LOST JEEPS :: View topic - Loose cylinder head bolts.

My head was cracked but it had never overheated.
The cracks were around the exhaust valve seat areas of cylinders 2, 3, and 4.

Although I'm sure heat was a factor, AFTERMARKET EGR AND TERRIBLE PROGRAMMING FOR THE ECM WERE PROBABLY BIG FACTORS

flash7210 wrote:

Fixed it for ya!

I felt that if the factory had included the washers that the head was clearly designed to have (considering the recesses milled into it) the force would be spread out enough to avoid the crushing effect. I'm no engineer however.

Mike92104 wrote:

I am an engineer, and I agree with you to some extent.
Better to say that " the head clamping force would be distributed enough to prevent local
yielding of the head and resulting galling of the recesses," but that is being picky.

Your basic point is on target.

In the case of overheating the engine, consider the overall surface areas involved - The head is limited to the 4" circle of the actual cylinder, and much less so of the rest of the flat surface area. The block, meanwhile, has the entire inner surface of the piston sleeves to transfer heat, and presumably some water contact on the back of the sleeves to move that heat away to the block iron.

The heat in the iron will translate most effectively into the bolts which are in direct contact and closely adjacent to the cylinder heat, where the head has some insulation potential from the head gasket's layers to protect it. The bolts would expand and or potentially change their metallurgical properties - this is why I believe the bolts weaken over time. Continual heat cycling eventually weakens the steel enough that they stretch out or actually rotate in place.

I have worked on many of these now - None (thankfully) with a cracked head or block, but MANY with loose bolts in a variety of positions. Read through the research thread and see the results people have posted for yourself - The numbers aren't as important as the differences within in the same engine. They should all be roughly the same numbers, not all over the map with 40+ pounds of a range!

Author:	lacabrera [ Mon Sep 14, 2015 6:26 am ]
Post subject:	Loose cylinder head bolts.
My opinion. If and when this engine over heats the aluminium head will expand more than normal and pressure around the bolts will cause the head to collapse causing a less torqued bolt or worst a cracked cylinder head. The aluminium head is weaker than the factory bolts. The only cure is a redesigned cylinder head or just don't let the engine overheat?

Author:	Mike92104 [ Mon Sep 14, 2015 1:23 pm ]
Post subject:	Re: Loose cylinder head bolts.
I felt that if the factory had included the washers that the head was clearly designed to have (considering the recesses milled into it) the force would be spread out enough to avoid the crushing effect. I'm no engineer however.

Author:	flash7210 [ Mon Sep 14, 2015 2:14 pm ]
Post subject:	Re: Loose cylinder head bolts.
My head was cracked but it had never overheated. The cracks were around the exhaust valve seat areas of cylinders 2, 3, and 4. Although I'm sure heat was a factor, stress and poor casting by manufacturer are the most likely causes.

Author:	Hexus [ Mon Sep 14, 2015 2:18 pm ]
Post subject:	Re: Loose cylinder head bolts.
flash7210 wrote: My head was cracked but it had never overheated. The cracks were around the exhaust valve seat areas of cylinders 2, 3, and 4. Although I'm sure heat was a factor, AFTERMARKET EGR AND TERRIBLE PROGRAMMING FOR THE ECM WERE PROBABLY BIG FACTORS Fixed it for ya!

Author:	flash7210 [ Mon Sep 14, 2015 7:38 pm ]
Post subject:	Re: Loose cylinder head bolts.
Hexus wrote: flash7210 wrote: My head was cracked but it had never overheated. The cracks were around the exhaust valve seat areas of cylinders 2, 3, and 4. Although I'm sure heat was a factor, AFTERMARKET EGR AND TERRIBLE PROGRAMMING FOR THE ECM WERE PROBABLY BIG FACTORS Fixed it for ya! I think we all can agree that the EGR valve is bad for this engine, but I dont think the EGR was a factor in my case. My EGR has been disabled/blocked for the last 100k miles. And the factory ECM programming, while not as good as a GDE tune, is not terrible. Its just typical of averge factory tuning.

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Author:	LMWatBullRun [ Tue Sep 15, 2015 6:50 pm ]
Post subject:	Re: Loose cylinder head bolts.
Mike92104 wrote: I felt that if the factory had included the washers that the head was clearly designed to have (considering the recesses milled into it) the force would be spread out enough to avoid the crushing effect. I'm no engineer however. I am an engineer, and I agree with you to some extent. Better to say that " the head clamping force would be distributed enough to prevent local yielding of the head and resulting galling of the recesses," but that is being picky. Your basic point is on target.

