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MG MGB Technical Blown Head Gasket ?(2) BBS discussion at MG-Cars.net
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MG MGB Technical - Blown Head Gasket ?(2)
| Hello all, I was going to continue my old thread but I realized i needed fresh thinking on this issue. After discovering the head gasket in perfect shape i did as others suggested and starting searching for the culprit. I put everything back together and fired her up. After running for approx.. 20 minutes and doing the neighbor twice I brought it back in to the garage and looked for a leak. NONE. before I shut off the light I noticed bubbles from the exposed head nuts on the right front of the engine. Looking closer I discovered steam and fluid escaping from the front most side head nut and stud. Does that in fact mean a broken or cracked head? or is the gasket faulty and I just don't see it? Any suggestions will be appreciated!! |
| Peter Murray |
| Hi Peter Not coming from thermostat housing is it? We have seen a couple of heads cracked from thermostat to the front stud on plug side. I would try a sealant. Peter |
| peter burgess |
| Peter- Cracks are most commonly found in the side of the head between the #3 & #4 combustion chambers. You need to eliminate the variables in order to find out what is wrong. First, remove the head and have a machine shop check it for warpage. Second, check the head studs to see if they're stretched. Stretched cylinder head studs will not hold their torque settings and will lead to a leaking or blown cylinder head gasket and possibly a warped and/or cracked cylinder head. Repeated retorquing of stretched cylinder head studs will likely result in a cracked cylinder head. Do not attempt to replace them with bolts. When a bolt to is torqued, it is reacting to two different forces simultaneously, stretching and twisting. This being the case, a torque reading does not accurately reflect the amount of stretch of the fastener. On the other hand, when torque is applied to the nut, a properly installed stud will stretch only along its vertical axis. I never reuse the Original Equipment cylinder head studs because after 28 to 44 years of service, I cannot see the point in putting my trust in them. The financial cost of the implied mechanical complications of a blown cylinder head gasket just isn't worth the savings on the price of a set of new cylinder head studs. Vendors that sell what they claim is the equivalent of Original Equipment cylinder head studs never seem to be able to give any specifications on what they are selling, probably because they simply do not know and can't be bothered to find out if what they are selling is really equivalent to the Original Equipment item. That is why I use (and recommend) the ARP items, not because of their tensile strength. Do not make the common Beginner’s Mistake of presuming that because you have installed extra-strong cylinder head studs you can apply huge amounts of torque to their compression nuts in order to attain a more effective seal on the cylinder head gasket. This will most likely result in distortion of their mounting threads in the deck of the block. As a result, the clamping force will be reduced and the cylinder head studs will consequently loosen, leading in turn to a blown cylinder head gasket. In addition, over-torquing can crush the cylinder head gasket, also leading in turn to leakage of combustion gases and coolant, as well as a blown cylinder head gasket. Always use the torque values recommended by the manufacturer. Steel studs have a different coefficient of expansion than that of a cast iron block and preloading them will aggravate the effect of this factor by increasing stress on the block. If they are bottomed out against their shanks in the block, the consequent preloading can cause the deck area around them to distort upwards as they expand more than the block, and that could lead to a blown gasket, or even a cracked deck of the block. When the block cools, being a casting, it will tend to return to its original flat shape if it has not cracked. This, in turn, will drive you to despair when you try to figure out why your cylinder head gasket has been leaking. This becomes increasingly likely if material is removed from the deck of the block in order to significantly raise the compression ratio. Chamfer and retap the threads in the block prior to installing the cylinder head studs. Should the cylinder head stud spin or wobble in its threads when installed dry, check to be sure that the studs are not undersize. Do not make the all-too-common mistake of attempting to torque the cylinder head studs down as this may lead to cracking of the mounting lugs inside of the block. Because the cylinder head studs extend into lugs that serve the secondary purpose of reinforcing the deck of the block inside the coolant jacket, any cracking of the lugs will allow coolant to leak past the cylinder head studs and undermine the sealing of the gasket. It is always possible that a previous owner may have already made this mistake, so coat the bottom threads of the cylinder head stud with a flexible sealer such as Fel-Pro Gray Bolt Prep immediately prior to