Owd-Larrd
Recruit
- Joined
- May 26, 2016
- Messages
- 1
We have a Yamaha 85AET 2-Stroke Outboard dated 1996, serial 688-L-435794-W console steered and driven, on a Humber 5.5m RIB.
Following a friend reversing the boat (when trailered) into a wall (very low speed, low impact) we had a prop-blade missing a corner. Having changed the prop for our spare, we gave it a final spin with our hands, and noticed for the first time the prop's shaft appeared off-centre. Such a gentle prang was not, i'm sure, the cause of the bend we see (thin aluminium prop-blade versus prop-shaft, i.e. case hardened steel bar, surely!!!).
Using gauges and guides, we have measured it to be 0.7mm out on the radius, therefore 1.4mm on the overall diameter during a single rotation. There is zero leakage on the seals, and zero play in bearings holding the shaft.
Google searches i've seen so far say to leave it. If i'm right and this meagre break of the prop tip is not the source of the bending, then for sure we've not noticed it previously in terms of vibration at the helm, or advserse noise, when underway.
Saying that, a concern it it, but I can find no guidance as to what tolerance would be acceptable versus a concern deserving of the costly strip and replacement of the shaft. I accept any off-centre rotation at 5K engine-rpm will cause centrifugal pressure on seals, bearings etc, but how much error, if any, is the norm, versus acceptable, versus a concern worthy of replacement.
Constructive factual help most appreciated,
Sean Mck
on behalf of a SCUBA Diving Club in North West England
Following a friend reversing the boat (when trailered) into a wall (very low speed, low impact) we had a prop-blade missing a corner. Having changed the prop for our spare, we gave it a final spin with our hands, and noticed for the first time the prop's shaft appeared off-centre. Such a gentle prang was not, i'm sure, the cause of the bend we see (thin aluminium prop-blade versus prop-shaft, i.e. case hardened steel bar, surely!!!).
Using gauges and guides, we have measured it to be 0.7mm out on the radius, therefore 1.4mm on the overall diameter during a single rotation. There is zero leakage on the seals, and zero play in bearings holding the shaft.
Google searches i've seen so far say to leave it. If i'm right and this meagre break of the prop tip is not the source of the bending, then for sure we've not noticed it previously in terms of vibration at the helm, or advserse noise, when underway.
Saying that, a concern it it, but I can find no guidance as to what tolerance would be acceptable versus a concern deserving of the costly strip and replacement of the shaft. I accept any off-centre rotation at 5K engine-rpm will cause centrifugal pressure on seals, bearings etc, but how much error, if any, is the norm, versus acceptable, versus a concern worthy of replacement.
Constructive factual help most appreciated,
Sean Mck
on behalf of a SCUBA Diving Club in North West England
