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Approximate Head bolt torque

41K views 29 replies 14 participants last post by  Mango 
#1 ·
I'm in the process of removing my overheated head and want to verify if my threads are still good in the block. Since they're torque to yield bolts I'm not sure what torque to try. Any guesses? The last set of heads I did were on a land rover, also torque to yield, and they felt like well over 100 ft lbs, probably closer to 200. But those were some pretty big bolts.
 
#2 ·
I'm surprised this question doesn't come up more often given the number of overheated engines and problems with the threads. At 80 ft lbs. all of the bolts moved with a quick jerk, but just a very little bit. I'm not sure what that means, I think they were just clamping down more. At about 80-90 ft lbs they started very slowly and smoothly turning again, but with a lot of force. Almost like the bolts were stretching more (hopefully the treads weren't stripping) It seems like my threads might be okay assuming they would turn pretty easily if they were indeed stripped.
 
#16 ·
Listen to THIS MAN.

I just finished everything and the car runs great, probably better than before it overheated (a rebuilt vanos and a valve job helps). I skipped the time certs and the bolts held good. I couldn't really tell what the final torque was on the bolts because I was using the angle gauge on my wrench but I doubt it was more than 60 ft lbs. They all held fine though and hopefully they continue to.
They won't. A torque wrench is NECESSARY for working on any engine.

At 60 ft/lb you are at only 2/3 of the necessary torque. Would you like to have say, 2/3 of a clutch engaging? Or how about your woman 2/3 faithful?

Really man. For any serious work, you need to have the proper tools.
 
#4 ·
Your engine overheated. Before you concern yourself with bolt torque, step 1 is to have the block and head checked to see if they are warped. Re-assembling warped critical engine components is not the best idea.

If they aren't warped and you get to the stage of re-assembling the head, you must throw away the old bolts and use new bolts. Torque-to-yield bolts are designed to be used only once. Also, like wasp said, before you even pick up your torque wrench you must know what the proper torque is. Not sure why you are using a torque wrench to guess but that is completely insane.
 
#5 · (Edited)
Overheated Engine - Symptom of Major Damage

You may already have verified that major engine damage occurred as a result of the overheat (leaking head gasket etc.) However if you have not, before you take the head off follow the procedure attached for verifying major damage occurrence as a result of over heating. The Service Interpretation Bulletin (SIB) attached will help you determine if you need to get the head off and repair it. If the tube mentioned in the TSB isn't deformed or visually effected by heat, chances are your head didn't sustain significant damage (warpage).

This is just another way to determine the extent of damage before you remove a head unnecessarily.

Good luck.


BTW - In case you remove the head:

 
#7 ·
You may already have verified that major engine damage occurred as a result of the overheat (leaking head gasket etc.) However if you have not, before you take the head off follow the procedure attached for verifying major damage occurrence as a result of over heating. The Service Interpretation Bulletin (SIB) attached will help you determine if you need to get the head off and repair it. If the tube mentioned in the TSB isn't deformed or visually effected by heat, chances are your head didn't sustain significant damage (warpage).

This is just another way to determine the extent of damage before you remove a head unnecessarily.

Good luck.


BTW - In case you remove the head:

Very nice chart! Just for clarification, the bolts are to be torqued in sequence, then +90 degrees in sequence, then another +90 degrees in sequence? I could see someone mis-reading the diagram and doing bolt #1 to torque, then +90, then another +90, then moving to bolt #2.
 
#6 · (Edited)
It's definitely great to have Bentley manual for jobs like the cylinder head.
Although there are headgasket DIYs online, sometimes I can find the info I need faster in a book.

To answer your question regarding headbolt tightening:
(according to the Bentley)

Stage 1: 30 ftlbs.
Stage 2: +90 degree
Stage 3: +90 degree

As mentioned above, the head bolts are stretchbolts, they can not be reused.
 
#8 ·
To answer your question regarding headbolt tightening:
(according to the Bentley)

Stage 1: 30 ftlbs.
Stage 2: +90 degree
Stage 3: +90 degree

As mentioned above, the head bolts are stretchbolts, they can not be reused.
Are you sure it's not 30 N*m? The diagram from BMW North says 22ft-lbs which is equivalent to 30 N*m
 
#10 ·
It looks like maybe the "official" head bolt thread check is to just loosen the old bolts and then turn them the 90 degrees per the procedure, which doesn't seem all that accurate since they are old bolts and you're clamping down a warped head. I want to make really sure that the new bolts will tighten down and stay tight. I tried cleaning, oiling and then tightening all the old bolts and they all hit about 55 ft lbs on the second 90 turn. I'm surprised by how little torque that is. I then tried 70 ft lbs to make sure and they all held. I've thought about doing the timeserts anyways as a precaution but now I'm thinking if it ain't broke then don't fix it. It will be interesting to see what torque they hit with a new head and bolts.
 
#12 ·
I tried cleaning, oiling and then tightening all the old bolts and they all hit about 55 ft lbs on the second 90 turn. I'm surprised by how little torque that is. I then tried 70 ft lbs to make sure and they all held. I've thought about doing the timeserts anyways as a precaution but now I'm thinking if it ain't broke then don't fix it. It will be interesting to see what torque they hit with a new head and bolts.
I'd be interested what the actual torque is, but 70 ft lbs. seems a lot.
The 85' V8 Mercedes I just did the heads on, the headbolts only required 44 ft lbs. torque.
I wouldn't use much lubrication on the bolts though, it may affect the accuracy of the torque wrench.

Wow, finally a thread that shows the threads don't always damage in a light overheat. I overheated my engine, and scarred to do a head gasket because I'm afraid of thread stripping. Good to see that for once in this forum. And yea I agree, if it can hold the recommended specs then you'll be fine.
Once the temperature gauge reaches the red zone, it gets hot enough to damage the metal.
 
#11 ·
Wow, finally a thread that shows the threads don't always damage in a light overheat. I overheated my engine, and scarred to do a head gasket because I'm afraid of thread stripping. Good to see that for once in this forum. And yea I agree, if it can hold the recommended specs then you'll be fine.


Sent from BimmerApp mobile app
 
#13 ·
I just finished everything and the car runs great, probably better than before it overheated (a rebuilt vanos and a valve job helps). I skipped the time certs and the bolts held good. I couldn't really tell what the final torque was on the bolts because I was using the angle gauge on my wrench but I doubt it was more than 60 ft lbs. They all held fine though and hopefully they continue to.
 
#18 ·
Why would you think overheating the engine would somehow affect the threads? Aluminum melts at over 1,000F. Your pistons would have melted long before the threads would have been affected. If the threads stripped out, it's just because aluminum is soft. It has nothing to do with the engine overheating.
 
#19 ·
Hey, I grew up in Rochester! Yes, the threads pulling out of the soft aluminum seems to be the problem. It's pretty common, read the service bulletin posted earlier in this thread, it mentions needing to check the threads after overheating the engine. I would guess overheating makes things softer and out of shape, not necessarily melted.
 
#27 ·
threads should be good... block could be fffff'ed
 
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