1959 RD-21 35HP Johnson

[Turbosl2]

I rebuilt the engine last year and it runs great, however today on the water it felt like the prop was slipping under high load and when the boat planes out. It was almost as if the engine would go into neutral but this was not the case. You could reduce the throttle and find a spot all was good. I thought the hub was slipping on the prop but when i removed the prop and put it in the vice on a pin, i could not spin the prop on its hub. It was fastened in there pretty well. You can tell there is rubber there because it does move a deg or 2 but this is with me pulling with full force.

Is it possible this is the problem and it takes more force than i can physically excerpt? I am a pretty strong guy! Or is there something slipping in the lower end that needs adjustment or worn causing the gears to come out of contact. I would think if a key way broke from engaging into gear at to high of an idle the boat would not move at all.

Thanks

 

[F_R]

So you are as strong as 35 horses? Just sayin'. Anyhow, make a mark on the prop nut (or use the cotter pin as a reference). Make another mark on the prop aligned with the first. Run motor till suspected slippage occurs, then stop motor and check marks. If they no longer align, the hub slipped.

There is nothing else in the motor that will slip without jumping & banging or kicking it into neutral.

 

[jimmbo]

Might be ventilating and losing its grip on the water

 

[heypawpaw]

If prop hub is not slipping, tilt motor down one hole and try again, it may help if issue is ventilating.