acts like a slipping clutch

[montara24d]

Have a 1977 25hp Johnson mod#25E77S. While running slow if I crack the gas wide open the motor revs, & it don't go. My first thought was broken shear pin, pulled the prop, & all is good. If I give it the gas slow & steady, all is good, boat gets up on plane with no problem. If I give it the gas all at once it acts just like a car with a stick shift & a slipping clutch. Thoughts?
Thanks, John

 

[sutor623]

Are you already in gear when you lay down on the throttle, or are you just slapping it in gear and rolling out? I would think spun prop hub, but you said shear pin, so there is no hub on this prop?

Any other signs of clutch dog wear? Metal in the gear oil, popping out of gear on its own, hard shifting into F-N or R?

 

[flyingscott]

That prop has a hub on it even with a drive pin there is a rubber hub. Since you don't say it is banging I will go with a spun hub. scratch a line across the inside of the prop take it for a run till it does it. When it does it take the prop off and see if everything is lined up

 

[racerone]

Drive pin is the proper term on that motor.-------Even with a pin most props still have a rubber drive hub.

 

[montara24d]

Happens when I'm running along slow in gear & then give it the throttle all at once. I will remove the prop & scratch a mark, to check for a spun prop, thanks for the suggestion. Gear oil looks good. No strange noise like banging or gear noise. I have owned the motor for five years, we are discussing a 1977 motor, & it could very well be the original prop.
John

 

[ondarvr]

Is this a new issue, or has it been doing it for a long time?

 

[sutor623]

Happens when I'm running along slow in gear & then give it the throttle all at once. I will remove the prop & scratch a mark, to check for a spun prop, thanks for the suggestion. Gear oil looks good. No strange noise like banging or gear noise. I have owned the motor for five years, we are discussing a 1977 motor, & it could very well be the original prop.
John

Cool man, it certainly doesnt sound like a gearcase issue. I think you got lucky and its the prop hub. Let us know how the slip test goes.

 

[montara24d]

Is this a new issue, or has it been doing it for a long time?

This is a new issue. I hope to get to the slip test in the morning, & will post the results.
John

 

[montara24d]

Thanks to all who responded with help, I now know that I have a spun Prop.
Thanks again, John

 

[sutor623]

Cool man, thanks for posting the resolve.

 

[glust]

If it a clutch dog you will know it. When it slips you get a real loud bang like one of your kids is in the back of the boat with a 5 lb sledge hammer whacking away at your floor

 

[glust]

that rubber hub in the prop is like a weak link safety valve. I'd much rather replace a spun prop than hit something in the water and have it tear out a gear or even worse, break a crank or bend the driveshaft. Think what happens when you hit something with the push mower...

 

[Bman2895]

Ive has something similar to this happen to me on a 20hp. I got some weeds on the prop and it wouldnt revup and stay in gear. pulled the motor up and cleared it all off and it was fine

 

[Bman2895]

by prop i meant the front of the foot leading back to the prop