There are many cases where older motors do not perform very well, but replacement with newer types is not too practical without major surgery and drive train alterations. To test the possibilities of improving these older motors, newer magnets were installed with improved materials that have drastically increased the field strength. Having many spare DC-60's on hand and finally locating some possible replacements, a trial was made.
First tests were run with the original. Then the magnets were exchanged, followed by tests for comparison.
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Original Pittman DC-60.
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DC-60 With new magnet, mounted on Penn-Line PRR H9s frame.
CAUTION: Do all worm pressing before exchanging magnets while the motor is in the original more rigid state. Since the rear screw, which holds the frame in alignment, will not be used; pressing gears on shaft can distort pole pieces and front bell alignment. I learned the hard way and had to line things up by ear. Applying some ACC to the pole piece to bell joint beforehand can prevent bell rotation and movement.
Check the polarity of both magnets to assure the same orientation in the motor. Simply remove rear screw and magnet, which will now lose most of its field strength. This is not the case with the new magnet. In some cases, burrs, left from drilling a tapping or stamping pole pieces, force the bell ends together by leverage. This can throw bell out of alignment, causing binding. File the pole piece magnet contact surface lightly to remove. Place the new magnet in the opening. It will probably snap in, pulled by the magnetic force. Line it up with the sides. The rear end will extend past pole pieces; but, except in tight cases, causes no problem except a slight loss in flux path. Alternatively a hole my be drilled with a wet diamond bit to clear rear bearing and place magnet against the upright. In most cases the magnetic force will hold it in place, but for security a few drops of ACC around the edges and down the screw holes will help. Tests were run without cement with no problems. Just mount and test.
The speed of these motors varies over the years and with the Bowser versions. The one used ran light at just under 16 k RPM, while it dropped to close to 10 k with the new magnet. This may be attributed to the expected increased torque. Current dropped from about .2 amp to about .11 amp. Stall torque and other measurements are compared in STALL TORQUE DATA ,
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