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Old 06-18-2017, 02:27 PM   #1 (permalink)
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Default 40 inch wheel conversion

I guess I could have stuck this subject in with the GP9's I'm rebuilding, but as these wheels are being used on the GP30's the S4 as well as the GP9's I thought it might be better to start a new post.
So, the wheels were purchased from NorthWest Short Lines though OSORAIL.com and are item #2522-6 Large Scale (1:29) 40"/236 NS wheels, which come in a quantity of 8 for $36.95 plus shipping and handling. These are replacements for the standard USA Trains wheels used on their diesel engines.
On this latest batch I purchased I found the axle projected beyond wheel face by 0.028" This was corrected by a slight tap on the back side of the wheel with the wheel resting on a flat face and the axle stub extension located in a hole drilled on the flat surface. I guess I could have done the same in the vice.
Also in this batch I found the axle stub which fits into the USAT journal box to be slightly oversized up to 0.118" instead of 0.115" I realise this is only 0.003" difference, but it has the potential of restricting flexibility on curves and switched. So I machined these down to 0.115"
This is one of the wheels as received and it shows the axle projection through the wheel.

To accommodate the larger wheel which is 1.370" diameter vs the USAT wheel at 1.120" it is necessary to move the brake shoes out of the way to allow for the new wheels to fit. This was done with a razor saw. It's necessary to remove the journal box to provide access for this and when this is done and the saw cuts cleaned up the journal boxes can be reinstalled to permit brake shoe locating prior to gluing the shoes back in their new location.

I use a 1/8" square styrene rod to space the shoes apart.

This picture shows some assembly stages.

It's important to note that one end of the motor block causes interference with the wheels and needs the have some clearance cut into the motor block moulding. This can be seen on the right wheel.


Last edited by harvey; 06-18-2017 at 05:08 PM.
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Old 06-18-2017, 03:39 PM   #2 (permalink)
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Nice technique on re-using the brake shoes. Many people just grind them away for clearance, and it looks terrible.

Thanks for the information!

Greg 1,130
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Old 06-18-2017, 04:49 PM   #3 (permalink)
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Hi Greg, I got interrupted while doing this post so here's the rest of it.

This is an upside-down view.

This is a comparison between standard supplied USAT truck and the modified version with the larger wheels.

I think this pictures fits in the category of more is better!

I took the bottom plate off to show where I added an outboard washer. This is a 1/4" x 0.040" brass washer and although it restricts the sideways movement to only 0.040" in total it has the benefit of keeping the gears aligned.

For further information the B-B of the USAT is 1.560" and the NWSL is now 1.580"
Wheels on USAT trucks are 1.120" and NWSL 1.370. What I've done on engines that have been retrofitted is to add a 0.125" shim under the Kadee coupler to bring it lower.
Hope this will help others who might be contemplating an upgrade on their diesel engine trucks.

Last edited by harvey; 06-18-2017 at 05:12 PM.
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Old 06-19-2017, 09:03 PM   #4 (permalink)
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Looks good Harvey, great work.
If in doubt, slab out!
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Old 06-20-2017, 10:50 AM   #5 (permalink)
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Thanks for the info!
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