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Old 07-28-2011, 10:49 AM   #12
Marin
Scraping Paint
 
City: -
Join Date: Oct 2007
Posts: 13,745
RE: shaft set screws backing out

I have yet to read or hear anyone talk about a torque value for the setscrews on a shaft. When we had new, larger split couplers installed on our shafts to replace the original, too-small, set-screw-only couplers, nobody said anything about torque values for the single setscrew in each new coupler. One of them did back out and the other one would be loose periodically. Turns out the couplers had been installed using non-drilled setscrews. So I called the prop shop we use in Seattle and described the problem and they said bring one of the setscrews down and we'll give you drilled screws (they are hardened steel so they aren't the kind of thing you can dill a hole in yourself with the sort of drill most of us own). They supplied me with a drilled setscrew for each coupler and I safety wired each screw. End of problem. But when we talked about their installation, no torque values were mentioned. It was just "tighten them down real good and wire them."

I'm used to being around jetliner assembly where even the angle a wire is bent to is described in the assembly documentation and regulated by the FAA, JAA, etc. But I think boats--- at least recreational boats--- are WAY more casual in this respect. The engines themselves will have torque values, clearances, etc. called out in the service manual, and probably the transmissions, too. But everything else is just "tighten it down" sort of stuff--- rude and crude and based exclusively on the experience and expertise of the person doing the work.

Of course you can always use the General Motors method of torquing--- tighten it down until it breaks and then back off half a turn. This could account for their reputation as the worst assembler on the planet....
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