shouldn't torque-to-yield head bolts be re-used
Torque-to-yield (TTY) head bolts are designed to stretch
when used. Once stretched, they are not as strong as before.
Consequently, they cannot provide the same amount of
clamping force and may break or shear off if reused.
The TTY bolt-tightening procedure is designed to provide a
better, more uniform seal. On the factory assembly line,
sophisticated torquing equipment is used to tighten head
bolts beyond their yield point. This stretches the bolt
slightly and evens out the loading so each bolt provides
almost exactly the same amount of clamping force on the head
Because the tightening procedure permanently stretches the
bolts, there is a risk of breakage if reused. Since there is
no way to tell how many times such a bolt has been reused,
most aftermarket gasket manufacturers say the risks of
reusing TTY head bolts far outweigh replacement cost. For
that reason, new TTY head bolts are often included in head
Applications where new TTY head bolts are recommended
include Chrysler's 2.2L and 2.5L engines, Ford's 1.6L and
1.9L Escort engines, General Motor's 1.8L, 2.0L and 2.5L
fours, 3.0L V-6 and 381 diesel V-8.
When new TTY head bolts are installed, a special tightening
procedure must be used to achieve proper results. After
bolts have been tightened to the recommended torque, each
bolt must be given an additional twist. The amount of twist
may be 1/4 turn or more, or specified as so many degrees of
rotation. Using a simple "torque-to-angle indicator" tool
when making the final twist ensures uniform loading and
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