Which bolts can only be torqued/used once.

[ward00]

My understanding is flywheel bolts can only be torqued once - is there a reason?

What other bolts should only be torqued once, head, rod .... ?

[18Fiatsandcounting]

I think what you are referring to is "Torque-to-Yield" (TTY) bolts, which are designed to stretch along their axis in such a fashion as to provide optimal clamping force, especially between different metal parts (iron block and aluminum cylinder for example) and with less clamping variations occurring as a function of temperature. They have come very much in fashion in 21st century cars and are used in applications such as cylinder head bolts, crankshaft main bearing cap bolts, flywheel bolts, connecting rod bolts, etc.

And you are right, TTY bolts should NOT be reused as they have already been stretched close to the yield point in their stress-strain relationship, and reuse could result in broken bolts, insufficient clamping force, etc.

I have never heard that Fiats of the era we're talking about ever used TTY bolts, but that's not proof that they didn't. So, if you can determine that the bolts are TTY, do not reuse them. If they are regular bolts, you can reuse them (within reason, of course).

In either case, clean and lubricate the threads before torquing. A lot of the torque that you are applying when torquing a bolt is going into friction between the head and where it contacts, and between the threads, and this torque isn't going into clamping force (which is really what you want).

-Bryan

[ward00]

How does one identify tty bolts?

[18Fiatsandcounting]

I'm not aware of a way to identify TTY bolts by looking at them, but if the Fiat shop manual for the car specifies that the flywheel bolts are to be used only once, or the tightening torques are specified in terms of angle (degrees) rather than ft-lbs, those are pretty good indications that you are dealing with TTY bolts.

If your Fiat flywheel bolts are original, I'd be surprised if they are TTY. If they are not original, they could be either, but it would be kinda unusual for a previous owner to switch to TTY bolts. To play it absolutely safe, you probably should just get new bolts and then you know.

I have to say that, in all the 1960s through 1980s cars that I have owned or worked on, I've never run across a TTY bolt. With the caveat that I have never worked on a diesel or high performance engine.

-Bryan

[ward00]

I might be confusing the Fiat flywheel bolts with another car I had, but at least one of them specified not using flywheel bolts over. I'll defer to those here that know what the FIAT shop manual says. As for my Carrillo rods, I found out they do use bolts that can be reused only a couple times.

[Odoyle]

From what I recall has been said in other discussions on this topic, headbolts through 83 could be brought to torque around 15-20 times before showing fatigue, and it could be said that this would be similar to most other fasteners on the car, including flywheel bolts.

[ward00]

Just found some info on the RIBE type head bolts that some of the vendors are selling and are intended for use with Astadur head gaskets. The Guy Croft site indicates that the RIBE bolts should not be reused more than a couple of times. Since I intend to uses a Astadur head gasket, this was good info to know.

[fiatfactory]

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[SteinOnkel]

The way I determine if something is TTY is by looking at the instructions (factory manual, fastener manufacturer usually provide them as well). If it goes something like this:

1. Torque to 30nm
2. Torque to 90nm
3. Rotate clock-wise 90 Degrees

Then they are tty.