When you further tighten a bolt or nut that is already tight, like a
head nut, there are two things that take place. First, the nut has to
start to move -- and oftentimes this takes more torque than what
you're going to apply for tightness. This is called 'breakaway
torque". Second, you want to apply the torque required to keep the
parts together.
So...it's safest to back off the nuts a little bit and then
re-torque. Don't back it off with the click-type torque wrench,
though, as this reduces the accuracy of your torque wrench. It is
also most accurate to do this one nut at a time rather than loosening
them all. It is also possible to re-torque without backing off the
nut, if you're sure that the nut actually rotates before coming to
the full torque you want.
I also find that the valves need to be re-set after the head is re-torqued.
I also find that this can all be done after the engine has been
started and shut off several times, giving it several heat cycles,
rather than waiting until the end of the full break-in period. This
reduces the possibility of the gasket developing a leak during break-in.
At 07:36 AM 11/29/2005, John Mitchell wrote:
> What is the procedure for re-tightening the head bolts after
> break in.. Do I back off on the nuts first? Thanks John Mitchell 76 TR6
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