Yanmar 2GM20F Knocking sounds

[Lepke]

If no solution is found, a plugged injector can sound like a rod knock. Most injectors have a spring loaded valve near the bottom that closes off the injector from combustion debris. It can have a weak spring or become stuck. It can be intermittent.

[sveinung]

New mounts ordered, I'll report back! Appreciate all the responses.

[sveinung]

Reporting back:
New mounts in, surprisingly straight forward after I picked apart the cockpit, threw out the water heater to get access.

Redid the mounts, as best as I could with feelers and think I didn't mess it up too bad. Knocking is much better, but I can still find an RPM (just over idle, in gear, forward) where I can hear it.

The mounts although new (40 and 50 shore as recommended) seem pretty soft so it's still rocking around a bit. I read elsewhere that the combination of soft mounts and soft coupler (that 1inch rubbery disc) is not ideal since you now have 3 flex points along the boats axis.
Since mounts are new, i have these questions:
1. Should I get a solid insert (would need something that builds about the same 1" thickness so I don't move prop)?
2. Would the coupler get softer over time so it's due for replacement?
3. Any other good ideas? Harder mounts?

[Lemsteraak]

I had a similar problem with my 3GM with the mounts bottoming out. Make sure you have the right mounts in the right places. Mine were installed wrong with the softer mounts at the front of the engine. My knocking was when I let up on the throttle and sometimes at idle and was really loud (steel hull), The secret to longevity of these little engines seems to be clean fuel, clean air and clean engine oil and change transmission oil. If the knocking sounds internal, you can always try listening through a big screwdriver. Put the sharp end on the engine and put your ear to the other end and it is like a stethoscope to help locate the sound.

[chasfgr]

My boat came with the 2GM, that always knocked and writhed around, except at about 1850r pm.
Fortunately that engine expired (rebuild was more expensive than replacement).
I replaced it with a 3YM, ostensibly the same power but 20% more in practice and a far more usable power curve. That only knocks when I have the tickover too slow.
So - I fear it's the nature of the beast, 2 GMs are just noisy workboat engines.
A bulk purchase of earplugs may be the most economic answer to the problem.
Having a self-pitching prop made it all very simple on changeover.