Propshaft warble

[IanStew]

I've got a 70' trad with a Ruston Hornsby engine and its developed what can only be described as a warble noise at mid revs. In gear on tick-over it's quiet and at higher revs it's quiet. Any ideas? 

[cuthound]

It's almost certainly the result of thrushing the engine 

[MtB]

I doubt the OP will swallow that one!!

[BEngo]

Get it doing it and then turn the stern tube greaser down hard.  If it stops ( temporarily)  it is most probably some  wear in the stern tube which you will need to assess next time you are aground in a staircase or out for blacking.  My stern tube does this, and has for about 10 years, but the traditional stuffing box  packing isn't leaking and has lasted about 8 years, so there isn't enough wear to justify replacing it.  IMO.

If not it may just be the prop singing.  The dawn chorus does start to get louder this time of year!    Have a feel round the leading and trailing edges of the blades and fair out any major nicks (without taking it too much out of balance).

Other things to check are any intermediate bearings- Thrust bearing, yoke  bearings in a truck-type prop shaft, middle plummer block for a solid shaft etc.- and finally the gearbox back bearing.  The latter will need the shaft disconnecting.  The others should be possible with a  bottle or scissor jack and/or a suitable lever together with a dial gauge or similar.

N