Mercury 2.5hp 2 stroke, possibly about 2011

by Keith
(Auckland, New Zealand)

Starts and runs fine but has a knocking noise. Noise will sometime go away, but seems present at all RPM's

I have:

Had the gear case off, changed oil and inspected gear teeth. Checked the bearings

Had leg off and checked drive shaft.

Had the power head off and checked bearing play.

Some history. I bought two of these from an auction site. Found out later that one of them had been dropped in the sea and absolutely nothing done about it so that one is sized solid. But the other one is in excellent costmetic condition and starts / runs reliably.

The knocking apund is the only issue, it just doesn't sound right. I have found a few YouTube videos of these motors and I don't really detect knocking when listening to them, so I don't think it's normal.