Male pilot coupling optional for output flange? - SailNet Community
 
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post #1 of 2 Old 07-31-2009 Thread Starter
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Male pilot coupling optional for output flange?

All,

The mechanic that re-powered our 33' ketch left the old prop shaft in place with the old (Volvo) coupling which has a female register and bolted that up to the new ZF Hurth output flange which also has a female register. See photo named 20090729... of both pieces on the workbench in the boatyard.

I'm thinking that maybe, just maybe, there should have been a male pilot on that shaft coupling to not only center it in the output flange but KEEP it centered. And that the lack of a male pilot coupling led to the prop shaft coming OUT OF the coupling after 90 hours running time when I put the gear in reverse. The set screws, with wire holding them, were solidly in place, and the boatyard is saying the shaft came out due to misalignment which was due to no pilot going into the output flange register.

As an aside, the transmission output flange has been 'fretted' or compromised as a result of the misalignment, meaning just a coupla thou more to replace it - no big deal!

Photo 20090730 is of a newer coupling on the left with the male pilot that should have worked but did not, the boatyard is telling me, because the transmission flange had not been compromised. Again: coupling on the left is what my original mechanic SHOULD HAVE used; female coupling on the right is what he DID use and what I think failed.

My mechanic says though that this male pilot is optional, that it's just the opinion of this yard that it's needed. Even though the transmission output flange is obviously designed for a pilot, he still says it's optional.

Question: does anyone have a link to any industry standard requiring a male pilot coupling be used with a female register flange? It may be a no-brainer, but I need some documentation to back up my case.

That is unless the consensus in this forum is that this should have held, should have been sufficient. We're talking about a fairly small coupling, 4" diameter, and a 33HP motor.

Any input would be appreciated.

Thanks
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post #2 of 2 Old 07-31-2009
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i installed many couplings over the years when i worked for cummins diesel. couplings are designed so the male pilot fits snugly into the female coupling. that is the only thing that keeps it in alignment. you can't rely on the bolts to hold it in alignment. i always aligned the shaft to less than .003" and never had any problems. i would be happy to answer any questions.

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