The extent of engine rebuild is determined by a couple of concerns:
What is worn to the point the it is reasonable to expect failure within
a reasonable time.
How much do you wish to spend
How long do you expect/wish to keep the vehicle
Do you plan on using it in situations of heavy loads or long trips
A number of considerations:
If pistons are removed:
o inspect the cylinders for wear. Smooth walls, with a few very
shallow scratches, will be OK. Look for gouges/long, straight scratches
up the walls. At the top of travel of the pistons, look for deep wear
where the compression rings reach the top of the cylinders. These will
determine whether the cylinders need boring. If OK you will need to
hone the walls to insure that the new rings seat OK. If the cylinders
are acceptable, then:
On the pistons themselves:
o inspect for damaged ring grooves. This is very important. Worn
grooves, even with new rings, will permit the new rings to wobble, and
ultimatly break.
o look for scoring on the walls. Unless very bad, this won't hurt
anything. Watch for "galling." This is where the pistons have been
overheated from lack of lubrication or low water. Such pistons should
not be reused.
o use a micrometer to determine wear. If too much, you will get
"piston slap." Won't hurt anything, but at low RPM's, you will hear it.
As to cam bearings, these, as a rule, rarely require replacement. Some
exceptions are where there has been damage such that metal flakes or
such material has gotten into the oil, and has been carried through the
engine. If a new cam is to be used, it would not hurt to replace the
bearings, but again, unless there is real damage requiring that the a
major rebuild is to take place, don't bother. Main concern with cams is
the end float. This is the motion from front to rear, and is a function
of the retaining sleeve.
Cheers.
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