Golden Jubilee
Posts: 5187
Joined: Thu Nov 29, 2012 9:28 pm
Location: Lyman, IA
Re: Need Help Diagnosing Engine Knock
If I had to guess I would be looking at piston slap, esp because it goes away when the cyl is unloaded. I'd still check the valve clearance and cam lift with a dial indicator before I pulled the head and popped the piston out. Piston clearance can be checked with the rings removed either with an inside mic on the bore and an outside mic on the piston or with special long feeler gauges for the job. A loose fitting piston pin should be able to be felt by hand with the piston and rod removed, and held in your hand. The fitment of the pin can be checked with an outside mic and a "T gauge" in the piston.
Pistons can b knurled if it is a loose fit in the bore and the clearance isn't so great as to require an over bore.