1975 Johnson 25hp. Lost prop on the middle of the lake after hitting rock..

[nwjones18]

Title says most of the story.. Had the boat out on the lake last weekend and while pulling away from the ramp at idle the prop hit a rock hard enough to kill the engine. I pulled up the motor and looked at it and saw no damage, so I started it back up and we were on our way. I noticed on this trip an occasional 'clunking' sound while the engine was under load, almost like it was hitting something under water, but didn't think much of it. Well yesterday took it out again, and this time it was making the 'clunking' sound about every 20 sec while underway and eventually it revved up so i shut it off. Looked back and no prop or nut, and shear pin was bent, but not broken. It was a 3hr troll back. Question is could i have bent the shear pin when i hit the rock, and this be causing the clunking, or do you think I have damaged my gear box somehow?

 

[rockyrude]

Re: 1975 Johnson 25hp. Lost prop on the middle of the lake after hitting rock..

Ideally, the shear pins job is to absorb those kind of hits. They are supposed to be made to break with hits like that. It may be possible a non-standard shear pin was used and why it didn't just break off. I would replace the prop and run it to see if any internal damage happened.

 

[daselbee]

Re: 1975 Johnson 25hp. Lost prop on the middle of the lake after hitting rock..

Klunking like you describe is usually caused by worn edges on the clutch dog and forward gear.
That type of damage could have been caused by the hit.

It requires a re-build of the LU. You MIGHT get lucky and be able to re-machine the face of the dog and fwd gear to make those edges back to factory specs...might not.

Plenty of posts on this board on this subject. Search.

 

[nwjones18]

Re: 1975 Johnson 25hp. Lost prop on the middle of the lake after hitting rock..

Thanks. Sorry I am getting pretty familiar with the upper end of the motor, but the lower unit has been a bit of a mystery to me. I just got out my service manual and looked at everything and now have some understanding of how it works. With the engine off I get no play on the shaft when I have it in reverse and a full 1/4 turn play with it in forward. Would this be considered normal, or a sign of a worn clutch dog/forward gear? Or does it mean nothing at all since the engine isn't running? Thanks again.

 

[boobie]

Re: 1975 Johnson 25hp. Lost prop on the middle of the lake after hitting rock..

The 1/4 turn play is normal. The only way to check the dog and gear is to take the g/c apart.