Author:	Mike92104 [ Tue Sep 15, 2015 7:00 pm ]
Post subject:	Re: Loose cylinder head bolts.
LMWatBullRun wrote: Mike92104 wrote: I felt that if the factory had included the washers that the head was clearly designed to have (considering the recesses milled into it) the force would be spread out enough to avoid the crushing effect. I'm no engineer however. I am an engineer, and I agree with you to some extent. Better to say that " the head clamping force would be distributed enough to prevent local yielding of the head and resulting galling of the recesses," but that is being picky. Your basic point is on target. Thanks for translating. Mike

Author:	geordi [ Tue Sep 15, 2015 8:32 pm ]
Post subject:	Re: Loose cylinder head bolts.
In the case of overheating the engine, consider the overall surface areas involved - The head is limited to the 4" circle of the actual cylinder, and much less so of the rest of the flat surface area. The block, meanwhile, has the entire inner surface of the piston sleeves to transfer heat, and presumably some water contact on the back of the sleeves to move that heat away to the block iron. The heat in the iron will translate most effectively into the bolts which are in direct contact and closely adjacent to the cylinder heat, where the head has some insulation potential from the head gasket's layers to protect it. The bolts would expand and or potentially change their metallurgical properties - this is why I believe the bolts weaken over time. Continual heat cycling eventually weakens the steel enough that they stretch out or actually rotate in place. I have worked on many of these now - None (thankfully) with a cracked head or block, but MANY with loose bolts in a variety of positions. Read through the research thread and see the results people have posted for yourself - The numbers aren't as important as the differences within in the same engine. They should all be roughly the same numbers, not all over the map with 40+ pounds of a range!

Author:	Mike92104 [ Tue Sep 15, 2015 10:34 pm ]
Post subject:	Re: Loose cylinder head bolts.
I'm not sure how much value the data on the head bolts has. There's no way to factor out all the different variables that might make a bolt easier/harder to remove. I'm sure just doing them in a different order from each engine to the other would produce different results.

Author:	geordi [ Wed Sep 16, 2015 12:01 am ]
Post subject:	Re: Loose cylinder head bolts.
The order shouldn't change anything, especially if the studs are being done one-at-a-time and not removing all of them at once. The head will not flex with just one bolt extracted, and once the stud is torqued, that portion of the head is just as static as it was before the change. The important data is not the number, but the difference from one bolt to the next in the same engine. This is also why the variations and statistical noise can be accounted for - because we aren't interested in the actual torque which would involve certifying each and every wrench and technique... But if only the delta is valued, then the technique and accuracy of the wrench can be assumed to be "accurate enough" when considered FOR THAT ONE ENGINE and none other. After doing so many of these, I consider a delta of 10-20 lbs as statistically identical and not significant... But a delta of 40+ lbs, THAT is above any of these isolated variables, can we agree? Reasonably, there should not be such a wide variance if they were all installed the same way. (Which is an assumption yes, but should be safe because it is how they are supposed to be installed by the book) Assuming that the factory would have done the proper process the same way on each and every engine... Then the numbers should track... But they aren't. If every vehicle is built in the same way at the same points of assembly, then the major variances are climate of the owner, driving style, load / towing, mileage... But we can't calculate those out easily. That is why I don't care about the actual torques, just the delta. Delta says bolt X and bolt Y which both received the same of all those other factors should be the same... But if they aren't, then why? THAT is what I am researching to discover.

Author:	LMWatBullRun [ Wed Sep 16, 2015 12:00 pm ]
Post subject:	Re: Loose cylinder head bolts.
The order of the bolt removal will not be significant IF the head and block are both flat. If the head is warped then the order of removal could make a big difference is removal torque. I do agree that the delta is much more significant than the reported torque. Looking at the differences really tells the tale. MY hypothesis is that minor head warping leads to HG leaks, which lead to local overheating, which leads to MORE head warping and possibly cracking, and the cycle continues to failure without intervention (ARP studs). The factory head bolts do not have enough bearing to prevent local yielding of the head bolt recess surfaces. This explains all the observed phenomena with this engine, I think, in particular the distribution of HG leaks.

Author:	lacabrera [ Wed Sep 16, 2015 12:38 pm ]
Post subject:	Re: Loose cylinder head bolts.
geordi wrote: In the case of overheating the engine, consider the overall surface areas involved - The head is limited to the 4" circle of the actual cylinder, and much less so of the rest of the flat surface area. The block, meanwhile, has the entire inner surface of the piston sleeves to transfer heat, and presumably some water contact on the back of the sleeves to move that heat away to the block iron. The heat in the iron will translate most effectively into the bolts which are in direct contact and closely adjacent to the cylinder heat, where the head has some insulation potential from the head gasket's layers to protect it. The bolts would expand and or potentially change their metallurgical properties - this is why I believe the bolts weaken over time. Continual heat cycling eventually weakens the steel enough that they stretch out or actually rotate in place. I have worked on many of these now - None (thankfully) with a cracked head or block, but MANY with loose bolts in a variety of positions. Read through the research thread and see the results people have posted for yourself - The numbers aren't as important as the differences within in the same engine. They should all be roughly the same numbers, not all over the map with 40+ pounds of a range! I carried out a test on an old head using a set of factory bolts, the head is far weaker than the bolts, I think the chance of them rotating and becoming loose is almost impossible in a non rotating environment. Washers under the bolts with enlarged recesses may help to some degree.

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