120hp Drive shaft gear case noise

[PaulO]

When I turn the drive shaft over by hand there is a grinding sound coming from the gearcase. It feels a little rough too. There is about .30"+ play in the drive shaft and when it is lifted and turned the grinding sound and feel is gone.

I am hoping when load is placed on the propeller the gear teeth and pinion will raise the drive shaft up preventing the noise.

Has anyone found the same or do I have a problem?

Paul

 

[Frank Acampora]

Re: 120hp Drive shaft gear case noise

Is this a newer Merc built lower? Earlier lower units had the gear thrust downward but later units had gear teeth cut in the opposite direction and the gear load was upward. So if you pulled upward on earlier units, they made noise but quieted when the shaft was pushed down. later units will be the opposite. Later units will have a two piece drive shaft.

In either case, when the gear teeth engage too far there will be a "rumbling" sound and you can feel the teeth meshing. When properly loaded and meshed, they will be silky smooth and noisless.

 

[PaulO]

Re: 120hp Drive shaft gear case noise

Going by my book the lower unit is a type B - two piece shaft, dual exhaust, water intake above the torpedo and the only anode is inside the walls of the housing up near the join seem of the drive shaft housing. It is located to the rear.

I hope this constitutes a later gear box Frank?

I drained the oil and it looked like the contents of a festering abscess. I don't know if the motor had been looked after all that much. It may have been an insurance candidate as the water housing was cracked badly, the impeller had no vanes on it, the lower idle screw was too lean and stuffed the cylinder. There didn't appear to be any leakage from the unit so I will just replenish with new oil and see how it goes.

 

[Frank Acampora]

Re: 120hp Drive shaft gear case noise

Dual exhaust lowers always have the gear load up. there is no locating bearing to keep the shaft from dropping when it is not turning so yes, the gears will grumble until you pull up on the shaft. The bottom of the shaft is carried in a loose roller bearing and the top of the shaft is located by a tapered roller bearing with shims under the cup. It is installed narrow end up and has a threaded ring to hold it against the spacers. DO NOT lose or destroy the shims. They set the gear backlash and they are not available --even at bearing supply stores--even though the bearing itself is standard.

If you are doing the work, might as well check all the seals. Better to invest about 50-75 bucks than to lunch a set of gears due to water infiltration