Cat 28 MKII Damper Plate

[Alec]

My M25XPA vibrates badly at idle, in or out of gear. I've replaced the engine mounts & injectors and had the marina tech verify that my idle is set to 1000 RPM using a digital tach, all to no avail. Someone mentioned that I should check the Damper Plate, so, having nothing better to do on a cold January day I decided to pull the tranny and have a look to see if there was an obvious problem. Aside from a little bit of wear on the splines I don't see anything amiss.
Does anyone have any advice as to what to look for in a damper plate?

 

[Tom J]

rough idle

Don't know anything about the damper plate, but I had the same problem with my M25. When I bought the boat, the idle was set at 1200 rpm, and the surveyor said that was too high, should be at 900 to 1000 rpm. I went ahead and adjusted the idle to 900 rpm, but the engine shook so much in gear, that the clamps for the heat exchanger broke, and I almost lost the exchanger to chafe damage. Turns out that the recommended idle for the M25 is 1200-1250 rpm. Very little vibration at that speed. I set the idle at 1250 rpm in neutral, and it holds at 1200 in gear. I think that because the engine is a 3 cylinder, there are optimum rpms where the dynamic imbalances cancel each other out. You'll find that throughout the rpm range, there are places where the engine runs rough, but at others it is very smooth. At cruise, 2500 rpm, she's smooth as silk.
Good luck!

 

[Alec]

Re: rough idle

Thanks for the reply, Tom. It sounds as though your experience is exactly like mine. The thing that troubles me though is that my slip neighbor has a Catalina 30 with an M25 & it is as smooth as silk. Same block as ours. The only real diference I see is the motor mounts, which are the older style. I considered using that type when I replaced mine but was advised against it by my marina folks.

 

[Banooma]

Hi Alec,

I don't know if this might be the same issue, but here are my two cents... my 99 mkII had a loud vibration that was coming from the bell housing clanging against the fiberglass. He adjusted by slightly raising the engine on its mounts. Sorry I have no damper plate advice!

See you out on the bay!