yamaha lower unit

[hop3307]

I have a 1987 70 h.p. yamaha that came with a used boat purchase. The boat had not been used for about 3 years and the previous owner had replaced the lower unit with a "low hours unit". While on the trailer hooked up to a hose the motor will go into all gears with some slight grinding shifting to forward. When I put the boat in the water it will not shift to forward and grinds terribly. Reverse and nuetral work fine. I drained the oil and it was quite metalic but no large particles. Any help would be greatly appreciated.

 

[Capt Ken]

Re: yamaha lower unit

The shift shaft that goes from the engine down to the lower unit is probably rusted almost in half. Units pior to 93 have steel shift shafts and 93 and new have stainless steel ones. What happens is the shaft gets so rusty on the bottom end that the shaft twists and you lose either forward or reverse. If you remove the lower unit and look up at the shift shaft, you will see just above the coupling the shaft rusted almost in half. There is probably nothing wrong with the lower unit. I've seen owner's take their engines to mechanics not familiar with this problem, pay for a complete rebuild and still have the problem.

 

[hop3307]

Re: yamaha lower unit

Thanks for the info. there is asubstantial amount of corrosion exactly where you said it would be. Do I need to take the power head off to fix it? Also I'm still a little concerned about the amount of metal in the oil. thanks again for the help!

 

[Capt Ken]

Re: yamaha lower unit

The powerhead will need to be removed to replace the shift shaft. Its the lever under the bottom carb and the whole thing pulls out the top. As for the metal, I would change the oil and run it. At this point if the unit is self destructing, nothing at this point can help. It could be metal from the unit not engaging quickly and wearing off the edges of the clutch dog.