the 50%, 75%, 100% I actually had torqued to 25 ft/lbs, then 62.5 ft/lbs, and finally 112.5 ft/lbs. Some of those studs held up and some didn't...which makes sense. My workshop was more of a shear mechanics course than it was an attempt to install a cylinder head correctly. One other thing is that the torque wrench should pop on or about 1/8 of a turn. I have seen when a wrench won't pop and allows you to keep turning... The 1/8 of a turn is a sanity check in my opinion.
Barney's site didn't shed any light on the torquing proceedure, but I'll definitely be paying attention to the threads in the block, oiling them up, putting the studs in finger tight only (should I bottom them out or back off a 1/4 of a turn once I hit bottom?), then hand tightening with a ratchet, then finishing up with the torque wrench set at 50 lb/ft.
That motor certainly does look good. I think for convenience we'll just be ponying up on the Moss hella-expensive spray paint...
Thanks so much for the replies!
|That's a nice looking lump Steve, give yourself a pat on the back!|
|Re: torquing, I'm not exactly clear what you're saying about an 1/8th of a turn. I usually get my bolts snugged up with a ratchet (following the correct sequence) to the point where the wrench will pop after about a 1/2 turn, you want to be able to keep a constant consistent pressure on the wrench as you turn it. If the wrench doesn't pop as you described above then it's set wrong or you're twising the stud. If you find yourself in a situation where you need to retorque the nut, back it off 1/4 turn first, then retorque in one constant motion. Also pay attention to your shop manual and follow the correct torquing sequence. As far as the studs I would just run them in with two fingers until they stop, you shouldn't need to back them off but if someone else knows better please chime in. |
I don't know which head gasket you are using, but I use the black Payen gasket. Some say it's not necessary to retorque the head after 500 miles when using this gasket, but I did it anyway. Better safe than sorry.
|Mark J Michalak|
here is the link to Barney's commentary on torquing studs.
JIM in NH
|Hi JD. It is important that the tappets go back in their original spots if you are using the original camshaft. Each tappet "wears" to it's particular camshaft lobe. Changing tappet locations can accelerate wear on both the tappets and camshaft lobes! If you install a new camshaft, DO NOT install used tappets, use new ones! Using old tappets with a new camshaft will prematurely wear the new camshaft lobes. Camshaft lobes and lifters, both new and old, should be coated with Moly based assembly lube, or Moly based grease, to prevent excessive wear on start up, during break in. The engine should NOT be allowed to idle slowly, but should be run at 1500 to 2000 RPM for the first few minutes after the initial start. The higher revs are necessary to "load" the cam, and facilitate proper run in of the valve train components. Hope this helps, Glenn|
|Jamie, your instructor makes no sense. According to him, if you torque a stud sequentially at 5,10,15,20 etc, you will reach 75 ft lbs at a setting of 25, and 105 at a setting of 30. This is plainly nonsense.|
Glenn - the reason for revving at 1500-2000 is to get splash lubrication of the lobes - they are not pressure fed.
|Unfortunately I accidentally turned the block upside down without taking the tappets out and they spilled out onto the garage floor without me being able to number their sequence. Looks like that's a $60 mistake that requires a second set of tappets within 600 miles... <sigh>|
Once I install this motor and things are working I'm not doing a retorquing of the head gasket...period. This "retorqing" turned into 'Hey, let's rebuild the motor again at 600 miles' when I snapped #11 on the final wrench pass...
Art, I'm not sure I follow your explanation of, "...5,10,15,20 etc, you will reach 75 ft lbs at a setting of 25, and 105 at a setting of 30." The math for 75 ft-lbs makes sense if you torqued the bolt three times at 25 ft-lbs, but 30 ft-lbs three times would be 90 ft-lbs based on what I was describing. How would you get the 105 off of 30? Maybe there is some confusion in my explanation of the concept?!
|One more question, would you replace the main bearings and thrust washers after 500 miles? I was able to keep those in the correct order but was curious if you'd replace them or not.|
To get correct information you have to first disclose all the facts to BBS members.
If the engine has only done 500 miles since you replaced the tappets, main bearings and crankshaft thrust washers, none of these items would require replacement, even the tappets which were mixed.
