hey guys I'm new to this page and I am hoping a few of you guys can help me out. I have a briggs and stratton 16horse long tail mud motor I bought from a guy that built it. I have no way of getting in touch with him so I'm calling on anyone with any advice..
I'm new to mud motors and I don't know much but for some reason every time I take my boat out it runs fine for about five mins, then the u joint pops off of the motor and I have to jump off and pound it back in to place ..I have key ways and set screws on both yokes . at first I thought it was my prop climbing up the shaft and forcing it off but I've found that that's not the case..I've tac welded them in place and it she added one of my yokes..I'm loosin it guys please help any way u can thanks so much

Something not spaced correctly or out of balance would be my guess but without actually seeing it run its kind of hard to tell. Go run it and take some before and after pics of it when it lets go and post them up, maybe we can shed some light.

Until then, good sharp set-screws. Loc-tite, aircraft safety wire...

Are your keys the entire length of the cut keyway on your shaft, and are your u joints bad?

It's simple. get a mud motor. shoot ducks in the face.

Is the jam nut by the prop walking up the shaft?

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yes the jam nut is sliding up the shaft.its giving about two inches I would say from the prop. when I run it it seems fine but I watch it climb and when I shut the motor off the prop slams back against the end of the shaft forcing the ujoint off the motor. I'll get pics asap for u guys . thanks so much

Anyway to weld it to the shaft tube?

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ya that's a possibility I'm trying to avoid it but that's probably what I'll have to do unless I can figure something else out..I'm thinkn of drilling through the nut above the prop and throwing a pin in that also but I dunno if it will weaken the shaft or not

Don't weld it.. Post some pics up and I'm almost 100% sure one of the folks on here can get you going again. Without looking at anything I agree with SETX that something along the way is out of balance.

If you can't figure out how to post pics, pm me and you can send them to my phone so I can take a look at them. If I can't figure it out I'll post the pics up here and someone will have the answer.

Where are you located?

I think I got it figured out guys..I got some bolt set screws instead of alan wrench so I could tighten them down a lot better I just took it for a spin and it's looking good I also threw a pin through the top nut so my prop isn't moving much at all ..I'm located in northern utah . thanks for all the tips and advice I'm excited to have this as part of my arsenal now..lookin forward ta chatin thanks again