Lightwin/Ducktwin Lower Unit

[loggerhead]

I just picked up a ‘55 Ducktwin that needs some TLC and one of the more pressing issues is that the prop shaft is free spinning. In other words, it does not turn when the starter rope is pulled and can be turned by hand with no resistance or noise whatsoever. I seriously doubt that it is the driveshaft splines but am leaning more towards stripped pinion and drive gears or a broken shaft. I’ve never heard of any weak points with these bomb proof little motors but maybe someone else has. Anyone?

[captchuck]

In the time it took you to type this note you can drop the lower unit and have a look. I presume you pulled the prop and checked the shear pin?

[garry-in-michigan]

The shear pin would cause that . . . 😀

[loggerhead]

Well Capitan, I’m a real slow typist…I could have dropped the LU in the the time it took me to read your reply but unfortunately, me and the motor are currently in two different time zones and I believe my post states “prop shaft” free spins and not the prop itself however, just to clarify, with the prop removed, the prop shaft free spins. So no other weak points noted…gotcha!

[david-bartlett]

If someone who didn’t know what they were doing has had it apart and lost, or not installed the thrust bearing properly(#24) in Garry’s picture, it might let the pinion gear drop off the driveshaft and allow things to spin. Just a guess.

[frankr]

There really aren’t any weak points in that lower unit. If I had to pick the weakest point, it would be the driveshaft splines (actually, the crankshaft splines). Hey, there might not even be a drive shaft in there? Some people have been known to take them out and not know the trick to getting them back in.

[need2fish]

I’m not sure how the L/U pinion gear attaches to the driveshaft on that motor (despite having 2 of them), but if it is keyed, perhaps the key is broken (or gone !).

[fleetwin]

Well, I sure hope it isn’t the splines, that would be a shame…Like others have said, there are no real weak points to this gearcase. I understand the engine is nowhere near you, is it yours or someone elses? Any history/info on the engine that might help pinpoint the problem from afar? A pinion/fwd gear failure seems unlikely, unless someone has had it apart or the gearcase has a lot of water in it….

[frankr]

quote need2fish:

I’m not sure how the L/U pinion gear attaches to the driveshaft on that motor (despite having 2 of them), but if it is keyed, perhaps the key is broken (or gone !).

Splined

[retiredoz]

Bet Frank’s right on ! That trick with the driveshaft needs to become universal knowledge !

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