Hi Jon,
I just read your comments on the AD about piston and liner ovality.
One thing.. when you get in there, try to measure the roundness and
taper of the cylinders and pistons if you can.. I am told that they tend
to wear oval, and if that's the case (beyond a small amount) you should
just get new pistons/liners. Same if there is too much ridge at the
top, that won't hone out.. can cause those rings to go sooner than they
would have.
You might like to know that pistons are made oval, yes that's right they are
manufacturered to be oval in shape and tapered from top to bottom. The crown of the piston
is a little smaller than the bottom as it heats up more on the crown than the bottom
(skirt). Consequently when the piston is at operating temperature it grows to fit the
liner, before that you often hear "piston-slap" on a new engine as the clearance is too
large with a cold engine.
In fact the ovality can be quite big. The reason is that when the piston heats up in
operation the piston grows in size and fits the bore better. If you don't believe me go
and look at a piston manufacturers website to get the details. It isn't a lot but enough
to be measurable on a new piston.
Moral of the story? Hone those bores at your own risk!
John
Durban
South Africa
Alfetta 1.8L turbo
Yep, I was aware of the piston "ovality".. the pistons expand
differently, due to a lot of metal thru the piston pin axis, and not as
much 90 deg opposed.. as well as that taper. I should have mentioned
that. The ovality (hmmm is this a word?) is designed so that when the
engine is hot, the piston ends up more or less round.