Securing drive shaft to transmission

[Sunsetrider]

This past week when coming to a dock the boat failed to reverse, then failed to go forward, and I was left adrift. Unable to find any mechanics' assistance I was forced to investigate on my own, hoping the solution lay outside the tranny itself. After manfully struggling to remove the helm seat and heavy engine cover - and balancing it on the cockpit seat - I was able to see that the stainless drive shaft had come apart from the receiver at the rear of the engine. I found that I could slide the shaft toward the hole where it is supposed to enter the tranny. There are two opposing holes in the tranny housing and two opposing holes on the shaft, about 1/4 inch diameter. Obviously for some kind of cotter pin method to secure. So i fished around in the sludge under the engine and pulled out a pin about 2 inches long, perfectly cylindrical and smooth, same size as aforesaid holes! Woopee!

I was able to re-connect the drive shaft and carry on, proud of my intrepid problem-solving . . . but here's the thing: the smooth pin worked into the holes with the assistance of a hammer, but there doesn't seem to be any way to actually secure the pin in position. The pin does not go right through all holes and protrudes a half-inch from the housing. It seems like it wouldn't take much for it to dislodge again. Can anyone advise me as to how this pin is normally secured? Kicking myself for not having taken pictures to illustrate, and reluctant to remove the box just for that purpose.

[jleonard]

From your description I might shorten the pin so it is recessed 1/16 on each side and stake the coupler to retain it.
I have never seen the arrangement you describe. Usually there is a clamping coupling or they are secured with a set screw that enters a detention in the shaft then the screw is locked with a nut and safety wired or both.

[N4QC]

A quick fix might be to take a stainless steel clamp whose size would encircle the coupling configuration. Drill a hole in the center of the clamp band to accommodate the pass thru of the pin. The hole would be placed at the 90 degree point of the clamp band in relation to the clamp’s screw mechanism. When the stainless steel clamp is installed over the coupling configuration, the extended portion of the pin would pass through the hole which was drilled and the head of the pin would be locked in place at a 180 degrees offset of the drilled hole, by the inside of the clamp band.

Regular inspection would be in order…

Have fun,

[Sunsetrider]

The arrangement is per the picture below.

[RobS]

Part # 6 that you originally referred to as a "smooth pin" is what's called a taper pin. Bigger diameter on one end, it's held in place by a snug friction fit. But these require precise tolerances to perform as designed. Your tolerances are likely out of spec now. Along the lines of what Joe posted, if the pin tolerance is still within reason (not a loose sloppy fit), reinstall the pin and then use some form of a band (hose clamp) around the coupler to cover the pin hole(s) and prevent the pin from walking out again. If the end(s) of the pin don't stick out of the coupler once it's tapped back in place then you don't need to drill into the clamp...

[jleonard]

A tapered pin could be secured as Rob described.
If it were my boat I'd pull the shaft and have a keyway machined and buy a new coupler to fit that arrangement.