Potwarp Stalled my Yanmar

[Seagull111]

Now my yanmar vibrates when idling whether in or out of gear. It smooths out at higher (1300+) rpm. The engine mounts spit off quite a bit of rubber coating when I hit the lobster pot but the engine doesn't seem to move around under load.the shaft, bearing, Cush drive, and engine mounts are 1 year old with about 200 hours. The diver said everything looked ok. The eng/ trans used to rattle at idle when in gear but now shakes noisily. What have I destroyed?

[roverhi]

The stock Yanmar mounts appeared okay on my engine before I pulled it. Found the mounts to be delaminated and barely holding on when removed. Could be you ripped the rubber away from the metal when the warp stalled the engine.

Does the engine shake just at idle or low rpm in neutral or in gear??? If it's worse or only happens in gear, could be a bent shaft or prop damage.

[GregSteimel]

Sounds like a bent propeller shaft

[Seagull111]

It shakes badly at low rpm in or out of gear? It is quite smooth in or out of gear at 1800 rpm or above.

[foggysail]

My guess is motor mounts. If you have a shaft problem, I believe vibrations will be worse at higher RPMs.

Getting back to motor mounts and I do not know what you have on your boat. I have seen a collection of junk engineering over the years for mounts. There is no one motor mount for all situations. For example, those mounts with adjustable heights change the fulcrum point via the set heights. Remember, the forward & reverse loading created by the engine is transferred to the hull via the mounts.

A better solution to the height adjustment problem is to shim the mount itself rather than to have a threaded rod type adjustment.

Some more info on mounts. They are designed for both horizontal and vertical forces along with vibration isolation. In fact, mounts have their own frequency resonances. This means if a vibration frequency of say 500 Hz at 2Gs is applied to the mount that has a resonance at that frequency, instead of damping the applied vibrations, the vibrations will be amplified making it much worse.

Enough for motor mount engineering. If your engine vibrations were acceptable before the prop got tangled, you might be wise to just replace them with parts that have similar ratings. When the boat is out of the water, you can if needed have the shaft checked.

[perchance]

Depending on the rpm at the time of the incident and wether the engine slammed to an abrupt halt will determine what damage was done. It could be the engine was thrown out of alignment, bent prop shaft or ruined motor mounts (not fan of flabbyYanmar mounts as the Vulcanisation and design is poor in my opinion).
Continuing to run the engine with an out of balance prop shaft will eat the Cutlass bearing and eventually destroy the out put shaft seal on your transmission

[Seagull111]

Thanks all for the insight. Pulling the boat next week to check it out.

[Jim Cate]

If the vibration exists when the tranny is in neutral then it can not be from the shaft nor from misalignment issues.

It is unlikely that anything within the engine could be causing it.

Motor mounts are left as the likely culprit.

Cheers,

Jim

[Cotemar]

Its the motor mounts delaminated from the metal.
Buy new ones

[Seagull111]

Originally Posted by Cotemar

Its the motor mounts delaminated from the metal.
Buy new ones

Hauled the boat, found a loose shaft zink and the yard found that the flex drive had been yanked out of whack. Hope that fixes it.

[Jim Cate]

Originally Posted by Seagull111

Hauled the boat, found a loose shaft zink and the yard found that the flex drive had been yanked out of whack. Hope that fixes it.

Don't understand how either of these can solve an engine vibration that occurs when in neutral... ie, shaft and coupling not rotating. Can you explain their logic in this fix?

Cheers,

Jim

[Seagull111]

The flex drive was stretched to the point where it held the engine slightly up and off center on it's mounts so that at low idle and shutdown it shook more than a normal idle. It is fine now that it is aligned properly on it's mounts.

[Seagull111]

The stretched flex drive was forcing the engine against the engine mounts and the misalignment made the shaking at idle and shutdown seem worse than it was. It is ffne now.

[Jim Cate]

Originally Posted by Seagull111

The stretched flex drive was forcing the engine against the engine mounts and the misalignment made the shaking at idle and shutdown seem worse than it was. It is ffne now.

Sheesh, that's one buggered flex drive! Thanks for the explanation for it was bugging me. Glad that your problem is solved.

Jim

[Seagull111]

There is an interesting link to yanmar engine mounts on the PSC forum on sail net. It seems that the highest amplitude of engine shaking is when the engine is shut down or the idle is set too low. I think when I tangled the pot warp and I tried to idle the engine before it stalled that the twisting of the engine pulled the throttle cable a bit and reduced my idle speed which caused the increased shaking of the engine even in neutral. A small reduction in idle speed can make a big increase in shaking amplitude. I didn't notice it right away and this is why I didn't understand why it smoothed out even in gear at higher rpm. So perhaps the mangled flex drive which left the drive shaft 1 1/2 inch aft ,where is was yanked by the pot warp, wasn't increasing the vibration after all .