low rpm knock, need advise

[87blf125]

i have a 1988 force 125, it has just started knocking at idol and lower rpm. when the boat is getting on plain and when i am at wot motor sounds fine. it starts and runs fine. it does seem to make some noise when power loading the boat on the trailer.
this noise has just started happening the last 2 times out with the boat. i checked the compression and it is 130 on all 4. i also pulled the plugs and put a screw driver in each cyl and turned the flywheel by had back and forth to see if it i could notice any slop in the pistons and nothing. i am thinking bearings but thought i would see if anyone had any other ideas before i decide to rip into it or sell it.

 

[DukeDelago]

Re: low rpm knock, need advise

I'm sure some of the other guys on the forum can give you a better idea of what's going on, but I had a similar issue and will share my experience and hope that it helps somehow! I have a 1990 force l-drive that had a knocking at low rpm when I bought it. It was not noticeable at anything but idle speed, but at that range could be heard easily. To this day I can't tell you what was actually knocking, but the boat ran for two years and hundreds of hours without any issues. Eventually the motor did blow. I needed all new pistons and rings, one of the pistons came apart pretty good, the others were not much better. Anyway, once I rebuilt with new parts (and a crankshaft bearing on #1 that I wasn't expecting, $120 for half an ounce of steel!) the motor started up after the rebuild and ran just the same as it did before, only no more knocking. Hope this helps in some way!