350 chevy vibration

[slickone]

I'm new here and would like some help with my 350 chevy motor which is in my boat. The problem started last fall when I loaned my boat to my son. When he returned it the pulley that drives the power steering and alternator was cracked.

He bought two pulleys at an auto parts store which fit together and work but they were not the stock pulley.

I changed the oil last fall as well. I took the boat out last Sunday for the first time. It starts and idles fine but when I raise the rpms the motor seems to start knocking or vibrating. I noticed it runs a lot hotter than before I loaned it to my son.

I checked the oil and it's clean. I checked the compression and it's 155 high and 142 low and pretty even in between.

What could possibly be causing this problem, and how do I isolate it?

S1