Need Elec. Motor Guru

[Roberts210]

I'm rebuilding the motor on a Comet Cub. Pulled the rotor out and it's blue, as if it has been overheating.
It is a brushed motor, made to run on 110 VAC, but will also run on DC if needed. I have always run my Comets on 110 VAC.
What would cause this?
I've not used this Comet Cub for many, many years, but I got it out of the rathole to get it up and running.
I need it, so I need to solve this.
I powered it up a few days ago, and I could tell by the sound that it wasn't coming up to full RPM, which, no-load, should be 11,500 rpm. I was guessing it was turning around 7,000.
The end of the motor (opposite the saw blade) felt hot after running it for only a minute or so, and I assumed the bearings were dry, dragging, and bad, but that doesn't seem to be the case.
Any ideas?
If I remember correctly, I had this motor rebuilt some years ago, but then put the saw aside in favor of another Comet Cub. I just sold that Cub, so I need to get this one going. The rebuilder, years ago, put sealed bearings in, and they weren't rated 2Z, but ABEC-1. I have the correct bearings, shielded, rated 2Z, ABEC-3 to go back in, but if the bearings were not the problem I need to find out what is.

 

[Provincial]

First, take the armature to someone that can check thee windings for a short or an open circuit. If the armature windings are good, and if the bearings feel smooth, polish the commutator and inspect the brush contact with the commutator. Get the brushes seated properly, then test again.

 

[Stuart in MN]

I had to look up Comet Cub...is it a radial arm saw? Provincial's suggestions are good.

 

[Roberts210]

Not just a radial arm saw, but the best RAS ever made.

 

[Roberts210]

Thanks Provincial. Will do.

 

[marinusdees]

If it were I, and I wanted to be sure, I'd find an old time motor winder (they're still around, though sorta like dinosaurs) and ask him. He should be willing to offer an opinion for no cost. He should have an armature growler to test the armature, not horribly complex or time consuming. If you have a lathe, chuck the armature up and polish the commutator with some fairly fine abrasive. I'd also measure the brushes and
Google brushes, find some the correct size or close, they can be sanded to fit. You're in it now, so for peace of mind, buy new bearings, they're cheap. Sealed if you have no way to lube them, open if you do and want to. I'd use sealed, that's just me.

 

[Roberts210]

Thanks Marianusdees. I have the correct bearings, shielded, rated 2Z, ABEC-3 to go back in. That's why I pulled the motor apart in the first place--to replace the bearings, but the old bearings seem fine.

 

[Roberts210]

I asked an old motor guy and he told me the bearings that were in there were the type that had been packed with grease to a tighter extent than the precision bearings I got from McMaster Carr. He said to change the bearings and see what happened. I did and the motor runs at full speed again. Score one for the old guys!!! I had also emailed Eurton Electric in Los Angeles (industrial motor rewinders) and they told me the blue color was from a dye that was used.

 

[tym]

Gotta love the old timers.

 

[MShaw]

From having worked for a motor manufacturer our laminations were black like black oxide. The blue is probably the original color of the laminations.

 

[marinusdees]

I asked an old motor guy and he told me the bearings that were in there were the type that had been packed with grease to a tighter extent than the precision bearings I got from McMaster Carr. He said to change the bearings and see what happened. I did and the motor runs at full speed again. Score one for the old guys!!! I had also emailed Eurton Electric in Los Angeles (industrial motor rewinders) and they told me the blue color was from a dye that was used.

I spect the grease in the old bearings got hard. I don't think those new bearings are inferior to the old ones. Hope you live long enough to wear those new bearings out, and enjoy h--- out of that saw.

 

[Roberts210]

I spect you right Massa Marinudees. And I do enjoy the h-e-double hockey-stick out of my Comet saws. Thankee much.