RE: [Peugeot-L] TTY bolts, was: 505 Diesel radiators & heater core by-pass

Con,

I assume that the metallurgy is different in the TTY bolts, allowing more elasticity. I haven't tried it, but someone might try the TTY procedure on a standard bolt and see if it is longer when you take it back out. I'll bet it is, if it is still in one piece.

As I get it, the principle behind TTY is that there is a zone of elasticity where the clamping force is constant throughout the expansion cycle of the head during engine operation.

On Peugeot's recommendation, I have no idea why the number of reuses is the criterion, unless totally relieving the strain on the bolts by taking them out has some cumulative aging effect on them.

I don't think there is much chance of encountering TTY bolts used more than five times if they haven't been switched from engine to engine, because the head gaskets tend to stay put when you use TTY bolts, in distinct contrast to the earlier bolts.

Brian
At 09:04 PM 4/17/2006, con wrote:

>Brian,
>
>Thanks for your interesting comments.
>If Peugeot's tightening toques do not force the bolts into the "plastic"
>region (that is, they remain elastic and return to their original length)
>then any bolts, cheaper ones than TTY can be used. Which begs the question
>why spend the exorbitant money on TTY ones?
>
>Peugeot's reuse recommendation is also interesting: I guess the question is
>"how do you know if the bolts have been re-used once or five times".
>At the end of the day, as you say, they should be measured before reuse:
>Obviously, the undeformed (original) length would need to be known.
>
>
>
>Con....
>
>1979 504 GL
>1984 505 STi
>1998 406 SV
>
>
>-----Original Message-----
>From: Brian Holm [mailto:peugeots@vtlink.net]
>Sent: Tuesday, April 18, 2006 2:24 AM
>To: con; peugeot-L@yahoogroups.com
>Subject: RE: [Peugeot-L] TTY bolts, was: 505 Diesel radiators & heater core
>by-pass
>
>Con
>
>Peugeot says you can reuse the TTY bolts up to five times. The
>recommended tightening procedure should not deform the bolts
>plastically. They should return to their normal length upon
>removal. Of course they should be checked to be sure, and any that
>are too long discarded. They are now obscenely expensive if bought
>separately from Peugeot, not so bad if bought as a set with the head gasket.
>
>Brian Holm
>
>At 07:43 AM 4/17/2006, con wrote:
>
> >I'll try to remember basic metallurgy.
> >
> >"Torque to yield" bolts (if torqued to specification) cannot be reused
> >because they have been stretched beyond their "elastic" region, into what's
> >called "plastic" region: Elastic means that they return to their original
> >length. Once stretched into the "plastic" region they stay elongated and
> >hence new bolts are required.
> >
> >Con,,,,
> >

Brian Holm, Parts for Peugeots
at Peugeot Holm, since 1969
2120 Maple Hill
Plainfield, VT, 05667
802-454-7132, fax -1310

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