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Hi,

I have a 1990's era Overland model 6-axle diesel and I have an issue with the Pittman motor, model 8413-B668 12 Volt built 5/29/90.  The motor runs okay at the slower speeds but as the voltage increases beyond the half way mark, the motor actually decreases in speed.  Basically, it runs the same or slightly faster at half voltage than at full voltage.  The motor also begins to get quite warm, but never to the point where it is too hot to keep you fingers on it.  Therefore  I would like recommendations on the following:

  • Does anyone have a recommendation for a current Pittman or other manufacturer replacement motor?  The existing motor is 30 mm wide x 55 mm long.  The shaft diameter is 4 mm.
  • Do I salvage the flywheels (are they just attached to the motor shafts with CA or press fit as I do not see any set screws) or do I just turn some new ones?  If they are CAed to the motor shaft, then could they come off with some heat from a micro torch?
  • How are the universal joints on each of the flywheels attached; are they glued to the flywheel or are they press fit in the counter-bore at each end of the flywheel?

 

Thanks so much!.

Scott Kay

Austin, TX

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  • SJK_0283: Overland  Drive w/ Pittman Motor
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I would replace the motor with a new Pittman with the latest magnet.  In the past, I have purchased as little as one motor at a time.  They were very easy to work with.  Google them and give them a call.  They are located in PA.  BTW, the 8 indicates the diameter, the 4 indicates the location of the contacts on the outside of the motor, the 1 indicates the type of magnet (they are up to 3  now) and the 3 indicates the length of the motor.  Altogether, you have model #8413.  You would want a model #8433.

I can't help with the rest of the issues.

Best of luck,

Ed

 

You can get replacement 8413 motors all day long.  P&D has a box of them on his table right now at the Chicago meet. Or from eBay.

The newer versions do have better magnets.  But a straight up replacement would be easy to find.

For CA my understanding is that you would freeze it rather than heat it.  I think it makes the bond brittle so it can be broken easily.

 

Beyond that somebody else will need to provide answers.

Hi Scott,

Lou Houlemard (email- clwusa@verizon.net)of Central Locomotive Works, Bill Davis of American O Scale, and a guy who goes by the name of motorman might be able to get you a direct replacement of the same length to fit the OMI motor mounts.

Motorman(email- motorman@micro-loco-motion.com) might be able to find you a replacement in a Faulhaber or Maxon that might fit the specs you need without modifications.

I have a few of the early 90's OMI units and the flywheels on two of them are press fit as I was able to turn them to align u-joints on drive shafts. They were really tight but didn't appear to be glued on. So you should be able to salvage the flywheels if necessary.

The u-joints on each flywheel were only press fit. I just replaced one on an 8-40BW and removal with needle nose pliers was pretty simple.

Travis

It should be easy to replace the motor if you go with the same physical size (8xxx series diameter, x4xx brush location, xxx3 length).  I strongly agree with Ed Kelly's recommendation to go with a rare earth magnet motor.  Their far higher starting torque provides smoother low speed control - especially noticeable when starting a heavy train on a grade.  Over a 25 year span I've re-motored all my OMI steam and diesel locomotives.  I haven't had a failed motor, but did it to improve performance.

Last edited by Keystoned Ed

Thanks so much guys.  You guys are rock stars .  I looked over the Pittman web site and I found this 8541 motor below was basically an exact dimensional match, including the shaft diameter and mounting holes, to my current 8413 motor.  I found some electronics and automation supply houses list this motor for around $125 ea. but none show it currently in stock so I am just going to call Pittman on Monday and see if I can order one direct from them.   I will keep everyone posted on the progress of this motor repair job. 

http://www.pittman-motors.com/...rs/8540_dc_motor.pdf

Thanks again.

Scott Kay

Austin, TX

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