Originally Posted by piniongear
Thanks for the quick reply.
I thought to check the flywheel carefully for cracks, but it looks good.
My description of it knocking when it gets ready to shift may have been a little misleading. When I sit there in neutral and bring the rpm up to about 2500 the knock begins. And it sounds like a rod knocking too.
Maybe when I get the rods off the crank I will see some kind of damage. This is not my first time to work on a Chevy, but it is the most serious problem I have encountered.
In other words, I am in deeper than ever before and I still don't have the pistons out yet.
Rod knock is the typical double knock. But pin knock and piston knocks are also double knocks they differ from rod knocks in tone but not frequency.
Piston pin knock like rod knock happens as the piston and rod assembly change direction and the slack of excessive clearance is taken up. Piston knock is typically from a cracked skirt which flexes every time the piston changes direction and the skirt snaps across the bore clearance between its thrust and non-thrust sides.
It's often hard to tell the difference between these unless you've heard them a lot.