A little give on the shaft?

[saxguy73]

So after buying a used sterndrive last summer, I just changed the prop for more stability and torque, however, when I tried to move it, it gave just a little on the shaft, maybe 1/16"-1/8". I have checked all parts, removed the prop 3 more times, checked the thrust washer etc, but the same result. Prior to installing the prop nut, I put pressure on the aft adapter and the prop did not move at all, but when I finished torquing the nut (55 ft lbs), same result. Am I getting frustrated over nothing, or is this a real issue. TIA!

 

[Scott06]

So after buying a used sterndrive last summer, I just changed the prop for more stability and torque, however, when I tried to move it, it gave just a little on the shaft, maybe 1/16"-1/8". I have checked all parts, removed the prop 3 more times, checked the thrust washer etc, but the same result. Prior to installing the prop nut, I put pressure on the aft adapter and the prop did not move at all, but when I finished torquing the nut (55 ft lbs), same result. Am I getting frustrated over nothing, or is this a real issue. TIA!

What outdirve are you working on? For example a merc alpha drive when in neutral the prop shaft moves in and out a 1/8” or so. Im wonderingif the propis tight to shaft and its just normal endplay in prop shaft

 

[saxguy73]

What outdirve are you working on? For example a merc alpha drive when in neutral the prop shaft moves in and out a 1/8” or so. Im wonderingif the propis tight to shaft and its just normal endplay in prop shaft

It's an Alpha 1, and that would ease my mind about the situation if that would explain it, thanks.

 

[Scott06]

It's an Alpha 1, and that would ease my mind about the situation if that would explain it, thanks.

When the prop moves in and out look at the nut I bet the nut and shaft is moving with the prop. Its a common thinking this is an issue, has come up many times on this forum

 

[Texasmark]

Some Mercury engines have a built in "overrun clutch" built into the rear of F gear and the front of the "clutch dog" that rides on the Prop Shaft and is positioned along the prop shaft by the shift linkage, selecting FNor R gear.

On these some Mercury engines, there is a sawtoothed arrangement, just like the teeth on an old hand saw...slow rising slope and abrupt steep fall and as you turn the prop CW (looking from the rear) the Prop Shaft will move slowly in or out...forget which and suddenly fall back to where it was as the clutch dog rides up on the peak of the slope and falls back to start over. When turning the prop CCW while in F gear, the Prop Shaft locks to the Drive Shaft as this is the direction used when the engine is driving the propshaft.

This overrun clutch is like one in a tractor whereby you have an implement full of Kinetic energy spinning on a rotary mower for example and you want to shift gears...you need to disconnect the implement...or prop that is being driven by the water flowing past it.....so that the engine can slow down and not be "force driven" by the load.

I just learned this week that since around 1996 or thereabouts, Merc. V6 OB engines no longer have this feature. Guess what if you are blasting along at 65 MPH hooked up on your pad and all that great stuff and immediately shift to N...meaning the engine goes from WOT to idle in a heartbeat, you had better be hanging on because the Prop Shaft is locked to the Drive Shaft and it will essentially stop spinning and you have this 14+" diameter speed brake bring your craft to a speedy stop. The same person that mentioned this also said that you get used to it. Well I don't know if you get used to your teeth getting stuck in your windshield on panic stops!!!!!!!!

In short it may have the slip clutch feature and is perfectly normal. The R gear is vertical sided cogs and slots so shifting to R (only if the engine is running or you are rotating the prop while you shift) ...getting the cogs and slots lined up, it will lock in both directions.