the torquing of the cylinder head. Torquing of the cylinder head stud nuts to their specified 45-50 Ft-lbs will accomplish the task of securing the studs in the block just fine. Never use a thread locking compound as it will result in damage to the threads whenever the studs are removed, thus rendering them useless. Coat the smooth shank of the cylinder head studs with copper grease or any other heat-resistant grease in order to prevent corrosion. This will make removal of the head in the future an easier task. Be aware that it is not unknown for suppliers to accidentally ship the wrong cylinder head studs. The eleven cylinder head studs of B Series engines are 3/8” (.375”) in diameter with the upper sections of having 24 threads per inch and the lower sections having 16 threads per inch. Seven of these are 4 ½” (4.5”) in length, while the remaining four are 6 ¼” (6.25”) in length. Use either the Original Equipment hardened thick cylinder head stud washers (BMC Part # PWN 106) or replacement items of the best quality (thick and with machined faces) (APT Part # W3834) on the cylinder head studs, never thin mild steel ones from a hardware store. Make sure that the washer seating surfaces are machined flat with an end mill after the cylinder head has been skimmed so that they will be on a parallel plane to the mating surface so that the torque readings will accurately reflect evenly distributed pressure. Put an anti-seize compound on the threads prior to installing the cylinder head compression nuts and torquing them to the cylinder head. While oiling of the threads is commonly done to protect from rust, the antisieze compound will do an adequate job of protecting the threads from corrosion. If you are really paranoid about the exposed sections of the threads corroding, then use 3/8”-24 UNF acorn nuts! When a cylinder head gasket is installed between the cylinder head and engine block, tightening the cylinder head stud compression nuts compresses the gasket slightly, forcing the soft facing material on the gasket to conform to the small irregularities on the mating surfaces of the cylinder head and deck of the block. This allows the gasket to “cold seal” so that it will not leak coolant before the engine is started. The cylinder head gasket’s ability to achieve a positive cold seal, as well as to maintain a long-lasting leak-free seal, depends on two things: its own ability to retain torque over time (which depends on the design of the gasket and the materials used in its construction), and the clamping force applied by the cylinder head stud compression nuts. Even the best cylinder head gasket will not maintain a tight seal if the cylinder head stud compression nuts have not been properly torqued down in the appropriate sequence. The amount of torque that is applied to the cylinder head stud compression nuts, as well as the order in which the bolts are tightened, combine to determine how the clamping force is distributed across the surface of the gasket. If one area of the gasket is under high clamping force while another area is not, it may allow the gasket to leak at the weakly clamped point, so the cylinder head stud compression nuts must be tightened to a specified value in a specified sequence in order to assure the best possible seal. Another consequence of failing to torque the cylinder head stud compression nuts properly can be cylinder head warpage. The uneven loading created by unevenly tightened cylinder head stud compression nuts can distort the cylinder head. Over a period of time, this may cause the cylinder head to take a permanent set. Use an accurate torque wrench to tighten standard type cylinder head stud compression nuts in 3 to 5 incremental steps following the recommended sequence and torque specifications. Tightening the cylinder head stud compression nuts down gradually creates an even clamping force on the gasket and minimizes distortion of both the cylinder head and the cylinder head gasket. It is a good idea to double-check the final torque readings on each cylinder head stud compression nut in order to make sure none have been missed and that the cylinder head stud nuts are retaining torque normally. If a cylinder head stud compression nut is not coming up to normal torque or is not holding a reading, it means trouble. Either the stud is stretching or the threads are pulling out of the block. If a gasket requires retorquing, run the engine until it reaches normal operating temperature, then shut it off and retighten each cylinder head stud compression nut in the same proper sequence as before while the engine is still warm. Should the engine have an aluminum alloy cylinder head, however, do not retorque the cylinder head stud compression nuts until the engine has cooled back down to room temperature. In the case of either type of cylinder head, when being removed their cylinder head stud compression nuts should be systematically loosened using the same pattern and manner as that used when they are torqued down. |
| Steve S. |
| Thank you all and an special thank you to Steve, thats a lot of info to digest. I believe one statement you made about a previous owner over torquing is the most probable and I am now experiencing the consequences. |
