If you own a Hallmark brass SD40-2 made by Kumata or an Oriental E1 set, then you know what this is:
In the Kumata design for these locos, both of the gearboxes are charged (one to each rail). So one of the gearboxes is insulated from the frame. The way they secured it to the frame is with plastic screws.
But they rarely hold. You have to torque them down very snug to get them to hold the gearbox properly...... but when you do that the pressure breaks the head.
This situation is worsened by the fact that they only used two screws per gearbox instead of four. Double whammy.
If you have these locos... you already know all about this... and you know that finding replacement screws is a monumental challenge.
I recently repaired an SD40-2 for someone, and my solution was
--to just toss the old broken/weakened
--tap the two holes for 1-72 screws
--drill two extra holes and also tap them for 1-72
--secure with Walthers plastic 1-72 screws.
Much more secure.
But not everyone feels confident enough to disassemble a loco, and or drill and tap new screws in brass.
So just wish they could find new screws.
Well, I recently came across a source and thought I would share it for those interested.
The company is NBK.
The page for plastic screws is:
https://www.nbk1560.com/en-US/products/specialscrew/nedzicom/plasticscrew/SPE-MC/The screws you need for the SD40-2 and the E1 ATSF set are: M1.6 screws. I would get the 4 mm screws and cut off the excess as needed.
I have not bought from this source yet, but the real reason this interested me is the other sizes.
Kumata only uses M1.6 plastic screws in those two locos (which were their first).
After these first two locos, they switched their design. They switched to all steel screws, but then had to insulate them from the gearbox.
So..... they added little insulating bushings. These kept the screws from touching the gearbox (the gearbox has clear acetate to keep it from touching the frame).
These bushings are in LOTS of Kumata locos. If you own a KMT loco, there's a good chance yours has these.
But once again, there is a problem.
Here is a photo.
The one on the right is still in pretty good shape.
But the one on the left is damaged and no longer useful.
These often split or get crushed.
At present, I have NOT found a source to find the tiny bushings.
The size of the screws is M1.4
Would love to find these bushings if I could.
But what I DID notice is that NBK sells tiny plastic screws.
In fact, they sell M1.4 plastic screws (and smaller!).
I have no idea how strong they would be, but it is nice to know that there is an alternative.
If you have a broken KMT loco, you could removed the steel screws and insulating bushings from the insulted gearbox and replace all four screws with plastic screws.
I may order some in the future to see how strong they are.