Gibson crankpins

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Stanier6256

Gibson crankpins

Postby Stanier6256 » Thu Jan 02, 2020 3:46 pm

Any ides on how to stop Gibson crankpins from rotating in the wheel boss after assembly?

I have a loco with Walschaert valve gear where the return crank has been soldered to the crankpin and this has loosened the pin in the plastic centred wheel. I am trying Loctite adhesive applied to the head of the screw which can be reached from behind, but is there any other method, short of stripping the whole chassis down and replacing the wheel?

I have got away with this soldering operation on several other locos without any problems.

Philip Hall
Posts: 1328
Joined: Mon Aug 10, 2009 7:49 pm

Re: Gibson crankpins

Postby Philip Hall » Thu Jan 02, 2020 6:55 pm

I always pin the screw in the wheel where it is the centre crankpin if there is Walschaerts about. I drill a 0.45 or 0.5mm hole, using the slot in the screw as a starting point, through into the wheel and then insert a wire pin. This in addition to cyano on a few threads of the screw nearest the head. An alternative is to drill two holes either side of the slot and insert a ‘staple’ into the slot and the holes.

I also make a point of using a brass 14BA screw for this centre pin, because it is much easier to solder the return crank to brass than the steel Gibson screw.

Philip

Dave Franks
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Joined: Tue Apr 16, 2019 9:02 am

Re: Gibson crankpins

Postby Dave Franks » Thu Jan 02, 2020 10:43 pm

A trick that was shown to me many years ago and I've used with success since is to solder a nut onto the crank, clean it out with a tap and then just screw it onto the crankpin and fix with nut lock, no melting of the plastic wheel centre and everything stays tight.

Dave Franks
Back on board.

Stanier6256

Re: Gibson crankpins

Postby Stanier6256 » Tue Jan 07, 2020 11:11 am

I thank the contributors to this thread. No one seems to have noticed that this loco is fully assembled. I am loth to strip it all down as a lot of effort has gone in to making the valve gear fully working. I need a solution if one exists where I have limited access only to the BACK of the wheel.

Philip Hall
Posts: 1328
Joined: Mon Aug 10, 2009 7:49 pm

Re: Gibson crankpins

Postby Philip Hall » Tue Jan 07, 2020 9:22 pm

I did notice that the engine was assembled, and can understand your reluctance to totally dismantle, but where such a problem has manifested itself I think it would be difficult to effect a lasting repair without at least taking the offending wheel off. I presume that the wheelsets are trapped in the frames, not in bearings and hornblocks?

If you can rotate the wheelset into a position where a drill can be got into the slot of the screw, over the top or under the bottom of the frames, that might work. The only alternative would be to drill something like a 0.5mm hole alongside the crankpin (from the front) at a slight angle, in the hope that the drill will go through the head of the screw at some point. The difficulty with that is drilling from a soft material into a hard one without the drill wandering unduly when it hits the crank pin screw. You could then insert a pin with a drop of cyano to hold it in place.

To do this I imagine you might have to remove the return crank, which might loosen the screw even more. If either of these ideas does work, it might be a fragile repair, but then again it might last...

Philip

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grovenor-2685
Posts: 3225
Joined: Sun Jun 29, 2008 8:02 pm

Re: Gibson crankpins

Postby grovenor-2685 » Tue Jan 07, 2020 10:24 pm

Stanier6256 wrote:I thank the contributors to this thread. No one seems to have noticed that this loco is fully assembled. I am loth to strip it all down as a lot of effort has gone in to making the valve gear fully working. I need a solution if one exists where I have limited access only to the BACK of the wheel.

With luck your limited access may allow a drill and pin as per Philip's first suggestion in his first reply.
Failing that I rather think you will have to bite the bullet and dismantle, in which case a new wheel would be the best option.
Regards

Julian Roberts
Posts: 806
Joined: Sat Jan 09, 2010 11:33 pm

Re: Gibson crankpins

Postby Julian Roberts » Wed Jan 08, 2020 7:31 am

There was a lot written on the Forum about return cranks last year on my Crab thread and on one of Dave Holt's loco threads. But not I think specifically on the problem you have. I'm surprised if Loctite isn't the answer. I always find it devastatingly effective - I would worry more about it getting into the wheel bearing and locking that up! If you can unscrew the crankpin as far as you can, put on a drop of Loctite and then screw up again, won't that do it? (You'll be able to do that unscrewing simply by turning the return crank as if screwing it in I think) Make sure everything you don't want to lock up is well lubricated, contrarily that the screw itself is the opposite and totally clean - maybe paint it with white spirit or something equivalent after unscrewing, allow to dry, then apply Loctite and screw back in. Sorry if this may be Grandma sucking eggs stuff. I 24hr-Araldite my crankpins into the wheels and never have any problem with them coming adrift like this - but on the one loco I've made with Walschaerts avoided soldering on the return crank and would always avoid it.

Stanier6256

Re: Gibson crankpins

Postby Stanier6256 » Wed Jan 08, 2020 9:00 pm

Well, thanks again for all your ideas. Which loctite did you use - I used 638.

Julian Roberts
Posts: 806
Joined: Sat Jan 09, 2010 11:33 pm

Re: Gibson crankpins

Postby Julian Roberts » Thu Jan 09, 2020 10:26 am

601 is the stuff I've had for years.

stanier6256

Re: Gibson crankpins

Postby stanier6256 » Mon Feb 03, 2020 3:07 pm

I thought I would let yo all know how this saga finished:

After about six unsuccessful attempts at using loctite I gave up, and tried superglue (also loctite). It worked, though I had a deal of trouble getting the loctite 638 off the end of the head of crankpin screw. Having never hit this unscrewing problem before I conclude that to be quite safe you ought to use a thread locking material at original assembly. Strictly speaking, moving crankpins are only a serious problem on a pin carrying a return crank.


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