Started knocking when it heats up now. Still hasn't lost compression but we are pretty sure a piston has started to collapse or a gudgen pin is screwed.

Going to rebuild the bottom end in a few weeks time.

it is not the pistons my old nissan n10 a14 eng don the same thing it is the crank shaft is bent have a look at the oil let oll the oil out of the eng u will see bits of coper

Maybe spun a big end.

Craig

maybe the piston rings are broken?

I had an a15 with the same symptoms. While it is making the knockoing sound, pull of or short the plug wires one at a time. this will tell you which cylender is at fault. If depriving the spark makes the noise stop, then it is the piston (as when threre is no spark there is no load on the offending slug). My A15 had a broken ring land on #4. I never did find the missing bit of piston though.

Quote:And of course, when you take the load off the piston, you also take the load off the bearing. This is a standard test for isolating which cylinder is in trouble. A compression test will help to identify it if the piston, or rings are at fault.

In the end, you gotta pull the engine out & dismantle it, so bite the bullet & take it out before the damage gets worse.

Do a compression test, I have had trouble with valve seats "falling out" when warm. When cold they usually stick in. Maybe it is a sign, maybe with forced induction it would hold the seat in place ;)