IM Tunnel Motor Shell, Need Chassis

[Mike Madonna]

Good evening,

I have a IM Tunnel Motor (Snoot nose) shell. I'm in search of a suitable chassis to put under it. I believe this topic was once covered in the Summer of 2021 (August). Bringing this back up since it was mentioned that an Atlas SD-50/60 "may" fit under this shell. I have a couple of other complete Tunnel Motors. If someone has a pic (with basic measurements) of an SD-50/60 chassis, I can compare that to the IM chassis. Any input/photos/assistance would be greatly appreciated. Thanks!!

[wmcbride]

I have a recent-release SD50 (Silver with the speaker) that I was going to use under an older Atlas DRGW SD50 shell.

I had not thought about the Intermountain tunnel motors (which I have). If I can dig my tunnel motors out tomorrow (packed from a move), I will give the swap a try and let you know.

[jagged ben]

I'm skeptical the SD50 chassis will fit but the IM Sd45-2 is the same.  Hope that helps.

[Spades]

I believe the truck spacing frame on the sd50/60 is longer than the SD40/45T-2.  SD45-2 frame and truck spacing is less than the SD40/45T-2.  You would probably have to remove/cut/grind the SD50 frames to fit.

[kiwi_bnsf]

Hi Mike,

Interesting question.

The SD45T-2 (like the SD40T-2) has a truck spacing of 45' 2" (whereas the regular SD45-2 has a smaller truck spacing of 43' 6" — the same as the SD40-2 and SD38-2).

The SD50 and SD60 have a slightly larger truck spacing of 45' 10". That 8" translates to 1.27mm extra between trucks in N scale.

That said, from a quick visual inspection of the Atlas SD50/60 mechanism up against the Tunnel Motors, any difference is not noticeable to me, and didn't look to be anything like 1.27mm when measuring with a steel rule, or when making pixel-by-pixel comparison from a photo:

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However, the Atlas SD50/60 mechanism is quite different to the IMRC Tunnel Motor chassis. It is 3mm longer in the nose and it has taller sections above the decoder slot. It looks like there is room to mill away some underframe below the nose of the Tunnel Motor shell, but I have not tried this (others say it is possible for the SD45T-2, but not the SD40T-2). The high points by the decoder would also need filing/milling down).

If required, milling away the front section of the new ESU sound capable Atlas chassis would be problematic as this is where the plastic clips hold the chassis together — you might need to drill a hole somewhere else and screw the frames together (retaining the spacer). Finally, if you are modelling any DRGW Tunnel Motors, then be aware that the Atlas SD50/60 fuel tank section of the chassis would also need milling away as the DRGW fuel tanks are much shorter (and the factory sound might no longer be an option).

I hope this helps.

I'm holding out for a ScaleTrains Tunnel Motor as long as possible, but if they don't come to market in a few years, I might try this chassis swap myself as an easy path to sound (although all my Tunnel motors have already been upgraded with Kato fine scale wheels and a tune up already).

[jagged ben]

Tim, there aren't any differences between the trucks on the new SD50/60 mech as comapred to the older ones, are there?  (Aside from the soldered wire for power, that is.)

[jagged ben]

Sorry I was wrong about the Sd45-2 mech.  Njust checked.  Not the same.

[kiwi_bnsf]

Tim, there aren't any differences between the trucks on the new SD50/60 mech as comapred to the older ones, are there?  (Aside from the soldered wire for power, that is.)

The trucks are unchanged on all the new ESU-capable chassis. Atlas just solder the wires to the old style axle holders.

I have taken to removing the nubs that previously contacted the copper pickup strips as these are no longer necessary. It does improve the look of the trucks to my eye — this Dash 8 truck has had the full treatment with Kato wheels, removed pickup nub, and blackened axle holder on a lowered frame/shell…

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[kiwi_bnsf]

Sorry I was wrong about the Sd45-2 mech.  Njust checked.  Not the same.

All good. I too was initially surprised that the SD45-2 had the same truck centres as the SD40-2. This has led to a personal project to upgrade all my Intermountain SD45-2s to use a modified Kato SD40-2 Mid chassis and under frame. It is a lot of work, but worth it IMHO — the locos have a lot more heft when the gap between the shell and the trucks is filled with under frame detail…

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(This was my first production conversion for @Doug W who models Clinchfield)

I have posted a separate SD45-2 conversion how-to here…

https://www.therailwire.net/forum/index.php?topic=55139.msg756592#msg756592


Sorry for the thread drift!

Cheers