You say that the cylinder block is going to be cleaned again. Why? You only broke a head stud.
How was it cleaned the first time? Were all the plugs in the block removed and replaced? If so, your excessive oil pressure may be due to a plug being put in the hole where the oil from the pressure relief valve returns from the block to the sump.
Are you aware of the diagram on Barney's website which shows which hole must be left unplugged?
|M F Anderson|
|The block needs to be cleaned because the mating surfaces of the head and block have surface rust that needs to be cleaned. Doing that would require some cleaning alone, but in my amateur attempt to remove the broken stud there were some metal flakes that were generated that I want no chance of finding their way into the engine or parts once things are buttoned up.|
Everything was cleaned and there weren't any issues with the oil pressure relief valve that would cause me to think that it was a culprit in the high oil pressure.
I have read the article on the oil passages, but without seeing things for myself haven't been able to match the article to what I see on my block. None of the plugs were removed for cleaning, don't know if that's a positive or negative. We're going to put an emphasis on oil passage and water jacket cleaning on the cleaning this time around...
|Jamie re- the "cumulative torque" effect - I was just emulating your example where if you torque first to 25, then 37.5 and finally 50 (settings on the wrench), the stud somehow sees 102.5 I just wanted to show a more extreme example of this wrong headed logic, IMHO. It's what we called "reductio ad absurdum" in maths classes.|
If your instructor is right, then a small child could apply immense force to tighten up anything, using this approach!
|I agree with Art. The "instructor" comments on torquing studs make no sense at all. Torque the head studs in the proper sequence using 10 lb increments. When the torque wrench "clicks" you have reached that torque setting within about +/- 5%. A beam type torque wrench is only accurate to about +/- 15%. |
|George, Why do you say that a beam type wrench is only 15% accurate? Not what I have learned and certainly not from my understanding of the physics involved. Yes, if you do not read the needle from directly above, But nobody would read any type of meter or gauge from an angle. You'll get parallax errors. There are places where you can't get directly above the wrench and then the click-wrench really shines. But the torquing the head bolts of an MGA is not such a case.|
As far as that "Instructor" goes, he should be fired if he gave such false info. I really can't imagine this is the case. There must have been some miscommunication somewhere.
|While you have the engine out it is a good time to check the condition of your motor mounts and the grounding strap to make sure that they are in good order. On your 1622 block, does it have the later type seal on the timing cover? If not, a change over to the MGB cover that take the modern seal is worthwhile. Did you check the ring gear when you did the rebuild? How about the throwout disk and the clutch fork bolt and sleeve? Cheap parts to replace while the engine is out of the car.|
|hi. The garage floor mixed tappets can be re used, it the machined bottom faces are resurfaced. Most engine rebuild shops can resurface the tappet bottoms at very reasonable cost. Cheers, Glenn|
|Hi Chuck. The 5%/15% "rule of thumb" is something I picked up along the way over 40 years of wrenchin'! I have no basis for stating it as fact, and I have used both types with no problems although I prefer the pre-set click type. Torque wrenches can be calibrated, and it would be an interesting exercise to compare the two. Maybe I'll do that someday, if I can only retire : )|
|Art and George-|
I couldn't agree more. The issue I'm having is called doubt. If I had the time to do so, I'd be spending my time doing analysis on these studs being provided to show that they are not being made to spec. The reason I have even entertained the torque wrench torqing techniques is because something isn't right. When I have followed the procedures like everyone has mentioned (10 lb-ft increments up to the 50 lb-ft) and have snapped over a full set of the newly-supplied head studs while only acheiving half of the torque settings, I seriously doubt that my torque wrench is to blame so it's either the technique or materials involved.... Now I'm just trying to see what ideas/techniques are out there. I asked for a new torque wrench for Christmas and Dad was doing an investigation to determine if we even needed a new one.
