Head Bolts..Reuse or buy new ones?

[Banzaiii67]

There seems to be differing opinions. Some say they stretch, other say they have been reusing them and torquing to spec for years. What say you ?

 

[super-bee_ski]

They are so cheap
Just replace them.

 

[Herr_Poopschitz]

All bolts stretch, that's how they work. The question is whether they've stretched too much (yield) - this makes them worthless.

Unless you know their history, good idea to replace.

 

[Coyoteduster]

Replacing them is cheap insurance ...

 

[Garys1969RR]

I have re used them many times with no probs. Goin to Alum heads now, they require a bolt with a small head. About $80 shipped from 440 source. I will re use these too if necessary.

 

[Dako]

Machine shops have rebuilding motors and re-using bolts for years...unless of course, threads are buggered up or heads are rounded. Are you upping the compression/ hp significantly? Are you going to be topping it out at the track regularly? If not, well...it's your money. Put it where you see fit.

 

[brasil]

Alwys reused the head bolts..... never bought new ones in my life. If the threads are good no problem in my opinion...

Greetings Juergen

 

[69Bee]

Reuse unless damaged or stretched. This is unless you are talking about Torque-to-Yield head bolts, in which case you replace them each time of course.

 

[Banzaiii67]

Reuse unless damaged or stretched. This is unless you are talking about Torque-to-Yield head bolts, in which case you replace them each time of course.

These are just stock bolts, someone where between 1968-1973 vintage as I had one 346 head and one 906 head. I think I'm just going to replace them, they were a bit over torqued from when I removed them.

 

[67Satty]

All bolts stretch, that's how they work. The question is whether they've stretched too much (yield) - this makes them worthless.

Unless you know their history, good idea to replace.

I have a Moto Guzzi motorcycle that calls for the heads to be retorqued for every valve adjustment (which is every 3.000 miles).

By that logic, I should be replacing the head studs every 3,000 miles (or at least after a certain number of retorques) because to retorque the heads properly, the manual calls for me to back off the nuts first. I don't know of any Moto Guzzi or BMW airhead owner that replaces their head studs on a regular basis or after a certain number of cycles of retorques of them. Or does a stud not stretch and a bolt does?

If someone could give me a good reason to not reuse head bolts that don't have messed up threads other than "what's another $70-$80" I'd be all ears.

 

[Cranky]

The old school head bolts are not torque to yield so they can be re-used if they were not over torqued in the past. If they were, you can usually see it but they are going into cast iron and if they are over torqued enough, they will usually mess up the threads in the block and the flat on the head will usually tell you something too. 'Pulling' the threads in cast iron is not particularly too difficult to do. Another factor would be rolled vs cut threads. Are factory head bolts rolled? Can you tell by looking? Rolled threads are generally smoother and cheaper than cut threads but to the naked eye, it's hard to tell. Anyways, I re-use my head bolts so long as they are in good condition and anything that's going to be used for extreme duty will get studs instead.

 

[miller]

Yeahh, cranky!

Bolt is a bolt? Hell no. Depends on where it was made. And how it was made.

Mopar bolts were usually the best materials, at least in the olden days. Unless there's something wrong with a particular bolt, have no fear re-using it. Even if stretched a minor amount, it's still a tougher bolt than any, unless you want to pay top dollar.

It's your money...you decide why you want to spend it. These so-called 'hi-tech' bolts you can buy all day long are simply money-makers, for those selling 'em.

 

[Herr_Poopschitz]

I have a Moto Guzzi motorcycle that calls for the heads to be retorqued for every valve adjustment (which is every 3.000 miles).

By that logic, I should be replacing the head studs every 3,000 miles (or at least after a certain number of retorques) because to retorque the heads properly, the manual calls for me to back off the nuts first. I don't know of any Moto Guzzi or BMW airhead owner that replaces their head studs on a regular basis or after a certain number of cycles of retorques of them. Or does a stud not stretch and a bolt does?

If someone could give me a good reason to not reuse head bolts that don't have messed up threads other than "what's another $70-$80" I'd be all ears.

I'm not sure what 'logic' you're referring to, or why you quoted me in your post. Unless you mistook 'too much' for 'too often'...which wouldn't make sense cuz I said 'yield'...unless you don't know what 'yield' means...? Please explain the rationale.

This is the best way I can explain the mechanics of threaded fasteners:

Stress-strain curves are what a person should reference for whatever material is in question. All bolts and studs stretch when torqued (rod bolt stretch gages, for example...yes?). This stretch and the material's 'desire' to return to its original length, as long as it's still in the elastic range in the stress-strain curve, is what provides what some call 'clamping force'. If the material is forced into the plastic range, past yield, the material will never return to its original shape/size, ie, a fasteners ability to clamp goes down the toilet. Easy way of saying it is 'overtorque, throw them away'.

The internal stresses are different between a bolt and stud. Bolts see stress both due to torque and stretch. Studs only resist stretch. Again, rule of thumb, overtorque either and it's trash.

Hope this makes sense.

 

[bigblock]

Any bolt or a stud is a spring. After a million hot and cold cycles it,just like any spring, wears out. I,along with many others,have reused them with success. It is best to replace them.

 

[miller]

Just a matter of preference. And dollars.

Just me, okay? I've never replaced a engine bolt yet, unless it was busted, bad threads, or the like. Can't remember ever needing to.

At least any motor 70, or older, you know those bolts were made right, for the job they do. Sure, gotta consider the number of times they've been re-used, and what the motor is used for. If you only re-built every 100,000 miles, or 1/4 mile.

Pick your poison.

 

[rev.ronnie]

If you're not going to replace them with a high quality, American made set, I would re-use them. A stock head bolt, made in the USA 40+ years ago, is a high quality piece. Steel was good, corners weren't cut.
If the stock ones are in good shape, not corroded or damaged, I would use them in a heartbeat over some Chinese knockoff.

 

[Rocketman]

My Edelbrock Top End Kit came with new bolts, I plan to use them this week.