shaft set screws backing out

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.


Oct 7, 2007
Vessel Make
Bayliner 4550 Pilothouse
So the set screws that tie the shaft into the transmission coupling on my little perkins and the transmission seem to have a special joy in working themselves loose. *When I first bought the boat they literally came all the way out. *I keep a constant eye on them now and they keep coming loose. *There are 2 of them and have a small hole bored through the side of their square heads. *Isn't a wire band often put through that and "tie" them together that way? *I am thinking doing that and setting them with some locktite will help keep them from doing this? *
Simply run a SS wire through the holes and tighten it. Locktite will help, but don't use the permanent type. Chuck
Tony--- See my PM. The safety wire has to be run through the setscrews in a specific direction.
** The wire needs to be run through one bolt then twisted tightly and then wrapped half way around the head in a clockwise direction then to the second bolt doing the same thing. The idea is if the bolt(s) come loose the wire will get tighter holding them in place.

** Next you should check your engine/transmission to shaft alignment. Miss-alignment will cause the shaft to flex at the coupling loosening the set screws. I have seen a shaft that broke were it entered the coupler due to miss-alignment.
Thanks all- I was going to re-wire them but had not thought through the proper way to do it to make sure that the wiring does it's job- due to your helpful replies I will be able to correct this tomorrow!
Safety wiring is a science.* There's the right way, then there are all the other ways.* Here's a link and a pic to show what it should look like.* (In aviation, we take our safety wiring very seriously.)

If you don't have any, drop me a PM with your address and I'll send you some SS safety wire.

IF the screws have backed out the coupling may be in a different location on the shaft.

You will need to lightly drill the shaft under the points of the set screws .

All you need is a small dimple , not the start of a hole .

The drill can be wrapped with masking tape to prevent damage to the coupling .

Then safty wire , monel wire is best, but SS is easier to find.
One of the marina mechanics hooked me up today with some stainless steel wire and the pliers specially made for twisting down safety wires like this- I should be good to go, assuming I did it right! :cowboy:
I wrapped it all up in duct tape when I was done....yes, I wear suspenders AND a belt! haha
I have to ask. I'm new to Trawlers and boats in general. I'm not a boat mechanic, but I work on commercial ships in the engine room. Whenever we put something together, we add whatever the manufacturer says to add to the bolt and then torque it to the proper specs. Sometimes we add a moly lubricant or one of the locktites. But almost every bolt gets torqued. I torque the lug nuts on my car, valve covers, injector hold down bolts, everything. I haven't seen any mention of that in this topic. I'm only trying to learn how to maintain a boat the proper way not insult anyone. Is it that torque is not that critical on these smaller boats, or that it's a given everyone does it so no need to mention it? I realize that the environments are different but bolts are bolts and made to keep things tight. If they come out there is a reason,i.e. heavy vibration due to alignment, age failure, mis-application etc...I have a lot to learn about Trawlers, and I am asking for help in doing things the right way, not trying to insult anyone. Thanks in advance for your comments and input.
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....
You can buy self-locking setscrews (w/nylon patch) thru McMaster Carr online.

Another solution would be to use a locknut in conjunction with a standard setscrew to help prevent backing out.

There is also loctite.

All three together for those who really can't sleep?
Thank you so much*for the info. I see what you mean about the wiring needing to be wound specifically. We use the same method on all bolts for all the pumps on board. Just not on valves, piping or the other peripherals and small auxilliaries.
Top Bottom