The only thing that made me think the cumulative effect was entertainable was that you can actually measure torque on a bolt by how many turns are on the bolt. This is common in garage door springs where people will tell you there are like 36 full turns or 72 half turns to install garage door springs. In bolts it's just the pitch and length of the bolt that can determine how much torque is on the bolt for a given distance into the hole. In my experience with the torque wrench, the bolts will move even if you haven't changed the setting on the wrench. When you are turning the bolt there is more torque on the bolt. In an ideal world the wrench should click prior to the bolt starting to turn if the wrench had just clicked... (This could go on a while...)
Keith, thanks for the checklist. Of all the things you mentioned, the clutch fork bolt and sleeve are the only things older than 500 miles, and they should be replaced! Thanks for helping me out! Everything else was replaced with the original rebuild.
Sounds like I'll have the machinest take a look at the tappets and let me know what he thinks! After seeing a few responses, I think the current garage floor mix of tappets being reused after 500 miles wouldn't be too much unlike using a brand new set on the cam that is in there right now.
|JD, I agree that after 500 miles you can just re-use your cam followers (tappets) in any order. |
The way you were previously applying torque (50%, 75% then 100%) is absolutely OK. No way to accumulate torque. Most likely reason for breaking studs is poor quality parts! It should also be noted that the same torque on an oiled fastener with plain washer will exert a much higher tension than a dry fastener and lock washer or nyloc (prevailing torque) nut.
|To add fuel to the torque debate, the real metric we'd like to measure is stud stretch as a indication of preload applied. Such devices are available, but are not economical for the DIY car guy, or most professional shops for that matter (we have one here at work, $$$$). Torque measurement is the best we can do, and quite adequate for most if not all automotive applications. I wonder what they do when building up Formula 1 or NASCAR engines....|
|There is a lot to be said about stud failure! They can fail in tension (= too much stretching) or they can fail in shear (= too much twisting) or the threads can give out, male or female. It would be nice to know which mode you were experiencing. In theory, a well oiled thread should impart very little torque to the stud per se. The torque reaction is shared by the stud and by the face of the nut on the surface being tightened. In a frictionless world, all of the torque would be converted to stretching the stud. In fact, even with friction coefficients of ~ 0.1, most of it is wasted. If a nut has seized or rusted on the threads, all of the torque is devoted to shearing the stud - most common failure undoing rusted fasteners.|
But do test your wrench, even if new. It is quite easy with a vice, bucket of water, a bathroom scale and some wire to hold the pail on the handle.
The garage spring analogy doesn't apply. The torque there comes from a pre-engineered spring calculation.
When you are tightening, look out for a "soft" feel, a sign that it is going to snap. If you can stop there, you can extract the stud and put a new one in without all that dismantling.
The studs were failing completely in shear...classic 45º angles right in the middle of the stud at the top part of the bottom (course) threads (as the threads started).
The "1/8 of a turn" example was my looking for a "soft" feel as the stud was approaching failure. I noticed when I would snap studs was when I would say put a 45 ft-lb torque on the stud and the wrench would pop but then I would go to 50 ft-lb and it would turn and turn and turn without popping. That was me trusting the wrench too much...!
|Jamie, Art is correct that you cannot add small amounts of torque to the head studs and expect them to add to a higher total torque figure.|
Once you have "nipped up" the studs ( nipped up as in just beyond finger tight),you can then torque the studs up to progressively higher torque settings. Make certain you use in the correct tightening sequence.
The IMPORTANT thing is that on the FINAL tightening of each stud your torque wrench MUST be set to the actual cylinder head torque setting recommended in the workshop manual.
As soon as the torque wrench clicks, stop pulling on it as it is quite easy to carry on turning the stud after the wrench clicks and if this happens you dont really know what torque you have applied.
I dont know what amount of torque is needed to shear a head stud but it must be WAY MORE than the recommended head tightening figure!
I would have your torque wrench checked very carefully if I were you.
One last thing, I bought a new torque wrench here in the UK last year as my old one had lost all the numbers from the dial after being immersed during some flooding.
I found that the new wrench was only calibrated in kg/meters and so when I re-tightened my cylinder head studs I had to convert the lb/ft figures to metric.
It may be worth checking that your torque wrench isnt metric as this would easilly explain the sheared studs.
Best of luck
This thread was discussed between 15/12/2009 and 19/12/2009
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