Vibration

[mike-h]

After constantly struggling (unsuccessfully) to keep the engine bearing bolts tight I'm wondering if the prop and / or shaft needs balancing. When under way there's some vibration which I assume is shaking the bolts loose. In neutral, at all revs, the vibes go. The engine is a fairly recent (Turkish built!) BMC 1.8 which is not the smoothest.

 

How do you know if it is the prop / shaft and if it is how can it be corrected?

 

Advice would be much appreciated

[churchward]

After constantly struggling (unsuccessfully) to keep the engine bearing bolts tight I'm wondering if the prop and / or shaft needs balancing. When under way there's some vibration which I assume is shaking the bolts loose. In neutral, at all revs, the vibes go. The engine is a fairly recent (Turkish built!) BMC 1.8 which is not the smoothest.

 

How do you know if it is the prop / shaft and if it is how can it be corrected?

 

Advice would be much appreciated

I suspect rather than balance of the prop and shaft it is that the shaft may be out of line so that there is strain on the coupling causing vibration.

[Machpoint005]

I suspect rather than balance of the prop and shaft it is that the shaft may be out of line so that there is strain on the coupling causing vibration.

Beat me to it! Yes, much more likely to be misalignment especially since the engine in neutral doesn't vibrate.

[Giggetty]

Beat me to it! Yes, much more likely to be misalignment especially since the engine in neutral doesn't vibrate.

what about severe vibration while idling-disappears above about 1500rpm?

[mike-h]

what about severe vibration while idling-disappears above about 1500rpm?

Dont havea rev counter although vibration varies with different engine speeds. When moored I can turn the prop shaft by hand fairly easily which is why I thought it was out of balance rather than alignment

[RobinJ]

Dont havea rev counter although vibration varies with different engine speeds. When moored I can turn the prop shaft by hand fairly easily which is why I thought it was out of balance rather than alignment

Could be a number of things, a BMC will wobble quite significantly if the valve gaps are out. With a fairly new engine you would expect the flywheel to be balanced, but the drive plate could introduce some misalignment, and depending on the size of prop, a slight misalignment on the coupling could have the same effect.

It is possible to bend the shaft if you hit something hard, but I think you would know about that, so I'm guessing the best thing is to get a strobe lamp and check it with the shaft connected and disconnected and see what the difference is?