Clunky prop when engaging forward gear - sometimes

[hoped4]

This season sometimes when we engage forward hear, the propellor makes a significant clunking noise. When put into neutral and then into forwards this is sometimes solved and everything is normal. If it isn't solved first time it usually is second time. The propellor is a Maxprop. I think this only happens after the boat has been in reverse gear and is intermittent. We are being lifted in a couple of weeks and any suggestions of what the cause is would be welcome so We can try to get it sorted. Could it be one of the blades not positioning itself correctly?

 

[vyv_cox]

I think you will find it is the gearbox, but nothing to worry about. When going from forward to reverse gear the intermediate shaft moves forward and back. The clearance is typically .002" but over time this increases a little with wear, causing a clonking noise. Some gearboxes do this from new, others develop it after a time.

 

[hoped4]

Thanks Vyv. I should say that the loud clunking continues until it is put it back into neutral, so can continue for 5 seconds, it feels like it won't stop until you do that. Then when forward is engaged again it either behaves normally or repeats the clunking until put back into neural again.

 

[Caer Urfa]

What Vyv says makes sense but as you are lifting out shortly I would also check the cutlass bearing, the clunking as you call it I have heard before and fades as revs increase as the prop is turning faster
but at slow rev's the shaft will tend to move greater if the clearance in the cutlass bearing is worn.

Another possible sign is are you feeling any extra vibration when standing on the cockpit floor when slightly going ahead

When ashore face the prop and put both hands on it and try to move it side to side, there should be maybe a few thou movement between the shaft and the bearing, if its a mm or more then you have the joy of refitting a new cutlass bearing

 

[hoped4]

Thanks Caer Urfa. I had the cutlass bearing replaced last winter. Come to think of it, I am not sure it happened before it was replaced. Will definitely try your diagnostics.

 

[Richard10002]

Could it be as simple as needing an oil change or, possibly, the wrong oil?