Question about head bolts

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jhdeval

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Okay so my question is can/should you reuse the head bolts? If not why?

I ask this question because last week I was watching the "power block" and one of the shows talked about bolts that should be replaced if they ever get removed. They indicated the head bolts was one of those. They cited that when you torque a bolt down it stretches the threads of the bolt. I do see how that could be an issue but I do not understand what problems it could cause.
 
Stock head bolts? I reused mine with no issues. It does in fact stretch the threads that's how they have their clamping/torque specs. I just made sure the holes were clean and inspected the bolts and reused them.

The problem it causes is it could change the actual torque number.
 
Some manufacturers use torque to yeild bolts that should be replaced everytime.
 
I would run a nut on the original one and see if you feel any wiggle or to tight on the threads, I don't trust after market graded bolts, But thats just my thoughts, I have rebuilt at least 8 engines and always reused head bolts.. never a problem.
But it is posable, anyone could have over tightened them at one time, worth cleaning and checking them first.. JMO.
 
Badsport said:
Stock head bolts? I reused mine with no issues. It does in fact stretch the threads that's how they have their clamping/torque specs. I just made sure the holes were clean and inspected the bolts and reused them.

The problem it causes is it could change the actual torque number.
Click to expand...

memike said:
I have rebuilt at least 8 engines and always reused head bolts.. never a problem.
But it is posable, anyone could have over tightened them at one time, worth cleaning and checking them first.. JMO.
Click to expand...

same here, ive always re-used mine on my stock re-builds
 
It is more an issue with modern engines using aluminum heads or block. Post #4 was right on the money about the terminology. Consider that aluminum has different thermal expansion characteristics than cast iron. Newer engines need bolts that can stretch and contract with the components and still retain their clamping force. Usually a torque to yield fastener will have a torque of something like: torque all bolts to 30 ftlbs, next torque all bolts to 60 ftlbs, next retorque all bolts to 60 ftlbs, and finally tighten bolts another 90 degrees. Of course this is all in the proper torque sequence with the proper lube or lack of lube.
 
Hears my two cents, Yes they do stretch & its prob best that you don't reuse them if the heads have been off befour, but if your taken it off for first time, then I say reuse them one or maybe two times, but if your putting togeather something to race, I would say never reuse them.
 
Most people and shops re-use the head bolts on older cast-iron head engines thru the 1980's. I doubt the metal yields at the torqued limits, so if not rusty should be fine. As a technical point, the tension you get in a bolt from a given torque depends on several things. I have dealt with that many times in my day job. Studies show that using mineral oil on the threads and bolt head does not change the tension and only gives more consistent results. High-pressure grease or dry MbS2 lube is a different story (~2x more tension). Don't use that or you may yield or break a bolt before torque wrench clicks. If you use oil, just a few drops. Don't fill the holes or you can get hydro-lock and false readings.

Some "torque to yield" bolts, common in modern cars, allow re-use if the diameter of the bolt exceeds a minimum value. The special flexplate bolts in my Mercedes are like that. My 1996 Mopar 2.4L manual says not to re-use the "torque to yield" head bolts, but I did so anyway when swapping their defective head gasket at 39K miles for the new MLS design. Now at 188K miles and still no problems. But don't follow me unless you are a true CMB.
 
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