How To Repair 928 Window Motors
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11-15-2008, 02:10 AM
#7
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11-15-2008, 07:34 PM
#11
A little extra to the overhaul procedure to ensure that the job is fully done.
1. Clean the armature and commutator with a good quality electrical solvent to remove dust and grim.
2. The armature core and windings can be painted with a good quality electrical resistant paint to preserve the steel former and the windings from electrical insulation breakdown.
3. The gaps between the commutator segments should be cleaned out to a depth about equal to the gap between the copper segments otherwise a 'short' circuit could result from the entrapped residue of id the copper segments wear down to the insulation, the insulation could become proud and prevent the brushes fulling contacting with the copper segments and electrical 'arking' will occur and eat away the commutator.
The best tool to do this is by using a ground up hacksaw blade. Grind the end of the hacksaw blade down to as small tang around 1/16th of an inch wide and make its thichness the same thickness as the gap between the segments. You can now use this to scrape out the caught up brush material and dust.
4. As the copper of the commutator wears down in way of the brushes, it sometimes necessary to machine the commutator on a lathe to get a flat surface. Once this is done the insulation between the segments need to be undercut. Again a hacksaw blade can be used by grinding off the teeth offset and then giring the blade down to the correct thichness of the gaps between the segments.
5. To finish off the commutator the edges of the segments need to be given a small chamfer. The best tool for this is again a hacksaw blade that has one end ground off square. Insert the right angle into the gap between the segments and draw it to you and you will get a nice 45 degree chamfer on the edge of each segment.
6. If you have to polish the commutator only use a good quality glass paper and ensure that any residue is cleaned out from between the segments.
7. To bed in the brushes, use a good quality fine glass paper. Cut the paper into a strip the width of the commutator and insert it between the brush and the commutator ensuring the back of the glass paper is to the commutator and the glass side under the brush. Hold the glass paper around the commutator and rotate as much as possible until the brush is bedded fully onto the commutator. This will ensure that the full with of the brush is in contact with the commutator segment and it will prevent electrical 'arking'.
You can use this procedure on the starter motor if and when you undertake routine maintenance.
Tails 1990 928S4 Auto.
1. Clean the armature and commutator with a good quality electrical solvent to remove dust and grim.
2. The armature core and windings can be painted with a good quality electrical resistant paint to preserve the steel former and the windings from electrical insulation breakdown.
3. The gaps between the commutator segments should be cleaned out to a depth about equal to the gap between the copper segments otherwise a 'short' circuit could result from the entrapped residue of id the copper segments wear down to the insulation, the insulation could become proud and prevent the brushes fulling contacting with the copper segments and electrical 'arking' will occur and eat away the commutator.
The best tool to do this is by using a ground up hacksaw blade. Grind the end of the hacksaw blade down to as small tang around 1/16th of an inch wide and make its thichness the same thickness as the gap between the segments. You can now use this to scrape out the caught up brush material and dust.
4. As the copper of the commutator wears down in way of the brushes, it sometimes necessary to machine the commutator on a lathe to get a flat surface. Once this is done the insulation between the segments need to be undercut. Again a hacksaw blade can be used by grinding off the teeth offset and then giring the blade down to the correct thichness of the gaps between the segments.
5. To finish off the commutator the edges of the segments need to be given a small chamfer. The best tool for this is again a hacksaw blade that has one end ground off square. Insert the right angle into the gap between the segments and draw it to you and you will get a nice 45 degree chamfer on the edge of each segment.
6. If you have to polish the commutator only use a good quality glass paper and ensure that any residue is cleaned out from between the segments.
7. To bed in the brushes, use a good quality fine glass paper. Cut the paper into a strip the width of the commutator and insert it between the brush and the commutator ensuring the back of the glass paper is to the commutator and the glass side under the brush. Hold the glass paper around the commutator and rotate as much as possible until the brush is bedded fully onto the commutator. This will ensure that the full with of the brush is in contact with the commutator segment and it will prevent electrical 'arking'.
You can use this procedure on the starter motor if and when you undertake routine maintenance.
Tails 1990 928S4 Auto.
11-15-2008, 08:00 PM
#12
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Another couple of window motor problems:
There is a tiny thermal breaker embedded in the nylon end bell. This sometimes corrodes, causing a loss of contact. Quickly found by simple continuity testing. It can be repaired by cleaning the contacts - really tiny, really fiddley work - or by simply bypassing it. If you bypass it, the motor may burn out some day - but if you don't fix it, you just toss the motor now, right?
I have seen a few motors lose contact between the armature windings and the commutator. The little crimped connections on the commutator simply don't make contact any more. This can be repaired by carefully scraping the insulating varnish from the wire right at the commutator crimp, and putting a tiny drop of rosin-core solder on the crimp and wire. If I repair one of these, I normally do every connector on the armature, both to catch any bad connections and to keep the armature in approximate balance.
There is a tiny thermal breaker embedded in the nylon end bell. This sometimes corrodes, causing a loss of contact. Quickly found by simple continuity testing. It can be repaired by cleaning the contacts - really tiny, really fiddley work - or by simply bypassing it. If you bypass it, the motor may burn out some day - but if you don't fix it, you just toss the motor now, right?
I have seen a few motors lose contact between the armature windings and the commutator. The little crimped connections on the commutator simply don't make contact any more. This can be repaired by carefully scraping the insulating varnish from the wire right at the commutator crimp, and putting a tiny drop of rosin-core solder on the crimp and wire. If I repair one of these, I normally do every connector on the armature, both to catch any bad connections and to keep the armature in approximate balance.
11-15-2008, 08:06 PM
#13
Rennlist Member
Usually there no gaps between the commutator segments, they should be insulated from each other. I have repaired several motors using a VW brush holders from spare motors that I have.
