Is there anyone that has reused old head bolts on new heads. :confused:

 

The largest Corvette dealer in Dallas said they do all the time. :(

The bolts are torque-to-yield (they stretch) and should not be reused under any circumstances.

 

NEVER use same head bolts. ALWAYS use new head bolts EVERY TIME you change heads.

Also, consider using aftermarket ARP bolts. Expensive in the short-run, but cheap insurance in the long-run. Just my .02 cents.

Gary

 

I would not reuse head bolts..
I have a set of ARP studs on order, I'll let you know how it goes.


[Modified by Wt99C5, 2:55 AM 10/14/2002]

 

:nonod: :nonod: :nonod:

 

I wouldn't want to lose a motor for the price of a few head bolts. Since they are torque to yield, I'd bet money that you would have some pretty uneven clamping force across the entire head surface if you reused the bolts. Just don't use studs, or you will never be able to pull the passenger side head off with the engine in the car :yesnod:

 

I am curious, I have heard and saw in many posts that the head bolts are torque-to-yield .

But is it really so??

I myself have looked for info in my GM service manual nothing there.

Don't get me wrong I think using new bolts is a great idea if you want to spend the money.

Still, I would like someone to show me proof. This is not to flame anyone, it's just....well have you ever heard of people repeating some inaccurate info enough times that everyone thinks it's fact.

Steve Murray, he is the local corvette wrench turner at my Chevy dealership.
He and the manager say they are not torque-to-yield bolts.
In fact they claim that GM has issued a bulletin that under warranty issues where the head bolts are to be removed, that are not to be replaced but cleaned and reused.

And think about this, some of you may be old gear heads, but in the past I have used new rod bolts that were torque-to-yield. You would use a special tool with a dial-indicator on one end. It was shaped kind of like a c-clamp. The rod bolt had an indention in each end of it, the solid pointed base of the c-clamp would fit in one end and the pointed end of the dial-indicator would go in the other. Then you would torque the bolt until it stretched “x” amount measured by the dial-indicator .

These head bolts can not be measured in this fashion, torque-to-yield implies that you apply “X” amount of tightening until it stretches the desired amount.

What I’m trying to say is, I am not 100% sure they are not torque-to-yield, but every thing I have found and come across including personal experience does not jive with this claim.

“Well this ought to stir the pot”

Operations

 

......... :yesnod: Very good insurance.............. :yesnod:

 

For what is cost why take a chance with it. The negative is to awful to think about.

 

Mike - Here are a couple of excerpts from my 2001 service manual page 6-90:

"Important: The M11 cylinder head bolts are NOT reusable."
"Discard the M11 cylindehead bolts."
"Important:
• Do not reuse the M11 cylinder head bolts. Install NEW M11 cylinder head bolts during assembly."

The M11 are the 10 around the cylinders. The 5 M8 bolts across the top of the head are reusable.

 

Thanks for putting that info in, but do you know if they are truely torque-to-yeald?

 

I would do new ones.

 

Apsolute best choice is the ARP stud kit, particularly if you EVER plan to put a blower on your vette!!!!! Even if you don't tourqing heads with studs is better than bolts - look at the big boys, they all use studs!!! CHEAP INSURANCE!

JR :yesnod: :yesnod: :yesnod: :yesnod: :yesnod: :yesnod: :yesnod:

 

Mike - I haven't found an explicit statement that the bolts are tty, but the torqueing procedure suggests they are. The M11 are first torqued to 22 lb-ft then 2 sequences of 90 degrees using a "torque angle meter." (the 2 short M11's get 50 degrees on the final pass.) Here is an interesting link on tty headbolts.
http://www.federal-mogul.com/felpro/...kets/pg_9.html

Alan :seeya

 

I reused mine, and with over 6K miles since the addition of the heads (with quite a few of them hard) I have zero problems. I talked with a tuner that had reused them on his car, so I felt that was good enough for me.

 

Not flaming or trying to "stir the pot" at all here... just trying to learn. Could you ask your GM tech friend for a copy of that bulletin? I'd like to see that it posted if possible:)

What I would like to know if they are not torque-to-yield bolts why would the GM Service manual want us to torque to 22ft-lbs followed by 2 sequences of 76 degree turns (except upper outside bolts getting 34 degrees in their last sequence)? Why such exacting numbers? Why bother with using a degree wheel? Why not just torque them all to, say, 65 ft-lbs and be done with it? Could it be that GM engineers know that these bolts will stretch an acceptable average if you follow their detailed torque and degree sequence? Same with the crank bolt... I've often wondered what exactly the ft-lb of torque winds up being AFTER I torque the bolt 240ft-lbs and then turn it an additonal 120 degrees. All I know is in the past we had broken many a 1/2 inch drive tools trying to accomplish 120 degrees after 240 ft-lbs. We have since stepped up to 3/4 drive. The manual then states to remove the bolt you just tightened that amount and install a new bolt, tighten to 40 ft-lbs and then crank it another 120 degrees. Surely, this must mean torquing to yield. No?

All I know is we follow the book to the letter when performing major engine maintenance (any maintenance really)... book hasn't let us down yet.

:cheers:

 

Bill - Follow the book is good advice, particularly when so much is at stake with headbolts. But I am curious about the degree numbers you quote (76 and 34). My 2001 service manual says 90 and 50. I too am trying to learn before having to learn a hard lesson through avoidable mistakes. Thanks.

Alan
:seeya

 

If I remember correctly I was quoting from a GM 97 service manual... may be different. Not trying to diminish what the engineers are trying to accomplish here but if you add up the degree's you are close to the sum either way. But, no matter what we follow the book. BTW, the 34 degree final sequence is for the 2 outter bolts underneath the valve cover. Their first sequence is 76 degrees. All the rest of the large bolts receive 2 sequences of 76 degree turns after the initial 22 ft-lb torque.... again for a 97


[Modified by billreid1@***.net, 12:11 PM 10/14/2002]

 

First of all a torque to yield (TTY) bolt isn’t really a different type of bolt. TTY refers to the technique used to tighten the bolt. When tightening a bolt, the bolt goes through three phases. An elastic phase, a plastic phase and a shear phase. In the elastic phase the bolt stretches but will return to the original length. In the plastic phase the bolt is permanently stretched. In the shear phase it breaks.

During the manufacturing process, bolts are tightened by machines that torque the bolts to a specified value and then stretch the bolts a predetermined amount based the threads per inch specs of the bolts. The goal is to get the maximum clamping force that the bolts are capable of. Done properly, the bolts will be on the edge of being permanently stretched. While it is possible to use this torque and angle method in the field, it is a method most people are not familiar with. A more practical way is to tighten to a specific torque value that will yield a clamping force within a desired range. With either method, permanent stretching of the bolt can occur and that is why they are not reused.

To reuse the bolts, you must insure that they are not permanently stretched by accurately measuring their length. If you want to spend the time and have the equipment to do so, be my guest. Otherwise, spend the paltry $66 and at least get new factory bolts.

In order to insure accurate torque readings, one should run a tap down the threads in the block to make sure they are clean so there is nothing that could influence a torque reading. In addition, the bolts should be lubricated with assembly lube to insure accuracy as well.