wondering if anyone else has seen this. at idle engine is smooth no noise. If you are driving there is no noise, however as soon as you release the throttle the engine makes several knocking sounds then returns to smooth idle. this can be reproduced under load and under no load. If the throttle is feathered at about 1500 rpm the knock is consistant. But above 1500 the noise is gone. My stethoscope makes me believe its low in the engine but hard to say. The engine was in a previous roll over so dunno if that has anything to do with it. What do you think valves need adjusting or .... bearings?

 

This does sound to me like a rod-related knock, maybe little-end. Main throw rod knocks don't usually come and go with RPM's- they usually just knock, following the RPM's; but the piston end is more sensitive to changes in engine load and can come and go and can respond to changes in oil pressure.

But before I get derailed- would you describe the knock as having a regular 'period', like "knock, knock, knock, knock", basically matching RPM's, or more like a double knock- "knock knock, knock knock, knock knock, knock knock"?
Hard to describe with typing....

 

after throttle is released there are 3 to 4 knocks that seem to be in tune with the rpm decreasing. Don't think I would call it double knocking just one solid knock followed by 2 to 3 more that are progressively less noisy and spaced out until it gets back to idle which is then quite. The only rod knocks I have ever heard are consistant with rpm no matter at idle and never have a period of quite which made me think maybe something in the valvetrain. Hopefully I can get a video up for all to see.

 

Well just in case anyone else in the future has this problem this is what I found. I'm not sure which came first but I found #2 cylinder wrist pin pretty rough to move around not really bad but not as smooth as the other cylinders. I also found that this caused a fair amount of piston slap on the cylinder wall. The one thing that is a little wierd is that #1 main bearing was pretty screwed up almost looked like it got pounded on. Dunno how long the engine was running when it was upside down but maybe the pickup was out of the oil for too long. Doesn't look like anything a good machine shop can't fix.