volvo penta sterndrive vibrates at low RPM

I have a 4.3 GX-G volvo penta with SX-A 1.79 drive. This was built in Dec 2006 per engine tag. I only have 90 hours on this and purchased it new. I had the alignment checked last year (because of mild low RPM vibration) and was told everything looked good. Over the past 2 years it seems the engine vibrated a bit at low RPMs. I took her out last weekend for the maiden voyage of the year after summerizing with oil and filter change. Ran it in the driveway day before until engine warmed up and had no problems. Engine starts and seems to run ok otherwise. Strong vibration and new clanking sound was noticed after I had been cruising for about 45 minutes. It is most noticable at 800-850 RPM both in gear and out of gear. I don't hear any strange noises when turning the wheel "lock to lock" and the outdrive doesn't vibrate, just the engine. Prop checks ok. Plug wires are tight. Bellows are pristine. Rev it up over 1200 and shaking stops. Hard to tell if noise stops as engine noise overpowers it. It planes fine and otherwise runs fine. I am an hour away from volvo penta repair shop so I was hoping to get an idea of what may be wrong to see if I can fix it myself, or at least know how much it's going to hurt. Oh yeah, I have run this engine over 1000 rpm with drive up in the past before I read it can damage the U-joint assembly but not on this trip.

Re: volvo penta sterndrive vibrates at low RPM

Well, I ordered the shop manual and alignment tool for my boat, removed the drive and inspected the U-joints. All looks and feels smooth and no binding. I began the alignment process and after lowering the front of the engine about an inch it finally slid in and out with very little effort. I removed the sparkplugs and turned the engine 90 degrees and now the alignment tool binds again. After turning the engine several times and fine tuning the engine height to no avail I put the alignment tool into the coupler and had someone turn the engine over. The alignement tool spins as one would expect but it very noticeable wobbles. I fear this means I have a bad coupler. I did find a VOLVO PENTA service bulletin "group 21-3, number 17, version 02" which states that the couplers used in the 2006 engines was faulty and would cause the engine to vibrate at lower RPMs but my engine serial number is outside of their range. Any advice would be appreciated as it look like my vacation fund just fell apart if the coupler is bad.

Re: volvo penta sterndrive vibrates at low RPM

They also adjust side to side, not just up and down. Make sure you've adjusted the engine correctly.

Re: volvo penta sterndrive vibrates at low RPM

When you get the alignment bar, if the alignment is set correctly, turn the engine 90? and check it again, then again at 180? and 270? . If the alignment is ok in all four locations, the coupler is good. If it does change, the coupler is manufacturered off center and could be your vibration.
There is no adjustment for side to side, but engine have been pushed to the side which twists the rear mounts and causes side to side problems.

Re: volvo penta sterndrive vibrates at low RPM

I thought about the engine not being aligned side to side. I did see thicker spline marks on the alignment tool at the 2 o'clock position after rotating the engine 90 degrees. Initially it was at the 12:00 position so I lowered the front of the engine, almost all that was allowed, until the tool moved in and out with little effort. After I turned the engine 90 degrees it came out of alignment. I tried adjusting one side more than the other to see if this would make a difference and it did not. I then loosened the bolts that hold the mounts to the boat and tried the alignment process again.

Re: volvo penta sterndrive vibrates at low RPM

If you had it in alignment at 0, then turn it to 180 and try it, that will tell you how far out the coupler is.

Re: volvo penta sterndrive vibrates at low RPM

well, I hauled my boat to the nearest Volvo Penta auth service center and explained my problem. I got a call today stating that they checked everything out and found no problem at all. Gimbal bearing, Ujoint, drive shaft straight and alignment all ok. I guess I am happy that they are only charging me for an hour of labor. But I still have the problem. I will put it in the water again this weekend and see what happens. Only this time, I will bring my video camera to document what I am seeing. Maybe I am just crazy.