| Peter Murray |
| Peter- Ah, DPOs! Yes, it does seem like a lot to digest, but its all worth knowing. |
| Steve S. |
| Steve, Wanted to give you an update. Actually had to drive the car the next after we spoke but I felt that since I was tearing it back down again anyway I would just keep an eye on everything, I wasn't going that far. Got home and waited for the engine to cool down and retourqued the head nuts and low and behold I now have no leaks.... no evidance of leakage at all. However, I am still using oil at an alarming rate. I suspect it is from the weber two barrell carb creating too much draw on the side vent. I have zero spots on the floor of the garage. Thoughts? |
| Peter Murray |
| Peter- Weber DCOE or DGV? Where on the intake manifold is the crankcase vent hose attached? How do your spark plugs look? Lottsa black carbon on the insulators? |
| Steve S. |
| Steve, In answer to your questions (as you posed them) Weber DGV. The vent hose is connected to the air filter, (see pic) and the plugs look OK the last time i had the head off. I was however scraping carbon off the head while it was exposed. Sorry, MGE won't allow me to post the photos. They are two large. I can send them to a seperate address if you would like. Thanks |
| Peter Murray |
| Peter, there are photo programs out there that make shrinking pics to a more reasonable size really easy. |
| Tom |
| Peter- If your spark plugs were OK then the oil probably isn't being drawn into the combustion chambers. However, to diagnose further, we need to know which engine it is that you have. |
| Steve S. |
| Steve, The engine number on the left side of the block reads: 18V890AEI01039, hope this helps. |
| Peter Murray |
| Peter- OK, your engine number indicates that it should have the most effective oil mist condensor of the B Series engine, plus you say that your spark plugs are reasonably clean. I doubt that the oil is going into the combustion chambers. Any signs of leakage? Check the tappet cheat covers on the carburetor side of the engine (under the exhaust manifold). Over time the gaskets there usually go bad from the heat of the exhaust manifold. Also, check the drain hole in the bottom of the clutch bell housing. It should have the prongs of a cotter pin sticking out of it. While you're down there under the car, take a hard look at the sump plug and the sump gasket for signs of leakage. |
| Steve S. |
| Steve, I just got done replaceing the trans and while there replaced all gaskets and washers I could find, including those you mentioned. I do nott have a leak and there is no evidence of any oil under the car from the cotter pin or else where. That was why i was thinking it was being drawn into the carb throat. I will get a program to downsize my photos and get them to you. Thanks in advance. |
| Peter Murray |
| Steve, Wanted to continue this dialog by saying that I removed the hose from the vent on the side of the engine and allowed the vent to breath into the engine compartment unassisted by the pull from the carb...I used no oil today and I traveled more than 250 miles. So that kinda confirms for me at least that the draw from the carb is too great BUT can I drive with the vent, venting into the engine compartment? I did not notice any residue of oil anywhere. |
| Peter Murray |
| If it were too much suction on the front tappet chest cover there would be oil in the hoses and the air filter. But it is very hit and miss whether this type of ventilation does anything anyway, really with a Weber on a carb that was originally carb ventilated you should fit a PCV valve. Having said that I can't explain why it should use so much with it connected and none with it disconnected, I'd like to see more runs with it connected and disconnected before being certain that is the cause. With an open port the engine can suck in dirt and moisture, at the very least it should have a filter on it. What have you got by way of charcoal canister, its plumbing and oil filler cap? |
| Paul Hunt2 |
| Okay Paul, Seems we lost Steve somewhere along the way. I ran it again today for approx. 100 miles and had a little oil loss, 1/8 of a quart maybe. Again I was running without the vent connected to the carb. Today was much more start and stop however. I should mention I have removed all smog from this car and in turns of the canister, I have the vent from the valve cover connected to it however i do not have any of the other components connected. The filler cap is stock and does not appear to be leaking. While writing this i decided to check the condition of the hose from valve cover to canister and it has oil running out of it....that can be a source of some of the loss I now suspect. Can anyone fill me in on the cannisters use with out all the other components connected? Thank you |
| Peter Murray |
