Prop shafts how much movement?

[Ian_Edwards]

Can anyone give me some guidance on how much movement is acceptable in a conventional prop shaft, just aft of the Cutlass Bearing, when the shaft is rotated slowly by hand?

I guess that the movement/play/run-out will be a combination any bend in the shaft and wear in the Cutlass Bearing.

I'm trying to decide whether the shaft needs straightening or replacing or the Cutlass Bearing needs renewing and if repairs are required I'd like to get it done whilst the boat is put of the water for the winter.

 

[Tranona]

There should be virtually no movement up and down or side to side and it should be even when you rotate the shaft. You can usually tell if it is worn because of rumbling noises when running.

 

[vyv_cox]

Don't confuse play with run-out. Pushing the shaft up, down and side to side will detect wear in either the cutless bearing, shaft, or both. A millimetre or so is just about acceptable. Rotating it without disturbing its position in the bearing detects run-out. This should be a very low value, measured at the centre of its length, in tenths of millimetres. The easiest way to check is with the shaft out of the boat, rolled along a flat surface, but the better way is with a gauge.

 

[Ian_Edwards]

Thanks, that's the info' I'm looking for but, just checking that I understand it correctly:

If I put a dial gauge inside the boat about half way between the gearbox and the cutlass bearing, it should be no more than 0.1mm difference when I slowly rotate the shaft by hand?

I shouldn't be able to move the prop (which is quite close to the cutlass bearing) up or down, or side to side for that matter, by more than a 1mm or so?

Is that correct?

 

[vyv_cox]

Thanks, that's the info' I'm looking for but, just checking that I understand it correctly:

If I put a dial gauge inside the boat about half way between the gearbox and the cutlass bearing, it should be no more than 0.1mm difference when I slowly rotate the shaft by hand?

I shouldn't be able to move the prop (which is quite close to the cutlass bearing) up or down, or side to side for that matter, by more than a 1mm or so?

Is that correct?

Yes, you've got it.

 

[Neil_Y]

Bearing clearances will depend on shaft diameter but as a guide so as a guide for Maritex
for a 38.00mm shaft
When new clearance is 0.14mm
You should replace the bearing when it approaches 0.95mm
This calculator allows you to put in shaft and carrier sizes and see our clearances, but these will be different for different bearing materials/makes.