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Old 04-24-2013
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Prop Shaft Coupling

Could someone explain how a prop shaft coulpling stays connected to the prop shaft?

Specifically I am looking at yanmar prop shaft couplings, but I assume they are generally the same as other suppliers.

Yanmar makes 3 types of prop shaft couplings. A straight, a taper and a spit. Looks like the straight and the taper depend on a set screw to resist the longitudinal forces on the shaft (forces that cause boat to go forward or backward). The split coupling has no set screw and looks to resist longitudinal forces by its clamping action.

All couplings have a key and keyway to resist torsional forces.

I ask this question because I have a split couple and the shaft slid forward on the coupling (I have a V-drive so nothing to stop shaft if it slips) about 3/4 inch until the prop started to rub the shaft strut. My coupling does have a set screw threaded hole- but no set screw was ever installed, and yanmar does not show the set screw hole or screw on their drawings or parts list. Wondering why my coulpling/shaft slipped. Were the clamping bolts not tight enough? I will be having a look at the clamping bolts in next few days, but to date, have not tried to tighten them.

The other question is I have seen many times it is difficult to get a coupling of the shaft and you can use a socket between the trans coupling and shaft coupling to force it off. For one thing, this seems like a good way to damage transmission (with all forces involved), but the question is, how would you get this coupling back onto the shaft? I saw somthing on youtube where they heated the coupling in home oven , the slipped it on to get an interference fit. Is this what you do with a sail boat coupling?

Reason I ask is that in the near future, I will be taking my drive line apart, just trying to figure out how it is supposed to be connected.


Last edited by casey1999; 04-24-2013 at 01:56 PM.
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