Lots of questions going on about Head Bolts. Here's how I deal with them
(never had a head gasket fail)
First, when you torque a bolt, although you are measuring the resistance to
the bolts turning, this is not to determine how tight the bolt is, but
rather how much stretch it has. Head bolts are actually stretched and thats
what holds the head on. It's just impossible to measure otherwise. Race
engine manufactures will measure the length of a bolt on a connecting rod
(because they can), knowing how mutch stretch they need.
Before installing the head, run a tap into the threaded holes in the block,
and make sure you clean out any debris.
Inspect the bolts for damaged threads, pitting, rust etc. If there is any
damage, toss them unless you absolutely have to use them again. They will
stretch differently if rust or pitting is present. Older head bolts are
torqued and when removed basically will return to the original length. You
could measure this length if you can find the original specs. Newer
vehicles tend to use head bolts that are "Torque to yield" These bolts have
to be replaced, as they permanently deform when torqued. Our old stuff, we
don't have to worry.
When you install the bolts, ALWAYS oil the bolt threads (just coated, not
dripping) if the threaded hole in the block is a blind hole. If the head
goes into the water jacket or joins an oil gallery, use silicone.
USING STUDS. When using bolts, the bolt actually will twist like a torsion
bar. Friction in the hole in the block can also help give a false torque
reading because of the resistance (hence the oil, or uncured silicone acting
as a lubricant). Once you remove the torque wrench, the bolt will naturally
try to "unwind" itself. Tightening a nut on a stud creates a straight pull
on the stud, and not a torsional twist (which is what a torque wrench is
also measuring). Straight pull equals more precise torque readings.
THE RIGHT WAY TO PUT ON WASHERS. If the head bolt has a washer, look at the
washer to see which way it was stamped. One side will be minutely convex,
the other concave. The convex side ALWAYS goes towards the head of the
bolt. Looking at the concave side, around the hole, you will notice the
edge is slightly sharper than the convex side, from the stamping process.
This sharper edge could in theory nick the bolt where the head meets the
shank. Yes, this correct way to install washers should always be followed,
not just with head bolts.
When I torque heads, cranks, rods etc, I follow the manufactures pattern and
steps first. Then I repeat the pattern at the final torque setting twice.
If even one bolt or nut turns, repeat, until you sucessfully go around twice
and nothing moves.
Sounds like a lot of work, but believe me it only takes one or two extra
times. Any more, then something isn't seated, or the bolts are toast.
I worked as a mechanic for the local Phone company (fleet of about 900
vehicles), and we could not afford the down time to bring vehicles to
retorque the heads after an overhaul. Like I said, I never lost a head
gasket! My personal vehicle I can afford the time, but only retorque bolts
that were lubricated with oil, and leave the siliconed ones alone.
Sorry I got so long winded. Hope this helps.
Bob Winslade
1966-1600
1967-1600
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