I have a LT GD with a Kohler 25. I took off my old worn out prop before Teal season and replaced it with a new one from GD. The boat ran great by myself, but as soon as I brought a buddy with me I noticed a slapping noise that sounded and felt like it was coming from the U-Joint area. I noticed that my upper seal was egg shaped, so I went ahead and replaced the upper and lower seals, seal caps, and shaft, but still had the slapping noise when I put it in the water with a full load. I figured then that it had to be coming from my U-joint, so last saturday my neighbor and I replaced the 4-way U-joint. I put it in the water and am still getting the same damn clanking noise. I can feel the noise through the handle when I'm running it and the motor misses whenever the noise happens. My neighbor who is a retired nuculear millwright and I are at a loss. Figured I'd run it by y'all for some fresh opinions on what it could be that's causing the slapping noise. At this point, I'm praying it isn't at the crank shaft.


Background on the motor:

-'96 Kohler 25 and '96 frame
-643 hours on motor
-Slapping noise only happens when under a full load or heavy vegetation or making a sharp turn wide open
-Has always ran strong 3200 @ 20mph currently(need to adjust throttle cable)
Has a crack at one of the exaust manifolds at the motor

Appreciate any help

From what you have described, it would seem to me that if the seal was oblonged it would only make sense that the bushing or bearing would be worn in the same fashion...?

Check for a bent shaft


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Did you put your prop on like GD says in instructions with 1/4 turn play? If so, could be your prop. That noise is normal. Old prop could have been rusted on, new prop spins freely.

Do you mean 1/4" of play for the prop in between the lock nuts and the prop nut? If so, no, the lock nuts and the prop nut are pretty tight against the prop.

When I first got this motor it was making this same slapping noise but not as often, but eventually it went away. Probably went away as my prop wore down.When I put the new prop on is when the noise came back.

Run it with the prop off, does it still make noise?

Wondering about prop balancing?

The prop "floats" a 1/4 TURN on shaft
Yes they make a loud pop/crack when you put it under load or pull it outta the water. Normal

Cajun, It won't make that noise with the prop off. About two months ago I took my old prop off, which was about the size of a trolling motor prop, and replaced it with a new one. That is when the slapping noise started happening again. Seems the more the motor is under a load the more something slaps.

PostPaul, I really don't think it's normal. I've only owned 2 LT's, but I've run a few and haven't heard that noise before. That being said, i don't have a 1/4 inch of play around my prop, and never have. Even if I wanted to give the prop a quarter inch play there isn't enough shaft at the prop. I'm going scoutin in the morning. I'll try to take some video of it making that noise and pictures of the prop and all.

Appreciate it.