Greetings
I have a United (PFM) 3-truck class B shay with an open frame DC motor. It runs fine in reverse but going forward it lurches. Can anyone give me a clue as to how I might fix this problem? I appreciate your help.
something in either the drive line from the motor or model gears is binding or somewhere in the pistons and linkage on the outside is binding. Doing it in such a way that it shifts position going backwards illuminating the bind point but going forwards shifts it to a position where it binds. Could this be a known fault with Pfm's not sure. Good place to start.
shane
A pessimist sees a dark tunnel
An optimist sees the light at the end of the tunnel
A realist sees a frieght train
An engineer sees three idiots standing on the tracks stairing blankly in space
Thanks for your reply Shane. I'm going to check that out.
There are a lot of gears and moving parts in that locomotive... Visually, you might be able to see were there is a bind in the power line. If you can remove the cab and boiler, (it's not that difficult to do - just don't drop any screws!), it might be easier to do the detective work. I don't think you can roll the engine on the track without its motor, but you can manually turn the motor and see where the resistance comes from. It might be something loose in the trucks, where the gears from the line move the gears on the wheels.
Simon
Thanks for your reply Simon. I believe I've found the problem. I managed to disassemble without losing any screws. The worm gear coming down from the motor is not aligning properly with the bevel gear under the cylinder block. I can see where there is wear on one side of the bevel gear. I'm going to try to lengthen the screw holes so I can slide the unit enough to center the worm gear on the bevel gear. Wish me luck :)
I'm glad you're making progress. The gear might not be totally shot. It sounds like it results from wear, or an alignment problem. One option is to remove the metal support that holds the motor shaft+gear, remove the screws that hold the motor to the frame, and re-mount the motor with silicone, aligning the gear carefully to the other gear. You might need a few tries.
Posting a picture would surely help to engage others in this conversation.
Hello Simon - I'm not able to post a photo. I have nothing that will focus down that small. I was able to file slots long enough to get the worm gear properly aligned, however every time I tightened the screws the whole assembly shifted over again. I guess I'll have another locomotive on permanent display. I may do what you suggested about re-mounting the motor but if I do that I'll probably just do a new motor. Thanks for your help
Hooray! Success! I was a little discouraged after yesterday, but pressing on I lengthened the motor mount hole and the holes where the worm assembly connects to the frame. After re-connecting everything for the umteenth time I finally have a smooth running shay.
Yeah! Another loco saved from the shelf graveyard. And a Shay!