Yamaha 8hp 2-stroke 8MSHR loss of prop thrust

[whereditgo]

I have a Yamaha 8hp 2-stroke 8MSHR that is used in salt water. Last year the motor would work fine at slow speeds, but the prop would slip i.e. dis-engange at higher RPM's. You can hear the motor rev higher when the prop load decreases.

I took the upper and lower apart and found bits of debris from a corroding cast tube that seemed to be causing problems with the lower gear/pinion/clutch. I replaced all the bad components (tubes/seals gaskets, but not any of the gears/shafts as they appeared fine. I re-assembled the motor, but I have the same issue.

It occurs in both forward and reverse. It seems the sprocketed spacer/clutch is dis-engaging from the gears. The upper shaft seems to be fine, as well as the lower pinion/gear spacing looks good.

Any help/insight/tips would be appreciated.

 

[cousinabe]

Re: Yamaha 8hp 2-stroke 8MSHR loss of prop thrust

could the prop have a slipped hub?
have you tried with a different prop?

 

[whereditgo]

Re: Yamaha 8hp 2-stroke 8MSHR loss of prop thrust

Only have the one prop.

Prop hub seems tight, no movement, turns with the shaft (splined).

 

[cousinabe]

Re: Yamaha 8hp 2-stroke 8MSHR loss of prop thrust

put a scribe line on the prop and hub, take her out for a test run. check that the scribe line is still in line.