Replacing electric motor brushes

[os1kne]

I have a very old Black & Decker 987 circular saw that was inherited from my FIL. Not sure how old it is, but I'd guess 40 years or so. It's a pretty nice CS; it's very heavy and has a nice flat steel base. It's my "go to" saw for ripping down sheets of plywood, etc.

Anyway, I was using it recently and the motor started behaving erratically - identical symptoms to what I've read for worn out brushes. The brushes appear to be easy to replace - I just haven't been able to find what size to get for the saw. Do brushes change dimensions with age/use? or can I simply measure the existing brushes to order replacements?

Also, while I'm at it - do you know if the service centers carry replacement parts for tools this old? The blade guard also doesn't work as it should, seems that I need a spring and another part - I've been working around this for a few years, may as well get it tip-top.

Thanks for your help - I'd like to keep the old saw going.

[Pappy]

The width and thickness of the brushes should be all you need, but a good repair shop may be able to look the part number up off the model #.

I have an old B&D that needs a return spring on the guard as well. Since I have 3 CS, I haven't really looked for one.

[cabinetman]

I have a very old Black & Decker 987 circular saw that was inherited from my FIL. Not sure how old it is, but I'd guess 40 years or so. It's a pretty nice CS; it's very heavy and has a nice flat steel base. It's my "go to" saw for ripping down sheets of plywood, etc.

Anyway, I was using it recently and the motor started behaving erratically - identical symptoms to what I've read for worn out brushes. The brushes appear to be easy to replace - I just haven't been able to find what size to get for the saw. Do brushes change dimensions with age/use? or can I simply measure the existing brushes to order replacements?

Also, while I'm at it - do you know if the service centers carry replacement parts for tools this old? The blade guard also doesn't work as it should, seems that I need a spring and another part - I've been working around this for a few years, may as well get it tip-top.

Thanks for your help - I'd like to keep the old saw going.

Used/worn brushes will be scooped out, and shorter than original. A parts supplier should be able to get the exact parts or an equivalent. B&D circular saws are popular, and parts for the guard should also be available. Skil may have equivalents.

.

[cork58]

I've dealt with these folks a few times, if you know the model I'd give them a try.

http://www.ereplacementparts.com/bla...4167_4252.html

[mpc]

Electric motor "brushes" typically start out as rectangular bars of soft material; one end is then filed to a "C" shape to make smooth contact with the armature. The "backside" of the brush usually has a spring attached to it, or at least a bump/shape to keep one end of a spring in place. And typically it'll have a flexible braided electrical wire "tail." The bar gets shorter and shorter with age until a) the wire is stretched as far as it'll go so the spring can no longer push the brush into the motor, or b) the brush is so short that the fully extended spring isn't enough to push it into the motor.

The cross sectional size of the brush is the main item to watch for when looking for replacements. Ace Hardware and some other hardware places have plastic bins full of various sized brushes, just take one of the old ones in and match up the cross sectional area along with the spring/spring attach shape & minimum wire length. Ideally the new brush will have a "C" shaped end; if not you can carefully file it. You may have to solder the wire tail to the saw or it may just pinch in place or get held by a screw. And you may have to cut an over-long brush to length. To guesstimate the length, you want the spring almost but not quite fully compressed when the unit is assembled.

Re-assembling some motors after brush replacement can be a pain. If the saw has screw-cap openings for the brushes it'll be a LOT easier. Otherwise you have to:
a) hold both brushes deep in their guides while...
b) pushing the motor armature between the brushes. Except there's usually no room for fingers or skinny screwdrivers. Look for small holes in the brush holders: use unfolded paper-clips through the holes to trap the ends of the new brushes inside the holders. These holes may dictate how long the fresh/new brush can be too!

mpc

[woodturner]

Ideally the new brush will have a "C" shaped end; if not you can carefully file it.

Great information on brushes and replacement and very helpful. Just wanted to add, though, that in my experience, brushes usually come with a square end, and it is not necessary to file them to a "C" shape. The square end will quickly wear to the shape of the commutator and will be a perfect fit. Even if the brushes are filed to a "C" shape they will not fit perfectly and will have to wear in.

Good sources for brushes are electric motor repair shops, alternator repair shops, "old time" hardware stores, and electric supply houses that cater to the trade.

[Mr__Bill]

I have had good luck with off the shelf brushes from my local ACE hardware store. I just match the old ones to the new, the new being much longer.


Bill
on the left coast

[Tom Slick]

According to the Black and Decker website you have at lease three service centers in the Atlanta area:

Factory Service Center #111
6115 Jimmy Carter Blvd Ste C
Norcross, GA 30071
770-246-1710

Power Tool Service
1420 Collier Rd N.W.
Atlanta, GA 30318
404-605-0101

Als Air Compressor Service
2548 Lantrac Court
Decatur, GA 30035
770-922-1273