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Diesel Locomotive Wheelbase?

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  • Member since
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Diesel Locomotive Wheelbase?
Posted by RR_Mel on Sunday, August 2, 2020 8:10 PM

Diesel Locomotive Wheelbase

I’ve been piddling with a few locomotives and went to Wikipedia to compare the wheelbase of an SD40-2 and a EMD E8 and something doesn’t add up.

I have several HO Athearn SD40-2s and several E7s from Proto and Model Power.  I used them as go bys and the model to actual scale is less than a foot difference truck bolster to truck bolster.

Wikipedia states “43’ 6” between truck bolsters” for the SD40-2 but “57’ 1” wheelbase” for the E7.

I have been using Bowser (Cary) E7 shells for my E7 fleet for years, Bowser recommends the Athearn SD40-2 frame for their E7 body.

Today I was finishing up a special E8 (video camera locomotive,SQ8 camera) using the SD40-2 frame and using a Proto 2K E8 shell when I decided to check the dimensions when I ran into the discrepancy in wheelbase.

I went to a model railroad site and it to listed 57’ for the E series locomotives.

I’m not a mechanical engineer so could someone explain the difference to an electronics guy.

By the way the SQ8 camera fits nicely in side the Proto E8 shell, I chopped off the front of the Athearn SD40-2 frame and kitbashed a camera mount.

I still need to do some finish work on the old Proto 2K shell, its been in the bottom of my shell bin for years.



Mel



 
My Model Railroad  
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Bakersfield, California
 
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Posted by gmpullman on Sunday, August 2, 2020 8:23 PM

Hi Mel,

From what you describe, as I understand it, the "Wheelbase" would be the distance from the first pair of wheels all the way back to the last pair of wheels on the second truck, meaning you would need a length of rail 57 feet, one inch long to place the locomotive.

The bolster centers are measured from the center of each truck and would be reduced by the "wheelbase" of one truck (half the front truck and half the rear truck).

As an example, this E7 diagram shows a wheelbase of 57' - 1" and bolster centers of 43' - 0". Therefore each truck has a wheelbase of 14 feet, 1 inch, half of which projects forward and rearward from each bolster center exactly 7' - ½".

 NYC_DPA-E7 by Edmund, on Flickr

To complicate matters, not all locomotive trucks have the bolster centered on the wheelbase. The Alco C-630 comes to mind, also the SD40-2 has an offset of 1-¼" from the center axle to the bolster pin:

 EMD_SD40-2_diagram by Edmund, on Flickr

Hope I didn't complicate matters even more.

Good Luck, Ed

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Posted by RR_Mel on Sunday, August 2, 2020 8:46 PM

Thanks Ed.

The Proto is right on the money, lead axle to trailing axle is 57’ 2” at 7 5/8”.  The Athearn SD40-2 is also very close to 43’ 6” at 5 15/16”.

I guess Wikipedia just doesn’t have their stuff together.


Mel


 
My Model Railroad  
http://melvineperry.blogspot.com/
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 

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  • From: Reading, PA
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Posted by rrinker on Sunday, August 2, 2020 9:43 PM

Doesn't help that this guy also confuses it, saying the truck centers are 57'. That's just not right.

https://www.thedieselshop.us/Data%20EMD%20E8.HTML

                                           --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by Overmod on Monday, August 3, 2020 6:34 AM

The situation might be complicated if the truck wheelbase is wrong, as sometimes happens on models where it's cheaper to jigger cheap molded or coined sideframes than expensive geared mechanisms from a prototype with marginally-different axle spacing... or if the truck on the model is mounted essentially 'bolsterless' or 'centerless' in the frame to facilitate truck rotation and 'artiulation' to line and cross-level and is not precisely where a bolster pin (or pads, etc.) would locate it on the prototype.

As indicated you need to know both the bolster-center dimension and the truck wheelbase and any centerpin offset to get the physical wheelbase if you cannot measure it directly.  

No one has yet brought up the issue that the wheelbase measurement can be 'prototypically correct' but at a very wrong offset longitudinally relative to the coupler pulling faces... likely as important to a rivet-counter as getting the wheelbase or truck-center distances 'word-perfect'...

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Posted by RR_Mel on Monday, August 3, 2020 9:56 AM

rrinker

Doesn't help that this guy also confuses it, saying the truck centers are 57'. That's just not right.

https://www.thedieselshop.us/Data%20EMD%20E8.HTML

                                           --Randy

 

 

Randy

It was that site that caused me the problem and the reason for this post.


Mel


 
My Model Railroad  
http://melvineperry.blogspot.com/
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 

 

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