Boat ran fine at Big River all weekend until the end of the day. It started knocking hard, then we killed it. Floated to a random house and picked it up with the trailer. I'm trying to figure what caused the knocking because we started it quickly after that and the knocking went away. We only had it idled for about 15 sec but no knocking. The boat has 60 lbs oil pressure, oil is clean ( no flakes or chunks), pulled the valve covers off and turned the motor all the rocker arms were going up and down properly. It did not overheat. Did a compression check (note that the gauge is does not go to 0 but stays at 20 psi, so maybe +20 to my numbers)
My only guess is one of the lifters went out to cause the knocking and then somehow started working again. The variance in the compression, because 5 and 7 are next to each other, may be from a leaking head gasket?
My buddy is suggesting to pull the heads, get them milled down, and checked out. Get a new cam and lifter while I'm at it. Easy for him to say because he's not the one paying the bill. The guy at the machine shop said if the noise went away it is most likely top end.
I almost wish I found something broken. Now everything seems fine, but I do not want to chance it.
Its a BBC 454 with 049 heads.
Any hints on further diagnostics?