Brian is right. TTY bolts are *designed* to stretch. They're often used in
cylinder head application as the plasticity is a designed part of the
clamping force. Often employed as a cost cutting move by most every
automaker these bolts have to give a little but still retain their clamping
force during extreme heat cycles. The demands are even greater on engines
where the block is iron and the head is aluminum. The clamping force isn't
"constant", but within "spec".
5 re-uses is remarkable. Most TTY bolts I run across are USE ONCE.
But, Peugeot also specifies head bolt retorques - which is also something
I've only seen with Peugeots.
When I do my N9T, I will use studs and no retorque.
However, the factory spec should be fine. The big killer of head gaskets is
nearly always a compromised cooling system. On iron block/aluminum head
cars you get no second chance. Why hose makers (Dayco, Goodyear, etc.)
don't use this compelling argument in sales literature for changing out your
cooling hoses on a scheduled basis, I don't know. The way I see it, cooling
hoses are as important as timing belts (if you got one).
K o l l
- Original Message -----
From: "Brian Holm" <peugeots@vtlink.net>
To: "con" <phred@exemail.com.au>; <peugeot-L@yahoogroups.com>
Sent: Tuesday, April 18, 2006 7:53 AM
Subject: 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.
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Received on Tue Apr 18 14:12:30 2006
