I'll first admit I dont' know that much about these new head gaskets that
require no re-torqueing. I'll ask my broghter - a mechanic, and let you know.
From a purely engineering aspect, though, I can tell you that - as Grame
Sucking says, on older technology gasket, that you must retorque them. It's
not a question of a the head gasket alone, per se, it's a question of the bolts
elongating over a period of repeated heating and cooling. If the head gasket
AND bolts can absorb the expansion between the block and head - great
(obviously newer technology and having more to do when the gasket than the
bolts). That being said, if either the bolts or gasket can expand and contract
during repeated heating and cooling of that joint, then you're going to
eventually get leaks. BTW, my brother always does from the inside out (and
side to side) so that the middle of the head doesn't bind as it would if you go
from the ouside in. That's like trying to spread out a blanket starting at the
ends
and working your way to the middle.
BTW, I can't think of a single reason to loosen the bolts first before you
retorque them (as long as you don't over-torque). You're just recreating the
problem you're trying to fix. Well, you are stressing the bolts, but that's
the point or torqueing in the first place. Remember, the reason for torqueing
in the first place is to provide just enough stress in tension for the bolt
threads to seat and not come loose (sliding friction).
My brother showed me a great experiment during the rebuild of my engine last
November. He let me "torque" a bolt (in a non-critial area) using a
single-pass (mono) torqueing technique. He then did it the proper way - torque
the bolt, let it expand/relax and re-torque it after it had had a chance to
relax(same, exact torque setting). It was VERY obvious why the latter
technique provide a much more secure bolt. The one I did on a single pass came
out pretty easily. The bolt he torqued using the proper techique was more
difficult (but of course, not impossible) to remove but with greater effort.
Good luck. Hopefully sombody on teh list has more insights in these new bolts,
head gaskets.
Regards,
Perry Smith
'68 2000
Do you Yahoo!?
Yahoo! Finance Tax Center - File online. File on time.
|