Volvo D2-55 Pressure Plate Failure

[Sandy Beaches]

I have just had a disturbing knocking in my Volvo D2-55 potentially diagnosed by the Volvo mechanic. It is possibly a failed pressure plate between the engine and sail-drive gearbox.
We have not yet dismantled things to inspect but it is apparent that is not linked to the actual engine internals such as crank or pistons etc.
I had previously noticed the knock and had listened carefully to try and diagnose (failing of course) but my untrained ear told me it was less likely an engine noise due to the location of the sound.
Stripping the beast down will be awkward and expensive so I will have the mechanic do it.
The mechanic repaired a similar problem on another boat a year ago which was caused by a rope round the prop stopping the motor suddenly. All the load was taken by the pressure plate which failed as a result.
I have never managed this feat in the three years I have owned the boat but it may have occurred under a previous owner.
Any comments or ideas as to the source of the knock would be useful and gratefully received.
The knock does not appear to be absolutely regular but is quite noticeable, sufficient for me to pick it up myself.
thanks all

[Ex-Calif]

Originally Posted by Sandy Beaches

The knock does not appear to be absolutely regular but is quite noticeable, sufficient for me to pick it up myself.
thanks all

Not to second guess your mechanic but I suppose it would depend on the actual sound of the knocking. There are various things that could knock and they would sound different.

I presume he checked

- all engine mounts and SD mounts
- All engine accessory bolts
- Weird things like clearance around engine
- exhaust system security

Was he able to hear and duplicate the knock? Did he use a stethescope? Is there a particular RPM range?

[Sandy Beaches]

I had a long chat with the mechanic to ask most of your questions.
and the short answer is yes to most. I'll double check these things to be sure.
Boat is coming out of the water Friday in any event so we can also check underwater items as well.
Great suggestions thanks.
I scrounge up a stethoscope. It will be a little more accurate than my large screwdriver which worked surprisingly well actually.
appreciate your comments
Ian

[colemj]

That damper plate is not awkward or expensive to replace - unless your engine is so cramped that it has to be removed to access it, of course. One only needs to slide the engine forward a bit so that the shaft decouples from the saildrive, unbolt the damper plate from the flywheel and put a new one on.

Usually, when these damper plates fail, you have no propulsion. Is your prop spinning under load?

This plate is designed to fail should a rope wrap the prop and stop the engine. This saves you from a much more expensive issue!

Mark

[a64pilot]

If this damper plate is like one on an automatic transmission equipped automobile, and I think it is, the damper plate on a car can crack and set up a knock that sounds exactly like a rod knocking, you know that hollow knock that signifies imminent death, any motor head has heard it.
On the automobile one mounting point where the torque converter mounts will crack and set up this knock, you still have driving force and everything works normally, except for this horrible knock.

[Sandy Beaches]

Thanks. I still have normal power so your suggestion works.
Mark is also correct. I will have to slide the motor forward by about 6 inches to separate the two. Then, while access is cramped we can get into the area to replace the plate. This definitely sounds like the fault. The plate kit is apparently around $1400 but I need to double check this.
I'll replace the boot seal around the sail drive leg at the same time as it is the original and 7 years old.
Thanks

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