Induction motor repair

[PaulO]

The Brook Crompton 0.5hp motor on my Fobco drill seems to be a bit louder than it used to. Applying slight downward pressure on the spindle seems to stop the noise/vibration. I'm guessing this means that one/both of the bearings is shot. Does anyone know if changing these is a home workshop job, or should I take it to a specialist motor repair shop?

 

[Digit]

DIY if you have the necessary spanners etc. You might need a puller to remove the bearings, or if you're very good, and desperate, a disc grinder will shift 'em.

Roy.

 

[9fingers]

Paul, Motor bearing changes are relatively simple if you are comfortable with mechanics and have a few tools such as a puller- not always needed but sometimes.

Firstly mark the two end caps and the central body with a centre punch or knife scratches to ensure you re-assemble with all parts in line.

Remove the bolts holding the ends on. usually through rods with nuts on each end. Don't try a prise off the ends but tap the end of the shaft, square on with a RUBBER mallet not a hammer untill the rear cap starts coming off.

Inside you will see the centrifgual switch. observe what goes where and perhaps by removing the electrical connection terminals, remove the rear end completely. The bearing may stay on the shaft or stay in the rear end cap.

Apply the rubber mallet trick to the rear end of the shaft to remove the front end cap. No wiring to worry about here. Brin the rotor out via the front to avoid catching the wiring.


Remove the bearings and look for the numbers like 6003 or 6004 maybe with z or zz or RS or 2RS suffixes. these are standard sizes for metric bearings and the suffixes say what sort and how many shields are fitted.

2RS (2 x rubber shields) are the most sealed and at motor speeds add very little friction. If you can't find the numbers make accurate measurements of the width, bore and outside diameter and I'll look them up for you.
Lots of bearings available on line from Ebay or ArcEurotrade quite cheaply to name but two sources.

Fit the new bearings onto the rotor using offcuts of tube to apply pressure on the inner bore with the rubber mallet. Do NOT hit the outer ring of the bearing.

Offer up the front end cap to the rotor and seat the bearing as far as it will go. Reassemble the centrifugal switch and offer up the rear end cap and seat the bearing.

Align the telltale marks you made at the begining and loosely fit the rods and nuts. tighten each nut in turn so the the end caps are pulled on squarely to the motor body.

Check to see if the rotor spins as freely as before allowing for the slight drag of the centrifugal switch. If the rotor is not free, then just loosen the nuts 1/4 turn and hit the shaft with the mallet along the axis of the shaft.
and re tighten the nuts. this should finally seat the bearings. Sound a bit brutal but it usually does the trick.

Job Done.

Come back if you need more help

HTH

Bob

 

[PaulO]

Thanks for the advice,
my main concern was that in removing the end cap, there would be a ping and the centifugal switch would be distributed about my workshop in individual pieces. Just like when I tried to dissasemble the aperture mechanism of a camera lens when I was 10! Still that wasn't quite as dissapointing as when my uncle (aged 12) decided to take a look in his dad's Rolex oyster, removing the back of the case using a cold chisel and mallet.

Are the bearings the prime suspect for an increase in noise, as I did read that it can be caused by loose frames / shields being excited by the rotating field?


I'll give it a go tomorrow.

 

[9fingers]

Paul,
The trick with the centrifugal switch is to stop just as the cap is released so you can see what goes where. It is not normal for parts to come flying out.


It is just possible that a metal shield is loose and resonating due to the field but if the bearing it self is that loose/short on lubrication then it is time to change it anyway.

Good Luck

Bob

 

[Digit]

And either way the motor's got to come apart for you to find out.

Roy.

 

[PaulO]

Thanks for your help, 2 off 6203-2rs bearings replaced, and the motor now runs much quieter. Only thing is, now it has me thinking about the bearings on the quill side of the drill. But given that 95% of its duty is in wood, and I have measured the runout to be less than 1 thou TIR, I'm not sure it is worth the bother.

 

[9fingers]

Good Result then and no trauma!

Thanks for letting us know.


Bob