Motor

Last Updated: 1 September 2008

The original motor for this machine is a squirrel-cage induction polyphase type made by Century Electric Company from St. Louis, MO.  Century doesn't exist as an independent any longer, having been bought out by A.O. Smith some time ago.

Specifications listed on the motor plate are as follows (laid out roughly as they appear on the plate):
Code K
Model SC-203-N Spec No. 13102
H.P. 1 Phase 3 RPM 1740/1450
Cycle 60/50 Volts 220/440 Amps 3.8/1.8 - 4.6/2.3
Time Rating: Continuous Open Temp Rise 40°C
Service Factor 1.25 Serial No. AG1

The bottom of the plate reads "This motor will operate successfully on 208 volts".

This motor is in remarkable mechanical condition considering its age.  Other than a light coating of rubber particles (from the vee-belts), it's relatively clean and free of any grease or oil.  The bearings are whisper-quiet and smooth, but I do intend to add some grease to them (ball bearings) to keep them happy.  I spoke with a local electric motor repair shop, M&R Electric, and they provided me (free of charge!) some old-timey grease that will be compatible with any existing grease still in the bearings.  [Modern bearing grease for electric motors is Polyrex EM, but it's never a good idea to mix grease formulations].

Re-greasing the bearings won't be easy without removing the end bells from the motor, since there's no direct shot to the bearing housings.  But I'll do my best to force a bit in there.  I will not be using a grease gun, as excessive grease pressure can damage the bearings, so why take a chance?

I was able to obtain a series of brochures from Century published between 1920 and 1950 from the Smithsonian (which was the only library that had copies).  The good folks at Smithsonian were kind enough to provide copies of the documents through inter-library loan at no charge.  If anyone else out there would like a copy, email me.  Here's a list of the documents I got:

1. Squirrel Cage Induction Polyphase Motors (1943)
2. Repulsion-Start Induction Single Phase Motors (no date)
3. Totally Enclosed Fan Cooled Multi-Speed Motors (one page, no date)
4. Squirrel Cage Induction Polyphase Motors (1928)
5. 'Invincible' Split Phase Motors (estimated 1922)
6. Squirrel Cage Induction Polyphase Motor Assembly (no date)
7. How Century Polyphase Motors are Built (no date)
8. Century Polyphase Motors 1/2 to 60 Horsepower; Automatic Start; Induction Type (no date)
9. Polyphase Motors Stator and Field Winding Assembly (no date)

Century's slogan, at least during this time period, was "They Keep a-Running".  The literature abounds with rhetoric about how long lasting (indeed, "invincible") these motors are.  They sure are substantially built - that little 1 hp weighs about 40 lb.

The motor is heavy, but can be removed solo if you stack at least ~2.75" of blocks beneath it before removing the 4 3/8-16 screws that secure it to the motor plate.  The motor plate, however, is easier to remove and install if you use either 2 people or a floor jack, as shown in the first photo here.  The key is to get the hinge pin out while keeping the motor plate level, thereby preventing the pin binding.

The second photo shows the motor mount plate removed.  This is a simple piece, made from solid cast iron roughly 1/2" thick - which means it's remarkably heavy.

The third photo shows rear end bell on the motor with the oil (or grease) fill plug notated.  That fill plug, and the corresponding one on the front, gave me fits trying to figure out what should go in there.  This is a ball bearing motor, which suggests it should be greased, but there's no drain plug for cleaning out the old grease.  After a great deal of debate and discussion with various motor shops I finally decided to use the old timey grease I mentioned earlier, along with a couple tiny drops of Mobilgear 629 gear lube for good measure.  I added very little grease.  I suspect this motor has never been regreased, as I could find no evidence whatsoever that any grease had ever been pumped into the bearing housings - they were extremely clean inside.








As you can see in the first photo on this page, the motor has a diagram indicating how to wire it for 220 or 440 volts.  I was a bit concerned by the diagram, because it suggests (to me, anyway) that there was originally some sort of 9-pin circular connector that was installed and subsequently cut out in favor of electrical tape (the lazy electricians best friend and the bane of good electrical engineers everywhere!).

I was tremendously pleased, then, when I removed the electrical tape to find the wires all have crimped lugs with the wire number stamped into each lug.  (You can't see these stampings in the photo).

The electrical tape will be replaced by self-fusing silicone tape, because I hate electrical tape.  The wires coming in from the power supply were merely curled and sandwiched between the lugs for each phase.  I will eliminate those and use crimped and soldered replacement lugs for 10 ga. wire.