Play in drive shaft

[Tom6002]

I am replacing the impellor in a 1991 8 HP Johnson, and everything seems to be going well except that there is about 270 degrees of play in the drive shaft. I mean that if I turn the shaft until the prop turns, then reverse the rotation and twist it the other direction you can rotate the shaft about 270 degrees before the prop will turn in the opposite direction. Is something screwed up in the lower unit?

 

[Vic.S]

Re: Play in drive shaft

I dont thinkink you are finding play in the driveshaft as such. At least I hope not. What you are noticing is the backlash in the dog clutch. There should be no play between the crankshaft and the driveshaft

It is possible to freely turn the prop of my 6hp about 90?. With a gear ratio of 13:29 that would be about 200? at the flywheel.

 

[F_R]

Re: Play in drive shaft

I am replacing the impellor in a 1991 8 HP Johnson, and everything seems to be going well except that there is about 270 degrees of play in the drive shaft. I mean that if I turn the shaft until the prop turns, then reverse the rotation and twist it the other direction you can rotate the shaft about 270 degrees before the prop will turn in the opposite direction. Is something screwed up in the lower unit?

Tom, when the motor is running, there are two gears, forward and reverse, spinning in opposite directions inside the lower unit. A part called a clutch dog slides between those opposite spinning gears to couple them to the prop shaft. Now, imagine this: Suppose there are a string of cars zooming down a road and you want to pull between two of them without getting mashed to bits. Obviously, the farther apart the cars are, the better chance you have of doing that. Likewise, the farther apart the lugs on those gears are, the better chance you have of getting the clutch dog slipped in between them without clashing. That is why the designers leave such a wide gap--which you perceive as "play". It's normal and necessary that it be that way.

 

[Tom6002]

Re: Play in drive shaft

Thanks for the responses.