Flex coupling

Hi all,
To make a long story short … I have engine mounting problems. The engine is the Volvo Penta 2002 18HP. I can’t seem to get the engine to stay put. Always going out of alignment. On my recent trip the engine broke an engine mount and spun the cutless bearing.

So I’m looking into a flexable coupling. So far I see an R&D coupling by PYI. Any experience with these or other recommendations?


The probability is that your engine is seriously mis-aligned. If this is the case, a flexible coupling may not resolve your issue.

Flexible couplings are designed to resolve temporary mis-alignments,such as would occur when you are power-sailing the vessel and the hull flexes.

However, a flexible coupling will reduce noise and vibration being transmitted from the engine to the hull.

I have aligned the engine 3 times and runs smoothly for awhile. The problem is it keeps going out of alignment. The VP seems to be a real shaker and no matter how hard I crank down on the engine mounts it eventually goes out of alignment again. Was hoping a flex coupling would help at least when it starts to go out of alignment. I believe I have yanmar engine mounts installed.


I have found the Volvo mounts to be substantially better than Yanmar mounts. For some reason the Yanmar mounts seem to allow a loosening of the nuts, and consequently the locking washers. (I suspect the rubber pads are not dens enough.)

Once the lock is released on the mount, the engine has the ability to move, and will try to spin against the shaft rotation. After a very short time it will either jump off the mount or break the mount. As soon as the engine is off the mount he cutlass bearing is at risk.

Hi Gary and John , I have had some problems steming from a bent shaft on a factory installed 2002 Volvo engine.

I removed and replaced that Volvo with a Yanmar 3GM30F and used a Federal Flexable shaft coupling on the Aquamet 1" ss shaft.

Misalignment and bent shafts are a serious concern. On my BCC the bent shaft caused the cutless bearning shaft log to “De-Bond” from the deadwood area, and allow salt water to enter and migrate down into a damed and filled cavity in the deadwood.

I did want to remove the considerably soft Yanmar mounts, and replacing them with stiffer mounts , but was advised against that, by knowledgable shaft and prop people.

The Yanmar mounts have a different degree of shore for the forward two mounts , than the aft two mounts, and Yanmar reccomends to replace the mounts every few years, but nobody does, even me ! Also Yanmar reccomends using a flexable coupling with their soft mounts.

There is a side benefit for using a flexable coupling , in that it isolates the shaft and prop from engine grounding, through them, so prop zincs last much longer.

I have to install a fixed shaft couple on the shaft to adjust the mounts, then remove that and then install the flexable coupling, to come close, but even just attaching the exhaust hose to the water lift tank will throw out the alignment with the fixed coupling, or even leaning on the Yanmar engine will skew the go-no-go feeler gage test .

There is very little said about “Plunge Thrust” and how to compensate for that force , too , encountered when shifting fwd to reverse and back.

Hope you find something that works for you, as I did !

Thanks Douglas, Thats a big help. actually i was going to check for a bent shaft as the basis of my continued alignment problems. That federal coupling sounds good. Also found out I have the standard Volvo mounts. Do you think it would be worth while to change out to Yanmar mounts?


We just repowered,last year, with Yanmar. The Volvo 2002 had to go and since we did the install ourselves we paid attention to alignment. Scrap the Volvo mounts and put in new ones as I remember our origional mounts were pretty well shot. If your engine is coming out of alignment that often it may be a bent shaft. Are the mounts where they bolt into the bed secure? When we removed the old Volvo mounts one bolt that held the mount down was broken and another was not able to be tightened down.
Bob & Lois
BCC Longsparrow

Hi Gary , I would not put Yanmar motor mounts on your Volvo engine.

There must be Volvo marine engine forum, you could ask there what new mount to use or try to locate a former BCC owner, Marty Chin, in the S F Bay area.