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head bolts


David K

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I have a set of turbo head bolts from MSA i will possibly use to put together my build. Im not sure, as i was also thinking of using head studs. Ive been a big fan of studs ever since i used them to attach my header on the black z a while back. I just kept tightening and tightening, and i got the header on there real nice.

 

I got curious today and took out an old set of head bolts that came from a very old warped engine. I took turns dropping each one of them from my chest line. A few of them made the same sound, the others all had a sound of their own. Some vibrated long, and the few others made a dinging sound on drop and went quiet. About 5 of the old head bolts sounded like the new turbo headbolts i have. Does this mean some of the head bolts i was experimenting with are bad?

 

I understand they may expand over time, and during overheating situations. Should they all sound the same upon dropping them? Thankfully my turbo head bolts havent been in an overheating situation, and i know they are ok for use in a rebuild.

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  • 2 weeks later...
Guest Zcarsmakemyheadhurt

In most cases you can reuse the head bolts. I don't know how accurate your scientific testing is but I would use the new units and disgaurd the bolts from the warped engine.

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How different is the sound? If there are a lot of additional harmonics present (i.e., the part 'buzzes') in the tone, I would say there is a definite possibility of problems. Otherwise, it's hard to say.

 

I am a bit concerned with the testing method, though. What kind of surface are you dropping the bolts on, and how far are you dropping them? You can generate amazingly high local accelerations by dropping a hard part on a hard surface. For instance, a 1 meter drop to a concrete surface can generate several thousand g's of instantaneous acceleration (the number that sticks in my head was 20k g) in a test like that.

 

I'd be a bit worried about causing local damage to the threads or elsewhere on the bolt by using this method, which could effect either the torque/clamping force relationship or the overall strength of the part. I know it sounds stupid at first, but high tensile strength parts like that can be pretty brittle.

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I think there may be some problems with your testing method. Depending on how the bolt hits the floor, it will vibrate at a different frequency. Hence the sound difference. If you are pondering using studs, do it. Studs are a much much better fastening system than bolts, and I am sure every automaker on earth would use them if the cost was less than bolts, but it isn't. If you are building an engine you want to keep, studs are good!

 

If you are going to use bolts, get new ones, unless it is a JY engine that you are just throwing together. (which I've done, and reused head bolts with fine results) If you are looking to make some power though, I'd be wary.

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Guest pintoz

Regardless of the testing method, hearing pings and vibrations would tell me that the properties of the metal have been compromised. I've been told that once you pop the bolts off, you should always replace them. Under the initial torque and the additional heating and cooling of the block, you can't guarantee the same grade bolt that you started with.

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