Good day all. I've opened my engine for the first time after 260 000 km. Had to replaced all rings and bearings after a suspected engine knock. Later I discovered that the second piston was slightly bent, so had to replace the second piston too. I put everything together cranked the engine and nothing. The engine turned a couple of times then wouldn't crank at all. Tried to manually turn the crank and it wouldn't turn however, it turns when I reverse the rotation with no effort.

So I reopened the entire engine and checked the rings, bearing, pistons, crank and valves and didn't see anything out of the ordinary.

I manually rotated the engine with the top off and crank turned with no issues.

So I put everything together again and the engine cranked more times than the first time. It would fire up for a second then switch off. Now the engine won't turn via starter or manually. But then again turns backwards then forward and stops again.

I've checked everything I could think off. Can anyone point me in the right direction as to what could be causing this issue?

Thank you in advance.