Yamaha 30HP over-revs at acceleration

[JP Richmond]

Hello all,

In have a 1989 30LF on my jon boat. I hit a small bouy/line yesterday and about 30 minutes later, as we were pulling a tube, it revved a few times crossing a wake and within ten seconds it lost all high-speed torque. It wouldn't accelerate past a fast crawl without over-revving and losing torque. I crawled it in and it brought it home. Ran fine at really slow speed.

Figuring the impact was the cause (vs. fuel and other causes, coincidences being rare), I pulled the prop, looking for a signs of a "slipping forward thrust hub" (internet research).

The prop is banged up a bit, with the forward rim missing a small piece and bent in one spot. Looking into the forward end of the prop, I see chewed-up looking rubber surrounding the "spline channel" (my term). The thrust hub is just a large washer, all metal, and I don't see any way it can "grip" or "slip", since it rides the shaft forward the splines.

I drained the gearcase, and the oil is fresh with no evidence of water or metallic particles.

Any suggestions?

 

[btruong]

Re: Yamaha 30HP over-revs at acceleration

i would put my money on a spun hub. the hub is the black rubber that connects the "spline channel" to the prop. it is there in case, as in your situation, the prop hits something. the prop hit the buoy and stopped, the torque of the motor kept the shaft spinning, and the hub just "breaks free" of the prop to prevent any damage to the gearcase. so now the propeller shaft spins, and as it spins faster, the hub isnt gripping onto it so the propeller isnt spinning along with it. so the engine revs up but no thrust. well thats my understanding. i would recommend a new prop. my 2 cents.

this should help:
http://www.mercstuff.com/spunprop.htm

 

[JP Richmond]

Re: Yamaha 30HP over-revs at acceleration

Thanks, btruong: You are correct. I'll get a new prop...need to rethink pitch, but I think I need to start a new thread for that... JP