| Peter- You should leave the vacuum line ho0oked up to the induction system. Without the partial vacuum induced by this system, the pressurized gases inside the crankcase of the B Series engine would cause oil on the cylinder walls to be blown past the piston rings into the combustion chambers, leading to carbon buildup on the roof of the combustion chambers as well as on the piston crowns, and consequent preignition problems. The carbon can also collect in the groove provided for the compression ring, causing the ring to seize (Bet’cha can’t guess how I know this!). In addition, an excess of these pressurized gases and oil mist would also be vented partially through the breather tube of the rocker arm cover. In the case of 18GJ, 18GK, and 18V engines equipped with a nonvented oil filler cap (BMC Part # 13H 2296), rather than allowing oil to travel down through the pushrod passages in order to aid in the lubrication of both the balled lower ends of the pushrods and the upper sections of the tappets as they should in both cases, pressurization of the fuel tank as well as the adsorption canister would occur, interfering with its function. A seemingly incurable seeping leak at the base of the rocker arm cover is the usually the first external symptom in such cases. Oil in the hose (pipe) that connects the rocker arm cover to the canister would be an internal symptom of the occurance of this event. In order for the excess pressurized gases in the crankcase to arrive at the rocker arm cover, they would also have to travel up the past the pushrods and the oil drainback holes that are located in the floor of the tappet chest. This means that the excess pressure of the gases would be forced upward around the tappets, decreasing the additional lubrication supplied by both the oil mist from the crankshaft and the oil that runs down the pushrods from the rocker arm assembly onto the upper sections of the tappets. The pistons would also have to work against the pressure trapped inside the crankcase, retarding their downward movement (i.e., “Pumping Loss”), thus causing more combustion heat to the transferred to both the cylinder walls as well as to the roof of the combustion chamber, making the engine run hotter and reducing power output. Thus it must be understood that all of this is prevented by drawing all of the pressurized gases inside the engine out through the front cover of the tappet chest and into the induction system under the effect of an induced vacuum, and as such, the system contributes to long-term reliability and a prolonged engine lifespan. |
| Steve S. |
| Steve, I am rereading your last post and I have one question for the moment. I hope I get this right, On the right front side tappet cover is a vent pipe that SHOULD stay connected to the intake "system" in some fashion to relieve gases built up in the oil pan, correct? I may not have imparted all the info you need to make your diagnoses. I have the afore mentioned 18V engine, with an aluminum head and all smog removed. When I first got the car it had a secondary aluminum non-vented valve cover on it which I had difficulty keeping leak free. I changed it to a standard vented cover. Running the car for the last few days with out the hose from the side vent connected to my air cleaner and with the valve cover vent plugged, I have had no loss of oil. |
| Peter Murray |
| Peter, I'm not Steve, but I'll go ahead and throw in here in hopes that it may help. Yes, the tappet cover vent is often connected to the intake system, but it is done in a controlled fashion. The control is normally a PCV valve in older engines, but things get more complicated on newer engines. It sounds like all the stuff to do this has been removed from your engine. Also, the path for the air into the engine is controlled. It seems that may also have been removed or altered on your engine. The object is to make air pass through the engine to reduce crankcase pressure and vent bad gasses that you don't want in the crankcase, and then to vent them to the intake system in a manner that does not disrupt the other functions of the intake system. In the older models this was done with a small hole letting air into the valve cover, and a PCV (positive crankcase ventilation) valve that sat on the intake manifold, and was connected to the tappet cover. This PCV valve, and the small hole in the valve cover, limited the air that would be sucked through the engine by the intake manifold. So, from an earlier post, here is what I did to my 71 GK engine. This is for an earlier engine, but with the removal of the emission control system, your engine is more like an older one now: When I got my car it had no canister, no PVC valve, no venting in the aftermarket aluminum valve cover, and the valve chest vent was open. I solved the problem by adding a mushroom type PCV valve [to the intake manifold], and drilling and tapping the oil cap. Then I brazed a small brass fitting shut, drilled it to match the vent on a stock valve cover, screwed it into the cap, and ran a hose from it to a separate filter. I hope this makes some sense. It looks easy if you could see it, but I don't have a working digital camera at the moment. Charley |
| C R Huff |
| Peter- Yes, the crankcase venting from the front tappet chest cover should be connected to the induction system in order to vent the gases from the crankcase. Charley has it right when he says "The object is to make air pass through the engine to reduce crankcase pressure and vent bad gasses that you don't want in the crankcase, and then to vent them to the intake system in a manner that does not disrupt the other functions of the intake system". |
