2008 Mercury 15hp outboard (F15M)

by Mike
(Toronto)

Hi, Hoping you folks can help me out.I have a 2008 15hp Mercury outboard (F15M) that started making a knocking noise.Here is what I’m observing
- no problems starting (pull rope)
- forward/reverse gears both engage
- in neutral, faint knocking sound at regular interval
- when in fwd/rev gear low rpm, vibrating more than in the past
- knocking cadence increases with higher rpm, but eventually fades at full throttle and engine rooms smooth.
- when returning to low rpm in fwd gear, lots of vibration
- when turning engine off while in fwd gear, with the run/stop toggle switch, engine cuts then knocking gradually slows down down (engine off & impeller not spinning at soon as I toggle the switch)
- this knocking is very clear sounding and it seems to be coming from just below the engine but hard to say
- when turning engine off with button at end of tiller, the above doesn’t happen, engine turns off and there is no more knocking at all
- putting gear in reverse sometimes makes a grinding noise.

That pretty accurately describes what’s happening. Wondering what you all think?

Thanks
Mike