Mystery engine vibration, gear box failure?

[WindermereColvic]

Hi Everyone, Our Sole Mini 26 has developed a severe vibration in the for-aft direction (side to side and up-down remain vibration free) when in forward gear. As we increase revs, the size of the vibrations increase to the point that at cruising speed the engine and shaft assembly is moving nearly an inch on its mounts, many times a second. Oddly, when in full ahead at 3400 revs say, everything is fine and normal. For this reason, we do not suspect a damaged prop or shaft. We have been told that perhaps the clutch cones in the RONIM V gearbox are worn and slipping, until sufficient thrust is applied in full ahead to hold them together. Accordingly, we have removed the gearbox ready to change them. Before its striped though, i thought ide ask on here to see if anyone has any other theories about our mystery vibrations, or any advice as what to look for in the gearbox. Thanks, Matt

[timebandit]

I think it is you engine mounts.

[Mipcar]

What sort of prop are you running? I had vibration (not as bad as you describe) but only at certain revs. In my case I found it was my geared feathering prop binding and not setting properly under power.
Once I fixed it that problem was solved.

Mychael

[Maine Sail]

It could be many things:

Bent prop
bent shaft
misaligned
bad motor mounts
loose motor mounts
slipping transmission
loose coupling (failed tolerance between shaft and tranny)
Failed cutlass bearing
Loose strut
Bad engine valve, timing, fuel adjustment causing engine vibration in concurrence with shaft issues.

or a combination of any of the above

[WindermereColvic]

Thanks for everyones help so far.
Is there an easy way to see if the mounts are ok? Ive been told i could just try and lever the engine up, and if it moves then the mounts have failed, does this sound reasonable?
Most of the things suggested by Maine Sail have been discounted, but im starting to wonder if we have been too hasty. This is why we have discounted them, does this sound ok?
Bent prop-Visually inspected, no impact ect since it all worked
bent shaft- visually fine, and runs fine at full RPM
misaligned- has been realigned to check
slipping transmissionthis is what we think it is, but its proving hard to find anyone willing to test our gearbox
Failed cutlass bearing - Shaft will not wobble by hand, squeeks healthily
Loose strut- Which strut?
Bad engine valve, timing, fuel adjustment - engine runs fine in neutral and reverse.

Thanks again, Matt

[bigcj39]

have somewhat same prob.helped when i found prop was bent.reworked prop.helped some but not complete.thinking maybe bent shaft.vibration was at 1100 cleared up at around 1300rpm.

[dieselboy]

May i ask a question for your question?

Diesel or gas?

If Diesel and it is a multi cyl engine i would look for a weak or dead cylinder.
You can use a temp gun at each exhaust port and read temp " with a temp gun" if there is more than say 10% diff on one cyl you may have lost an injector,or valves out of adj.

A diesel when un loaded will run fine, its not till you get to a lugging situation that it will be felt then as rpm's come up the engine will smooth back out.

Just more food for thought, as if you needed more.
Good luck.

[bigcj39]

Thanks.Ill be checking this out soon and ill post my findings.

[RichH]

FIRST, check the prop for attachment of barnacles, damage - bent or warped prop, 'rope' wrapped around the exposed shaft.

Attachment of 'weight' to a prop can change the 'vibrational frequency' and that vibration can occur at only low speed and other 'mathematical nodes' (resonance).

Check the Prop FIRST as its the most common cause of vibration .... and its usually barnacles or other 'attached growth' that causes the 'vibration'. Barnacles along the whole east coast this season are - incredible.