Engine Vabration

[bobcat30]

I have a Universal MK25 diesel. I get a vibration when under power. I start the engine and I raise the RPMs slightly to get it to stop vibrating. I cruise at 2500
RPMs and it is fine (no shaking). If I go to 3000+ it starts again. I don't normally run that high.
I always have the shaft and prop checked each launching. The bearings on the shaft ware changed two seasons ago.
So, that said, any suggestions to stop the vibrations and shaking at low speed?
Thanks, BobCat

 

[Don S/V ILLusion]

have you inspected the engine mounts?

 

[foolproof]

Mine does the same thing with the Yanmar. When the engine idles the water around the boat looks like an ultra sonic cleaner ... tons of little waves radiating out from the boat. I suspect the motor mounts, so that is where I would start on yours.

 

[dj2210]

There are several things it could be.
1. The Cutlass bearing
2. the alignment of the cutlass bearing
3. Motor mounts
4. Engine to prop shaft alignment
5. Bent shaft
6. Unbalanced prop
I also have vibration. Not knowing the last time the cutlass bearing was replaced I will have that done. Also my motor mounts are coming loose from the stringers and will need fixing. I have also read that the mounts should be replaced after so many years and since mine are probably 22 years old that it is probably time.
Let us know what you find out.

 

[Stu Jackson]

So, that said, any suggestions to stop the vibrations and shaking at low speed?
Thanks, BobCat

Bob,

Yes: raise the minimum stop rpm, do just do it manually with the throttle. There are two screws on the forward, top, starboard part of the engine and one of them is the minimum stop.

Our M25 engines shake and rattle at various rpms. It's normal. All engine mounts will do is change the amount of vibration you feel in the hull and decks, it will NOT stop the natural vibrations of our M25 engines.

Adjust the throttle first, then see if there's anything else going on as suggested by others.

Also check the belt tension. Floppy alternators add to vibration.

Have you upgraded your alternator bracket?

 

[anchorclanker]

Simplest would be to remove the prop shaft flange bolts from behind the engine, and try running it in gear at those speeds. If there is no, or less vibration, your problem is either misalignment of engine to prop flange, or something downstream. Once the flange is disconnected you can check the alignment. Its its off, it might be a good time to install new mounts before you start aligning the engine.

 

[jimmcgee]

Bobcat test in and out of gear to isolate the vibration to the engine or drive system.

One way to determine if it's your mounts is to wedge a pry bar or boat hook under the mounts through the starboard access door. On my boat I could feel & hear a noticiable difference when I did this.

If you have the 25XP I'd recommend going with the Vetus K75 mounts rather than the stock Universal mounts. There's a good writeup on this on the Catalina 34 web site. And if you do mounts do all four at the same time. The job is a bit of a pain but doable without removing the galley.

It's true all diesels vibrate. But the difference with new mounts on my boat was nothing short of amazing.