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Discussion Starter #1
It might take you electrical engineers to answer this question:

Why do speeds often vary between identical locomotive motors? Surely the gear sets are the same. If each motor armature has the same number of windings, if the magnets are made from the same batch of metal, if the motors are subjected to the same voltage at the same time (placed on the same track), why will one loco invariably run a bit faster or slower than it's identical counterpart?
 

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Many reasons.
Magnets weaker
Air gap different
Bearings tighter
To name a few...
 

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Do you mean same locos on track, not identical speed ? Or do you mean the motors themselves (as if you removed them from the loco) ?
I'm guessing you mean the first one. In that case you just got to blame the physics. Our miniature trains are not riding on Timken roller bearings. And the tiny motors can not be made to exacting specs like a NASA rocket...There's friction involved and even dirt and dust which come between the pickup wheel tire treads and the rail head..M
 

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Discussion Starter #5
I don't know, guys. If the magnets are made from the same batch of metal, why would one be weaker than another? Why would air gaps fluctuate?...The bearings would determine that. Maybe I'm naive, but surely the big-name manufacturers (Kato, MTH, BLI, Athern, etc) have standard tolerances. For what they charge for those things, there OUGHT to be standards! Assembly should be pretty standard person to person...parts made within good standards fit together, period. And as I said, good-name manufacturers would insist on quality control. I do understand the smallness of things and we're running most likely on brass bearings, but sometimes the speed differences are significant!

As I said, maybe I'm assuming too much. I'm just wondering why things are different. And maybe your ideas are truly the causes...I don't know.
 

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I purchased two used Proto 2000 GP7s at different times from different sellers. No clue when they were made, but they are identical. The one that showed some use ran much better/faster then the one that appeared to have never been out of the box. I cleaned and re-lubed all the "workings" and they now run so close that I double-head them... which was my intention to begin with.

Same story with two new, new stock Bachmann GP9s that I purchased at the same time from the same place. The speed variance wasn't as bad as the GP7s, but one would steadily pull away from the other. Cleaned and re-lubed (yep, brand new locos) and they are now "speed matched".

I know that's only two data points (or is it four?), but that's my experience.
 

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I don't know, guys. If the magnets are made from the same batch of metal, why would one be weaker than another? Why would air gaps fluctuate?...The bearings would determine that. Maybe I'm naive, but surely the big-name manufacturers (Kato, MTH, BLI, Athern, etc) have standard tolerances. For what they charge for those things, there OUGHT to be standards! Assembly should be pretty standard person to person...parts made within good standards fit together, period. And as I said, good-name manufacturers would insist on quality control. I do understand the smallness of things and we're running most likely on brass bearings, but sometimes the speed differences are significant!

As I said, maybe I'm assuming too much. I'm just wondering why things are different. And maybe your ideas are truly the causes...I don't know.
Because the parts intended for model railroad use are not intended for precision engineering application (rocketry, fine scale manufacturing, etc), so some slop in the tolerances and standards is acceptable, and adding precision adds cost. They're manufactured to "close enough for hobby use" standards. It's also a huge leap that every part of every component on two otherwise identical locos all came from the same batches of parts.
 
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