Serious vibrations on Throttle down

[SUGILITE]

I have a Volvo D2-55 engine that when I throttle down the engine from it will give this horrendous vibration that sounds like the engine is shaking itself apart for a couple of seconds. This happens intermittently, maybe 1 in 20 times and will happen in neutral or in gear. It seems to happen more frequently if I throttle down quickly and doesn't seem to happen if I throttle down slowly. And, of course, I'm never actually looking at the engine when it happens, I'm at the controls.

Volvo had a recall on this engine to replace the dampening plate a few years ago and that was done. I'm suspecting that this issue may be related to the dampening plate -- but if anyone has some experience with this issue, I would appreciate comments.

Regards,

Steve

[sandy daugherty]

Inspect your engine mounts.

[Cheechako]

Sounds like the plate to me. Had a Mercedes diesel in my Passport that did that throttling down, but it always did and was the nature of the beast. It was a great engine other than that, same as the 240D tasi engine that would commonly go 500,000 miles. Cheapest parts I ever bought for a marine diesel too, right from the Mercedes dealer! They must want to keep those taxis going! In 1998 a fresh water pump was about $28 at the dealer!

[Chief Engineer]

Engine Mounts First

Bad dampener plates sound like a can of rocks

[SUGILITE]

It doesn't not sound like a can of rocks. It is a loud shaking shuttering vibration. I'm not currently at the boat, but making sure that the engine mounts are tightened are on my maintenance list which I do a minimum of twice a year for this item and they are tight. At first I was thinking it may be related to the shaft not aligning correctly through the shaft log -- but then I noticed that it would happen even if I was in neutral. Something is not right and considering how pronounced the noise is, I don't think it is helping the engine at all.

[Karletto]

shaft, gears, eng mounts or something inside the eng/ cylinder.

[Celestialsailor]

Maybe use a crow-bar and lift (gently) on the rubber mounts to see if one had a coming apart party.

[SUGILITE]

I want to thank everyone for their suggestions. In an effort to complete this subject for someone else that may have the problem I will document a possible solution.

I disucssed the problem with a local service mananager for Volvo engines. He was very familiar with the problem and said the cause was the low idle speed adjustment was set too low. The fix was to bring the engine up to operating temperature, then idle the engine and set the low idle to 800-850 rpm.

I will not be able to actually try this until I return to the boat next month, but I do remember that the engine does idle around 600 rpm which is quite a bit lower than the recommended speed.

[James S]

Its not just a question if the mounts are tight....try and have a good look at the rubber to see if there is any signs of softening.