I have an old 350 chev motor likely 1980 and it's in a boat..the milage is unknown the compression is between 135 - 145. just put a new double roller chain and gear on,I had to use a new chrome cover all they had..it had a nylon gear single chain in it wore out...now when running it has a tiny tick/whooshing sound that's on and off,it will make the sound for 2 sec and stop for 2sec on and off..when you rev the motor it doesn't get worse or louder but doesn't go away either, obviously rev the motor up more you can't hear the sound because of the motor rev up but it's still there..the motor it self sounds great...I think it's the stupid chrome cover but Idk...took the cover back off but it had no marks on the inside...I checked the water pump bearing its not that....Anyone ever run into this