I have a Singer BAK 13-12 motor/light unit which I was intending to fit to my 1953 201K handcranked machine. Just to try it out in use since the 201 runs very sweetly &, being a hand crank, it cannot have been stressed much in previous use.
I did fit the motor but it seemed to have noisy, dry bearings. So I took the motor apart to access the bearings & check the brushes/commutator arm in the process. Unfortunately a wire became detached in that process & I wasn’t sure where it went back… So I looked online for a wiring diagram & could not find one. So I decided to look more closely myself, take some photos & investigate.
All the parts disassembled here. The red wire coming from the coils to the junction box is the detached one. Doesn’t look detached in the pic but it is! The tag is a crimped one rather than soldered & I’m sure now that it should be going there. (My eyesight is poor but looking at close ups makes it all clearer: )
So that seems to solve the wire connection problem. However when I look at the commutator arm & the brushes I discover more potential problems! The commutator arm looks clean & OK at first glance. As pictured I have not cleaned it, it’s just as it was before dismantling. But looking at the close up photos it seems to have some grooves just appearing… One heavier than the other.
Looks to me that the brass brush holder, (or both?) is starting to touch the commutator arm! Worn brushes? When I look at tips of the brushes closely the one on the right is clearly not in full contact with the commutator.
The one on the right is clearly only in contact in a small area on the upper left. The dull lower area is clearly in contact with nothing! The brush on the left has much more contact area, the shiny bit, but the lower half is dull & gradually losing contact also. So my ‘diagnosis’ is that new brushes are needed quickly & that I have discovered this just in time! Any further use will put heavier grooves in the commutator arm… More thought tells me that the brush holders should not be able to move toward the commutator in any case, surely? Only the springs should do that when the carbon wears completely away.
The noises I assumed to be a dry bearing problem were more likely to be this grinding on the commutator arm! Or both. Nevertheless the bearings were dry & will soon be lubricated. The brass cases for the brushes are pictured below.
I’m not sure how long a new pair of brushes should be but they surely should be longer than these? Checking for new ones tells me that many are 11mm long, & these are slightly more than 11mm! Obvious thing to do now is examine closely the ends of the brush holders & sure enough there is a shiny bit on one of them that has been in contact with the commutator arm: ) The problem is not worn brushes it is unfixed holders.
The one on the left is obvious, but I can detect the faint beginnings of another one either side of the split on the right hand one too. But the actual brush holders should not be able to contact the commutator… No matter how the brushes are worn!! It must be the holders were not inserted correctly? They have a lip on the closed end which should limit their movement. If they were inserted incorrectly, with the lip not engaged, by a previous owner, that could explain the problem… I need to reassemble it & make sure the lip is inserted correctly. I took no notice of them when I dismantled it.
So, my final conclusion is that the brush casings were inserted incorrectly before. IE The lip was not engaged with the stop. The brushes are not worn at all, it just needs reassembling correctly.
One small curiosity still lingers however. This brown motor is rated at 75watts. I have another earlier Singer motor with oiling points on the shaft, a black BAK 4-12 which is rated at 0.3AMPS. Which is the most powerful? Innocent me was thinking the 75watt motor was more powerful than the 0.3amp one, but is it? I’m no electrician but I have vague recollections from school (in the 1950s) about V I R expressed in a triangle??
I believe the motorised 201K machines used a 0.3amp motor from the factory & a black motor would suit my black 201 much better than the brown unit (which came from a 185K I think) even though it doesn’t have a lamp with it. I would welcome comments/suggestions on any of the above: )
Success! All together correctly now, plugged it in & it spins quietly & smoothly.