Are pressure plate bolts "one time use"?

[JohnK]

OK, here's today's dumb question...

Are the Ford pressure plate bolts (M-6397-B46) for the Coyote "one time use" bolts?

More specifically, I had installed the flywheel onto the engine a while back, and then installed the clutch and pressure plate and torqued the pressure plate bolts down. I temporarily set the bellhousing on the engine, and then set the engine aside as I worked on other parts of the build for a bit. I went back today to continue engine/clutch/trans assembly and it dawned on me that I never dial-indicated the bellhousing before bolting on the pressure plate. So, the pressure plate's got to come off now. However, these bolts are "torque to yield" so I'm assuming that even though I never ran the engine since I torqued the bolts I now have to replace them? Is that correct?

Thanks,
John

[edwardb]

You'll get different opinions. Whether they're TTY or not, they do have a factory applied thread locker. They're not expensive and not a place easy to reach or where you want a failure. For $20, I say start new.

[NAZ]

Replace them. Expensive? Not nearly as much as the results of a failure. In aviation we had a saying: If there is any doubt whether to replace something -- there is no doubt.

After working with Fastenall engineers I have come to realize that any critical fastener should be replaced after it's been torqued (yes I know some OEM provided fasteners are claimed to be reusable a finite number of times). The first two threads hold most of the load when a fastener is torqued and can be stretched to their yield point. Even if they do not deform the surfaces become distorted and galled so that the next time you torque them it takes more torque to properly stretch them. And unless you measure the stretch while applying torque there is no practical way to determine how much more torque it takes. Torquing fasteners is a practical way to achieve the proper bolt stretch and is based off the torque / tension relationship of new threads. So saving so $$ on fasteners seems like a good thing until you experience a failure. I've seen lots of failures and working in an industry where failures can be devastating has made me especially hesitant to reuse critical fasteners.

[JohnK]

Thank you both for talking me off the ledge. I was mad at myself for a silly mistake and impatient to move forward so was hoping someone would say it was OK to re-use them but deep down I was pretty sure that this was the right answer. Also, had I bothered to go back and re-read the instruction sheet for the bolts I would have seen, in large bold print, the following:

NOTE: The bolts are one time use torque to yield. Do not reuse bolts.

So, new bolts are on order. Off to do other stuff in the meantime.

Thanks,
John

[SSNK4US]

There are never any dumb questions John. If you don’t ask you don’t learn right? Sure there are lots of non critical nuts and bolts that can be re-torqued. Lug nuts would be a good example, they all have a torque spec and they are reused many many times. But any bolt that has an “angle” torque should never be reused.
Just some extra 2¢

Kurt

[GoDadGo]

In aviation we had a saying: If there is any doubt whether to replace something -- there is no doubt.

Best Quote I've Seen In A Long Time!