| Steve S. |
| OK, so...if the gases are removed from the crankcase and induced into the intake system in a manner not conducive to the operation of the system....maybe it is "pulling" to much and bringing oil with it? wouldn't that show in some fashion out my tail pipe? Also, since I have a vented valve cover should i leave that vented or not vented as it is today? |
| Peter Murray |
| Peter, I would not assume that you would see it out your tailpipe. You can burn a lot of oil and not see smoke. I think you said that your car had a Weber downdraft and manifold put on it. So, for me it is just a guessing game. Do you have a port in the manifold that you can use to install a PCV valve? If it were mine, I would try to add a PCV valve to the manifold. Maybe it can be drilled and tapped? If you can mount a mushroom type PCV valve to the manifold, and connect the other end to the valve chest breather tube, the job is half way done. Then, do you mean that you have a stock valve cover with a vent? I don't know on the newer ones, but on the older ones this is a curved tube with a restrictor in the end of the tube. That tube needs to be connected to a filter or the charcoal canister, and you would then use a non-vented cap. If you don't do this right, you can just suck too much air into the manifold, which will lean out the fuel/air mixture, and may suck oil out of the engine. Charley |
| C R Huff |
| CR, I think you may be on to something. I had the curved tube with restrictor taped shut for a few days and removed the hose from the vent/flame trap pipe. I DID NOT BURN/USE ANY OIL. Today, I reconnected the curved tube to a hose, opening it but not connecting it to the charcoal canister and again left the vent/flame trap pipe unconnected and I used almost a pint of oil. Do you think I can go back to my after market aluminum non-vented valve cover and eliminate the charcoal canister all together? Lastly, I do have a port in the intake manifold which has the line from the brake servo connected to it. Can I run both vent/flame trap and brake servo off the same hole? I believe I can make that work with out drilling and tapping. I will also try and send you a photo of my set up. Thanks to all for all your help. |
| Peter Murray |
| Peter- I presume that by a "vent" you mean a tube on the rocker arm cover that points to the rear of the engine compartment. Its function is not to perform as a vent, but as an intake. If this is what you're refering to, check the tube to be sure that it has a 5/64" restrictor press-fitted into it. This should be eitherattached by tubing to a carbon canister, or a small filter fitted onto it. |
| Steve S. |
| Steve, Yes i mean that small curved tube pointing to the rear of the engine compartment. When I had it closed off I was not using oil. I opened it today and did not run it to anything except a hose , left to dangle in the engine compartment and I used a pint of oil. I do not have ANY of the other SMOG components attached to this engine and I was wondering if I NEED to maintain that one or remove it all together? |
| Peter Murray |
| Peter, Short answer on using the brake vacuum port in tandem with your tappet chest vent is I don't know. But, I'll go ahead and guess anyway. I think it may be okay, but if I were doing it, I would vent the tappet chest closer to the manifold and the brake farther from the manifold. In other words, like a stacked arrangement. I think that would reduce the chance of having oil vapor migrating up the hose to the brake booster. Also, don't forget that the tappet chest can't be connected to the intake manifold without a PCV valve in between or it will suck too much air out of the crankcase. As for the valve cover end, you didn't answer Steve's question about the restrictor button yet. I would not remove the charcoal canister without contemplating what that will do to your gas tank/fuel system. You might be opening another can of worms. You can use the unvented valve cover, but only if you use a vented cap. You have to end up with two vents; one in and one out. The in vent is controlled by the restrictor button (or something performing the same function) and the out vent is controlled by the PCV valve. However, if you use the non vented cover, you need to consider what air stream will purge your charcoal canister. I haven't owned a model as new as yours so I never had to figure that system out. It probably purged through stuff that is already missing from your car. Charley |
| C R Huff |
| Yes, that hose dangling from the rocker arm cover does ideally need to be attached to the Original Equipment charcoal canister. The charcoal canister then needs to be hooked up to the vapor condensor for the fuel tank (its located in the boot). Perhaps somebody who has desmogged his engine has a charcoal canister that you can get. If you can't get the necessary hardware that is needed for this task, then simply install a small breather filter in place of the hose. |
| Steve S |
| I want to thank you all for all your help. |
| Peter Murray |
This thread was discussed between 26/04/2008 and 15/05/2008
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