Engine vibration

[Dubo]

Engine vibration(rocking)

I replaced the cutless bearing this winter, since it was over due, and adjusted the strut a bit to lower the aft angle down a tad since there was uneven wear with the old bearing. My first time out I noticed vibrations at varying speeds starting at 1600 rpm's. The engine is a Yanmar 2gm20f.

I viewed many of the helpful post on this site but wonder about this approach to narrow down the problem. I am wondering if this is an engine issue, so I am considering decoupling the flange from the tranny just enough so there was enough clearance and then start the engine and engage the tranny in forward and rev the engine(1600-2400 rpm) for a very short time to see if there is any severe shaking. My thought is if the engine is misfiring or at fault for the vibration it may show up (excessive rocking). I know with no resistance, the engine will run differently but am hoping if the problem is with the engine it might show.

Is this a valid test for the engines steadiness or will this prove nothing?

Thanks for any thoughts.

 

[robertsapp]

If you did not have this vibration before you replaced the cutless bearing and adjusted the strut, and now you do, why do you suspect it's an engine problem?

 

[Dubo]

engine is just a guess

If you did not have this vibration before you replaced the cutless bearing and adjusted the strut, and now you do, why do you suspect it's an engine problem?

I went below to witness the source and it seemed like the engine was rocking and the shaft seemed to be stable. The boat has a packless shaft seal which allows for movement of the shaft and there wasn't much. I'm no expert but I would think if the problem was in the shaft it would have gyrated more...I've been wrong before.

 

[robertsapp]

Re: engine is just a guess

Well I certainly don't know what the issue may be, but Occam's Razor says that if everything is fine, and then you change something, and now everything is hosed up, the odds are whatever you changed is most likely the problem. Good luck, hope you work it out soon and can get back to sailing.

 

[Benny17441]

It may not prove much by itself as the engine is not under load. I would conduct another test and that is to take the boat sailing in a brisk breeze and leave the transmission in neutral and the let the prop and shaft freewheel. Listen, feel and observe for any vibration from the spinning shaft. This may point to the shaft alingment or propeller issue or if it turns smoothly will indicate is an engine problem. You need to get going to 5 or 6 knots under sail preferably opposing any current.

 

[navigator97]

I would also check the engine mounts while the engine is running to see if one or more mounts may have loosened some. If not continue to look elsewhere. Since you "shimmed " up the strut some (my inference from your comments) that must have changed the shaft angle slightly. Perhaps unloosing the bolts in the shaft coupling just aft of the transmission and re-tightening them may allow for some re-alignment. Thoughts to ponder.

 

[Dubo]

It may not prove much by itself as the engine is not under load. I would conduct another test and that is to take the boat sailing in a brisk breeze and leave the transmission in neutral and the let the prop and shaft freewheel. Listen, feel and observe for any vibration from the spinning shaft. This may point to the shaft alingment or propeller issue or if it turns smoothly will indicate is an engine problem. You need to get going to 5 or 6 knots under sail preferably opposing any current.

Benny,
I did take her out yesterday and was surprised that the shaft did spin sooner than normal. This was evident pretty soon once the sail was raised. The fact that it was sooner than later like last year gave me the impression there was less resistance on the shaft from the bearing/strut.

I am trying to avoid spending hours trying to align the engine if the issue is with the engine itself(bad fuel or injector or whatever). I already know the alignment is slightly off but I wanted to do a trial run before attempting the alignment route. My thought of the engine needing attention was my attempt at eliminating another variable. I did replace the secondary fuel filter with a 2 micron filter. Could the engine be starved for fuel or would it stall?

 

[robertsapp]

An engine that's starved for fuel will slow down, as if the throttle is closed. It shouldn't run rough - that would be another problem.

I really do think this sounds like that old joke where the guy looses his keys in the parking lot, but he's looking for them over by the street light because the light's better there. If the engine runs smoothly at various RPMs in neutral, and only vibrates when in gear, you most likely have an alignment problem, and since you recently changed the alignment, well, that's where I'd be concentrating. Now if the engine kicks and coughs in neutral when you try to run up the RPMs, then you may be on to something.

 

[Dubo]

Yeah but Robert I may have dropped my keys by the light! Point taken though. I do agree with your conclusion that the alignment is the likely cause for the vibs since things have changed with the shaft...especially the strut. Thanks for keeping me on track! Time to get out the knee pads and learn new curse words.

 

[robertsapp]

Please tell us what you find. As you learn, we learn, and having learned, pass the knowledge forward.

 

[Cool_Change]

The alignment shouldn't be off at all. It takes very little misalignment to create vibration thru the drive train...

Also agree with the suggestion of checking and potentially just replacing the engine mounts. I did mine before on our previous h27 and was amazed at how much quieter it was and significantly less vibration that we had just gotten used to!

 

[onecoolair]

Re: Engine vibration(rocking)

Had this happen once. One weekend everything was fine the next weekend had a terrible vibration when I put it into gear and went past idiol. Did a quick haul needed a power wash on bottom anyway, as prop came into view there was the biggest dang clam I ever saw clamped down on one of the blades of my 3 bladed cruising prop.

 

[SVCarolena]

As others have said, allignment can make a big difference. I know from experience, and in fact realigning really isn't that tough, just a little time consuming. As also suggested, check your prop just to be safe (it is always possible it got dinged at some point). Also, before you spend the time on allignment, how are the motormounts? Yanmar considers them to be a wear item. We replaced ours last year and it made a huge difference - it runs like a different boat. They are expensive, but depending on the age of your boat, it may be time. If the mounts are worn, you will have a hard time getting it alligned correctly. Also, if you ever do decide on doing the mounts, I highly suggest going with the Yamar originals, despite the cost. I've heard lots of stories of people using aftermarket mounts and eventually going back to replace them with the Yanmars.

 

[onecoolair]

Does the replacement yanmar mounts rust as bad as the originals? Keep cleaning painting them. But to no avail......AAARRRGGGhHHHH!!!!!:cussing: