j_martin

Taterfarm, you said it, but you just did not understand what you said.

If you exceed the elastic limit, or yield strength, same thing, the bolt will not return to it's original length. If the design were not to exceed that limit, the max allowable length would be design plus tolerance. If there's any more, (and there is) then the stretch is planned.

Torque plus turn is the only reasonable way to control the stretch and keep it within the design, as when the elastic limit is reached, torque backs off.

The reason for it, from their standpoint, is that a more malleable metal is less prone to fatigue or corrosion stress failure.

taterfarm

I do not believe that the cummins head bolts are designed to exceed the elastic limit where they would enter that malleable stage. that is what a TTY torque to yield bolt does and these bolts are not TTY bolts

I believe that when you remove a properly torqued cummins head bolt that has not been subject to fatigue then it should retain its original length, (no stretch after load is removed)


Also I found a photo of what a stretch gauge looks like, this makes it easy to know if your bolts are ok to reuse or not.

93-12Smoke

When my head gasket blew my old bolts were about 1/16-1/8" longerthan the new Cummins bolts.

85crewcabbie

Thanks to all for the lively debate. When I picked up my replacement bolts at the cummins dealer in Tucson the cummins warranty rep from phoenix was there and I had a chance to talk to him because I wanted my new bolts under warranty. The rep was so polite and cheeky that I didn't even mind being called a dumbass in so many words. While he would not say anything specific about cummins bolt quality nor torque methods in general, he made it clear that cummins bolts are only strong enough for their method of torqueing. He hinted with a wink and a wry smile that cummins views head gaskets as a maintenance item. Use their bolts and their method and it will be fine for some time, but from the day you do the service the bolts are fatiguing and the gasket will start leaking and eventually fail even if you never overheat it or due anything to induce stress on it. It was quite the eye opening conversation straight from the horses mouth. In addition when I asked about retorquing used bolts he said with that same wink and wry smile that it's a waste of time because if your gasket needs retorquing your bolts are already failing and retorqueing them will more than likely lead to breakage. What I took from the conversation was I'm a complete dufus with respect to my expectations. My expectation that a head gasket with new cummins bolts will last until I induce a failure by overheating or other incident is just plain wrong said the rep with his wink and a nudge. Their bolts/gasket are actually of the barest, minimum quality as a system and have a limited life span under the best of circumstances. Again, not that he would specifically state this, but made it perfectly clear. So from now on I'll only use the ARP stud kit with the incremental torque method. And as I posted earlier If someone wants me to do a head gasket on their engine with only cummins parts I will use only the cummins torque method and offer no guarantee on my work against failure other than 30 feet or 30 seconds, which ever comes first. In stating what I'm going to do I'm not insinuating that I'm right nor making recommendations to any of you just as the cummins rep would not make any specific statements to me other than innuendo and wink wink and nudge nudge. If your having success with your method use it, you are neither right nor wrong. I do not have the intelligence to say one method or combination of parts are better or worse than another. But now that I've adjusted my expectations to accept that head bolts and gasket systems from cummins are not designed to live a long life (not that some don't - apparently by accident rather than design per the rep's cheeky responses) the next leak or blow out won't bother me nearly as much as I'm expecting it, it's inevitable.

taterfarm

Im glad you said debate and not argue, I hope that Im not causing problems just think there may be some confusion here somewhere.

I dont think I'd bet on what a Cummins warranty rep has to say especially when you approach with a claim on broken parts, I believe its his job and best interest to make all failures sound like a normal occurance that has happened by design and not by failure. I think he spends his days denying engine failures that cost many thousands of dollars to fix under warranty and that a mere $100 bolt set is an easy sell for him to send you on down the road thanking him for telling you that you have no clue. That wink, nudge and sly remark is why he does the job he does, makes you feel good that he pulled one over on you. I would feel much better if that information came from a casual conversation with the mechanic or an engineer that has no pay on the line for an honest conversation. I've talked with a few service managers and have little faith in their view when your there with a problem that will cost them money and every one of them has that same twinkle in their eye and say their your bestest friend ever and would never tell you wrong.


Do you have access to a place that can check the calibration on your torque wrench again? Just as a precaution I think it would be good to know for sure that there isn't a problem there. Regardless of torque method, type of bolt, cleanliness of the threads, or if the bolt should be reused or not, a new bolt should not have yielded like that at the torque you where at, that was only 110 ft lbs right?






Can you share some details on the history and procedure on those bolts?
where they ever retorqued
How old where they in years and miles
what was the max boost pressure you run
any other modifications

taterfarm

found this handy little procedure on doing a head gasket replacement, it shows what is acceptable when reusing head bolts along with what is not acceptable with bolts and the the head, it also explains the use of the stretch gauge.

Thought it may be useful and the best part about it is that it is from the cummins website and is an updated service procedure, not certain if its the most recent but believe it follow the factory service manual procedure that is disused in other threads on here

http://www.sbmar.com/Maintenance/PDF...orque-Data.pdf

patdaly

I have to take issue with this. We do not have the specifics of the composition or the post treat of these bolts. What we do have is the recommendation that the short ones get a 66 Lb/Ft. torque than a 90 degree turn. Does that take it above 110 Lb/Ft? I don't know, but I doubt it.

Not trying to argue, just point to what Cummins has specified.

taterfarm

We could have the specifics on the bolts, they were new OEM bolts and will have a detailed specification.

from past discussions on this site it has been said that they will exceed that amount on the final turn while following the recommended procedure, it has been said that they are around 125 ft-lbs at the end of that 90* turn.

I know this isnt an reliable source but in the re torque article in diesel power magazine they say the bolts should yield at around 151 ft-lbs but they do not state much for details on where that number came from or who gave the information. in that article and with many folks here they torque and retorque all the bolts to 120-125 ft-lbs. Again were back at the calibration of their wrenches on these values but ive read here many times where folks torque both new and used bolts well beyond 110 ft-lbs.

taterfarm

Any ideas on where we can find the actual rated minimum yield strength or minimum tensile strength for the OEM bolts? or who makes those bolts? Ive been looking all over and cant find much for info.

Ive been playing around with torque calculations and looking at friction k factors with different lubricants and see some huge variations in the torque it takes to reach the minimum yield strength for a class 12.9 bolt. just changing from oil to anti-sieze is around a 40 ft-lb variation in torque. then if you use some of those special torquing lubricants the change is more than double, its kinda scary to think about especially after reading a bunch of threads on guys torquing up to 130 and as much as 150 ft-lbs on a stock bolts. Makes me wonder what the OEM bolts are actually rated for and what these folks are seeing for stress.

patdaly

I doubt Cummins would release the drawing giving material and post forming treatment specs.

And yea, variation in oiling and even simple things such as surface finish on threads make a huge impact. It is one reason for the 2 step torque process, at lower torque values, the error isn't as much, and then above X torque, the turn method becomes the preferred method to assure values.