Thread: ARP head studs

Originally Posted by The Mutt

...tightening in the reverse order to Ben's pic, I'll tighten from centre out assuming a 1982 motor should be treated the same as a 1987 model and newer.

Glenn

In general (not just for heads), the tightening pattern should start from the stiffest part and extend toward parts of lesser stiffness.

99.999% of the time this will be from centre out to furthest ends.

If the end bolts are pulled down 1st, their clamping force combined with friction will restrain the centre ever so slightly and increase its stiffness, enough that it is highly likely that the bolts near the centre will not be able to develop the same clamping force on the gasket.

Looking at the second last post on the first page if you need to final tension to a degree angle then they are probably TTY (torque to yield) and so should be replaced every change.

One IMPORTANT thing with ARP, run at least 3 pref 5 torque sequences to stretch them. They don't distort but it is the recommended preparation. Also use moly gease as the lube not oil it won't hold under the pressures created. The ARP lube (read expensive) is just this anyway.

And also check the tensions after torquing as as stated earlier the inners could be looser post full tension. Don't loosen just test again with tension wrench.

When torquing up main caps and big ends on large caterpillar engines they are done to a setting,then angle turned an extra so many degrees.They don't require the bolts to be replaced everytime so I'm wondering why you would on an isuzu?
Cheers Eric

A lot of people assume that bolts tightened by a angle of turn method are reaching yield, but it is not necessarily true.

I haven't conducted any tests to see one way or the other what is happening with the Isuzu head bolts. It depends on more factors than thread pitch and tightening angle - for example while the bolt is stretching under tension, the head is compressing and how much depends upon the height through the head and thickness/distribution of material around the bolt hole.

A reasonable test would be to accurately measure the bolt length before and after it has been in use to determine if permanent stretch has occurred. Cummins supply gauges for checking some of their bolts and they allow them to be re-used unless the permanent stretch makes the bolt length exceed the gauge length.

Edit: I had a careful look through the cylinder head section of my manual, and they give a host of measurements/inspection instruction for many of the components, but no mention of head bolts with regard to inspection or discard/replacement.