Mounting motor shaft bushings

[tstage]

Greetings,

I've been working on re-motoring/gearing my Alco Models NYC T-3 that I picked up a few weeks back on eBay.  I have two options:

1. Re-use the existing knurled pulley (from the open frame motor) and track down a replacement spring drive belt for the broken belt that arrived with the model (the other three belts are still good), or...
2. Retrofit the motor shaft and truck axle with sprockets for a chain drive

Background

Locating replacement spring drive belts has been somewhat problematic.  Either I get no response from the vendor...or they won't ship to the US.  NWSL used to offer their 1300-1/TCRT1300 spring drive belts (which is the exact OD and length that I need) but they no longer carry it because, according to NWSL, "we lost our supplier long ago and haven't found another".  I believe I might have found OOP replacements belts from Walthers.  However, both require waiting until they show up on eBay.  I've also purchased the Micro-Mark plastic chain drive with a #3 (10-tooth) sprocket and a NWSL can motor.

The can motor has a 2.0mm shaft.  That requires either a 2.0mm (ID)-to-2.4mm (OD) bushing to use the knurled pulley & spring drive belts...or a 2.0mm (ID)-to-1/8" OD bushing to install the sprocket for the chain drive.

Initially, I'm contemplating going with the spring drive belt option because that requires the least amount of modification to the drive train.  Adding a sprocket to the truck axle requires unsoldering the axle housing and I'm not certain how well the plastic (delrin?) sprocket would hold up under the heat when the time comes to reassemble & resolder the housing.  (If there is thought to the contrary for this concern - I'm all ears.)  I would also need to purchase the smallest (#1) sprocket from Micro-Mark for the truck axle, as the axle housing interior is too small for the #3 sprocket that I purchased.  The #3 should work fine, however, for the motor shaft.

Questions

All the background and the reason for the posting is to pose a few questions about securing the aforementioned bushings to the motor shaft.  Both bushings (purchased from NWSL) slide onto the 2.0mm motor shaft with little-to-no play.  They also press-fit into the knurled pulley and the plastic sprocket with a slight-to-moderate amount of effort.  As a visual, below are photos of each bushing placed on the end of the motor shaft in "exploded" view (double-click to enlarge):

This is the first-time I've used bushings on motor shafts and the NWSL installation instructions are a bit nebulous so here are my questions...

• Q1: Would the bushing for the knurled pulley (top) press-fit into the knurled end of the pulley, with the locking screw securing the pulley hub to the motor shaft?
• Q2a: Same as the knurled pulley except that 1) the bushing would need to be "pinned" to the sprocket (bottom) to lock them together and 2) a locking or set screw would need to be added to the non-sprocket end to secure the sprocket hub to the motor shaft?
• Q2b: Presuming Q2a to be true, would the bushing best be press-fit into the sprocket end because that is where the downward force from the chain would be the greatest?

I think that covers all my questions (so far).  Thanks for taking the time to read and decipher what I'm trying to accomplish.

Tom

[SeeYou190]

Tom, I read your post, and I do not have an answer to your questions.

All I can add is that I used one NWSL bushing once, I think it was 1.5mm ID and 3/32" OD, on a repower project, and it worked perfectly.

That was a long time ago.

-Kevin

[tstage]

Thanks, Kevin.  I just contacted NWSL and asked them their recommendation for each case.  I believe I read somewhere that pinning was required for the plastic sprocket.  That was either on the Micro-Mark website or a PP presentation on brass locomotive upgrades.

Tom

[tstage]

For anyone interested, I received a short reply from NWSL yesterday answering most of my questions:

• The press fit of the bushing into the hubs should be good enough to hold in both scenarios.  For the brass pulley, "only use pinning if you get some undesired spin on [the motor shaft]".  For the plastic sprocket, pinning is not recommended because it "weakens" the hub at that location but any slippage gives you "no choice".
• "If needed", drill and tap a hole in the hub of the plastic sprocket so that a binding screw can lock the sprocket to the motor shaft.  Since the bushing spins freely on the motor shaft, that's what I'll need to do.
• I'm not sure the NWSL tech completely understood my query about the importance of the bushing placement inside the hub.  From my perspective, the bushing should be situated over the point where the spring drive belt or chain will be applying the downward force so that brass pulley or sprocket do not flex.  Perhaps the forces are so low at those locations that any stress on the material are pretty much moot.  I did insert one of the bushing into the plastic sprocket and the only location where it press fits into the hub is at the opposite end of sprocket gear.  If I did desire for the bushing to be located at the sprocket gear end, I would need to pin it.

Right now I'm working on fabricating a bracket (to mount the replacement [can] motor to the chassis) out of K&S 0.064" brass stripping.  I'll need to complete that task first before choosing which drive option to go with...

Tom

[mvlandsw]

Tom,

   I have used those plastic chain sprockets with pinning on the shaft in Hobbytown diesel trucks without any problem. That location is subject to more torque than your use would be. Pressing them on tight enough to avoid slipping might lead to cracking problems with the sprocket. I have seen that on some O scale models that use the chain drive.

   I drilled all the way through the sprocket and motor shaft with a #77 drill bit and used .016' wire for the pin.

Mark Vinski