Doing 107 build this winter. Is there any reason to replace head bolts? One is discolored and rusted a bit. I would think any stress issues would be on the studs and not bolts. Comments?

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I would suppose if you plan to go to a higher compression motor you would need the higher tensile strength bolts.

 

Anytime they have been torqued to spec, there has been a certain amount of stretch, even on grade hardened.
Replacement is always a good idea.
I just pulled the heads on my old one ton dually and it was worth the 60 bux to replace, simply for piece of mind.

 

The problem of using used bolts is after torqueing you need to tighten
1- 120-144 inch lbs
2- 15-17 ft. lbs.
3- 90^ final tighten in same sequence
My question is why would HD recommend all this if it was not important.

I cant see how you would get the correct load with the bolt that already has the stretch gone from last time
I have read that some guys will reuse them once
I would hate to put an engine together and have a head gasket failure
That's me, I like to do it correct the first time because you will find the time and money to do it again.
My 2 cents

 

I'm assuming you mean bolts and not studs. Right?

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Why would you re-install a used, rusty bolt in a rebuild or in anything else for that matter? Not beating up on you but really this is a no brainer. Do it once and do it right.

 

I'm not saying it is the "best" practice but I have been in the Auto/truck/tractor repair business most my life (been retired a while) and can't remember replacing head bolts more than a couple times. Never had an issue? Clean them up and use them...

 

No offense taken. As I said one bolt rusted. The issue is should I just replace one or all? Money not an issue. Best practices question.

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Harley OEM head bolts are conventional type not the "torque to yield" kind. So if the bolt was properly installed and torqued in the first place, the stretch will be "elastic". That is, the bolt will return to its original length and shape when removed. So, if it's in otherwise good shape, it can be reused over and over. But the TTY bolt's stretch is "plastic". That is, it will NOT return to its original length when removed. It's permanently deformed and will not fasten properly. It could even break. That's why they cannot be reused.

 

The service manual does not call for head bolt replacement. These are very different bolts than used on older motorcycles and automotive applications. There is a stud coming up into the cylinder and the head bolt has a tube with female threads inside that goes through the head and screws on to the stud. Clean them oil the female thread and oil the flange where it contacts the head and torque them.

Rotational torque is a much better torqueing method for mating parts exposed to high heat and thermal changes in the base material.