Overland Models E7 Diesels (truck binding)

[ChristianJDavis1]

I inherited two  CB&Q E7A locomotives which seem to both have problems with the front truck. Both units run and make a clicking noise like they have a cracked gear (which they both do on the same axle on the same truck) and the gears in the trucks themselves bind causing the locomotives to "hop" until they either bind completely or derail themselves. I've taken apart the offending axle (rear axle of front truck for both units) and put them back together, but that didn't seem to help at all. The axles are a plastic axle, with a plastic gear with two metal sleeves that include the wheels (going together like this: |= - I - =| ). It seems like once per revolution, they bind, but in the same spot each time. The thing is, the way the trucks are assembled, it is very difficult to get all of the axles and gears out; the actual truck is all one piece with the gears and axles pushed in from both sides to sandwich the gear/axle assembly. The rear trucks do not exhibit this problem, and I'm sure if I swapped the rear truck from one to the front of the other, I'd get one functioning unit, so I'm unsure if this is some manufacturing defect or a coincidence it just so happened to occur twice between units on the same axle on the same truck while rendering the entire truck useless. Basically, I am coming to you guys to either 1: ask if you have seen anything like this before, and 2: ask if anybody has any ideas on how to fix it.

[garethashenden]

If they have cracked gears the solution is to replace them. Since the teeth are slightly farther apart at the crack the gear doesn't mesh properly. I don't know if the gears are available, but I'd start there.

[ChristianJDavis1]

If they have cracked gears the solution is to replace them. Since the teeth are slightly farther apart at the crack the gear doesn't mesh properly. I don't know if the gears are available, but I'd start there.

I figured I would have to replace them, but the truck binds with those gears in or out (meaning another one might be cracked in there and I'm not exactly sure how to get to it). Maybe I should try pulling as many out as I can and see which one being removed causes it to stop binding.

[garethashenden]

It seems like once per revolution, they bind, but in the same spot each time.

If you mean once per revolution of the wheels, then its probably the axle gears. Assuming the other gears are different sizes to give a reduction in speed. There might also be something in the gear. I had a bit of ballast in between the teeth once that caused a bind.

[ChristianJDavis1]

If you mean once per revolution of the wheels, then its probably the axle gears. Assuming the other gears are different sizes to give a reduction in speed. There might also be something in the gear. I had a bit of ballast in between the teeth once that caused a bind.

Upon inspecting it again, I believe you were correct; it is that cracked gear. Replacing the axle minus the gear allows it to run no problem (but there is a squeaking issue that I'm sure is a result of the metal axle rubbing against the surface of the truck where it inserts into the truck). So with that, I have to find new gears (this should be fun). Nine teeth with a skew to the teeth, no way to take a measurement of it at present.

[ChristianJDavis1]

So both of them run now minus that gear (I guess for the time being I will have to give up some pulling power in order for them to move at all). Will lube the axles where they enter the truck to see if that can fix the squealing. I find it very odd that the exact same axle gear went bad on both units.

[BrionO]

If the locomotive was made by Samhongsa it is a cracked gear for sure.  The nylon gears would shrink over time and were notorious for cracking.  Back in the day Samhongsa furnished replacement gears made of brass.  That's the only fix.  If you can't find factory replacements maybe Northwest Shortline has a solution.

[ChristianJDavis1]

If the locomotive was made by Samhongsa it is a cracked gear for sure.  The nylon gears would shrink over time and were notorious for cracking.  Back in the day Samhongsa furnished replacement gears made of brass.  That's the only fix.  If you can't find factory replacements maybe Northwest Shortline has a solution.

Overland Models by Ajin; different animal than the Samhongsa-built Oriental Limited. Samhonsga trucks are at least easy to take apart, but usually the gear that goes bad in those is the one in contact with the worm. The overland models, seen here (http://www.spookshow.net/loco/omie.html) are almost like a Kato/Atlas locomotive with how they are build aside from the trucks, which are like nothing I have ever seen before. Once I can get my calipers, I will be taking measurements of the gears to see if I can't find anything to replace it with.

[nkalanaga]

If all else fails, you could try 3D printing new gears.  They might not be as durable, depending on the material used, but you could print enough to be able to replace them for years to come.

[mmagliaro]

Here's the place I've pointed to for gears a few times.  I bet they have what you need:
https://shop.kkpmo.com/index.php

If you take measurements (diameter, number of teeth, bore, and thickness), you can calculate the module and then
pick out the gear you need from the above place.  They make them in acetal and brass.

[ChristianJDavis1]

If all else fails, you could try 3D printing new gears.  They might not be as durable, depending on the material used, but you could print enough to be able to replace them for years to come.

To be fair, the original gears weren't too durable, either.

Here's the place I've pointed to for gears a few times.  I bet they have what you need:
https://shop.kkpmo.com/index.php

If you take measurements (diameter, number of teeth, bore, and thickness), you can calculate the module and then
pick out the gear you need from the above place.  They make them in acetal and brass.

I was thinking of a place like that, but I'm missing a few of the measurements. Could I get a measure of the bore by measuring the axle, or would it need to be from the gear itself? Measuring the axle seems easier, but if it isn't the correct way to do it, then it really isn't going to help me.

[garethashenden]

You should be able to measure the axle. If you're using calipers and it comes up with a sensible number you should be good.

[ChristianJDavis1]

You should be able to measure the axle. If you're using calipers and it comes up with a sensible number you should be good.

That's good to know; thank you.

[mmagliaro]

Measuring the axle should be fine.  Yes, the key is coming up with a "reasonable" number.  That shop I linked you to only does
certain bores, so I would hope your gears are something like 1.0mm, 1.5mm, 2.0mm.  The other unknown here is "how tight" a press fit
that gear needs to be on that axle, and how tight the replacement will be.  The tolerances for something like this are really close.   It could go the other way, and instead of being so tight that it stress-cracks over time, it is loose and you get no drive from it.  If the gear that is driving the axle gear is brass, you are kind of stuck with using plastic on the axle gear or you'll get horrible gear wear.  But if the gear driving it is steel or plastic, I think I'd go with a brass axle gear.  At least then, you could slip it on the steel axle with red loctite and know that it will hold if it isn't a tight enough press fit.

[mmagliaro]

I just noticed that at the https://shop.kkpmo.com/index.php site, when you order a gear and select the bore, you can choose the bore fit.
For 1.5mm, for example, you can choose H6 or M6. 

Looking up what the heck that means at this handy dandy calculator site:
https://www.engineersedge.com/calculators/mechanical-tolerances/table_hole_tolerances.htm  ....

A 1.5mm with H6 tolerance ranges from 1.5 to 1.506 mm
With an M6 tolerance, it is 1.492 to 1.498 mm.  I think I would go with the M6 tolerance, since you need these things to fit tight and drive the wheels.  And of course, considering that the cost of these isn't too bad, you could order some of each and see how they fit when you get them.