Tips On Repairing Vintage Diesels

Here are my thoughts and tips on repairing vintage diesel motors.  Take the easiest approach first and carefully work to the most difficult.  It could be as simple as spraying a volume of Radio Shack tuner cleaner on it to clean it, then lube it and test it. Usually, that is all that is necessary. I can't tell you how many times I have smoked a motor and feared the worst. A burnout does happen, but usually it can be saved to run another day - for a while.  So first, lube & clean all motor parts.  You should also check the gearbox. They sometimes have age-old encrusted grease that needs cleaned out and re-lubed with something such as a white lithium grease - or nothing at all but some machine oil. I would not use Vaseline - except as a temporary measure to rule out a gunked-up gearbox. Also oil the pads that lube the shaft. If there is sparking or arcing of the wheels to the frame, it could be from a chassis that needs re-bushed, but hopefully you won't need to go there - although that is a common enough problem in old diesels that have been run to death. Next, you could examine the brushes to see if they need replaced.  Check for any broken wires.  Use a good light to look at the motor and shafts. I have pulled cat hair off of axles by using a pair of forceps with the non-running problem solved as simply as that.  Lastly, try re-centering the commutator in the field by way of the small setscrews on the top of the yoke.  If these things don’t get the disel motor running, then tear it down & rebuild it. If the commutator is shorted out, then it probaly won’t turn at all.  More on that later… 

I can't remember if the commutator is one continuous winding or three separate windings. The field is one winding and when it goes, it goes. At any rate, there should be continuity between all three poles on the commutator. Bob Hannon's repair manual can tell you what the actual resistance value should be. Determining if an armature is shorted is tricky. An armature winding can be worn on one pole so as to have a different resistance than the other two and the motor will still turn, albeit not all that well. As mentioned in the above paragraph, some might say that either the commutator works or it doesn't. That actually is over-simplified reasoning. If one pole is slightly or totally burned out, the motor may still turn - depending on the size of the motor and how well it overcomes friction, but it won't be good. Probably the best way for us home repair guys to determine if an armature is toasted is by the process of elimination. Check everything else and thoroughly service the motor, including checking for worn or broken brush springs, the possibility of a cupped armature face or worn shaft bushings, which would knock the armature out of line a little. If you have done everything and the motor still does not turn - guess what; it’s probably a bad armature. Diesel motors are tougher to get running well than steamer motors, IMHO. When I ran diesels on my layout, I always kept a good spare motor or two to swap out when all else failed. A field can be rewound at home with good results. I never tried to rewind an armature. It’s just too difficult to do at home.

When buying a diesel loco at a train show, turn it over and see how much – if any – lateral wiggle there is on the wheels.  There should be very little or none.  The more wiggle, the more the axel has rounded out the axel hole in the chassis.  That’s not good.  It will result in increased friction on the motor, as the worm gear gets thrust into the motor and/or it will result in sparking between the wheels and frame.  In this case, the best thing for that diesel is: either a drill-out, re-bush of the axel holes or replacement of the whole motor & chassis.  For most home repair guys, a drill-out is not too practical.  It requires a tool-up and skill set jack.  Consider that you will have to pull the insulated wheels off and tap out the axel from the gear and chassis.  Then, after a successful drill-out and pressing in of new bushings – you will have to press the axels back into the gears and insulated wheels.  That can often – very often – be much easier said than done.  More often that not, the wheels will not be true to the axels and they will have a wobble when they turn.  The amount of wobble may be slight or severe.  Either way, it’s not good.  And even if all the above can be accomplished by the average home repair guy, how often would one do it?  Real repairs guys do it often enough to know all the sublties of how to do it right.  Home repair guys don’t.  Bottom line for me is that unless I am willing to stock another inventory of repair parts, tools and jigs and I’m willing to go through all the difficult repair steps necessary on the worst cases – then I’ll just stay away from vintage diesels and only run steam.  The exception would be to buy a diesel in E or E + condition.  They are a little expensive.  However, in the average life span remaining of an old baby-boomer, I probably will not have to do an extensive repair on it.