[noahp]

The fact that you heard it when the motor wasn't warm was part of my suspicion, as piston damage may be more audible while the engine is still cold.

Both due to the thicker oil mentioned above, and the fact that heat-generated expansion can reduce piston noise.

But I'm only making a suggestion. Don't go pulling your engine down..

Hey Pat great info sir. Is there a non invasive way to check for piston damage?

 

[noahp]

i could understand that if id been riding the bike for a while but i noticed it during a cold start

at start up the oil is tons thicker some where to the order of 10:1 or 20:1 and wont be thinned out and freely distributing until you warm up.

does this persists after it warms?

 

[noahp]

what's the oil fill look like? What grade of oil is in there and how were the local air temps when you started it? Also, how old and how many miles since the oil change.

I do't know much about the exhaust system but could see how the drop in back pressure might change things.