NateA2
Cast Iron
- Joined
- Sep 4, 2012
- Location
- Ann Arbor MI.
Morning all!
I wanted to jot down my recent experience so that if someone else needs to pull/rebearing/rebrush their MG unit, they can read this to get a feel for the process I used.
Remove power to lathe. Actually remove the connection, not just disconnecting via fused disconnect etc.
Remove rear cover, front cover and MG end cover.
Open junction box behind front cover.
Photograph all connections in junction box and all motor wires, brushes, etc before removal.
Label any wires that are ambiguous, cannot be read, are unlabeled etc.
Disconnect wiring coming into junction box.
Remove motor mount bolts.
Wedge pry bar under motor feet and lift off rubber bushing. My motor feet were stuck to the rubber bushing, which was in turn stuck to the lathe body.
Pull MG unit out of lathe. Note- weight is estimated at 200 lbs. caution.
Remove PiggyBack Exciter. note height and turns of coupling bolts. Write this down. I wish I had. Resetting the PBE unit is a pain in the ass.
Wires on PBE may be brittle. Use caution.
Remove MG fan cover.
Remove MG brush side outer bearing cap. Note location and orientation. Inner cap is now loose. caution not to hit commutator etc. use caution when hand spinning MG shaft. do not ding commutator.
Remove brush side mounting foot casting (front two legs of MG unit.)
Note brush locations, pull them and mark them with locations.
Set aside the brush pushers, gently move them to a place where they will not hit commutator surface etc. note: fragile parts. use caution.
Exercise caution to not bump or nudge brush holders out of alignment/timing.
Remove MG fan. This was simple, as shaft was straight not tapered.
Remove MG fan side bearing retainer. note location and fact that rear bearing cap will now be loose.
Remove fan side MG end casting.
Gently slide out MG shaft. Use caution. its heavy and you don't want to damage, bend or nick anything on this part.
Photograph and measure bearing locations from shaft ends or other datum.
Check bearings for free spinning inner race (inner race to shaft fit)
Check outer races for evidence of a "spun bearing"
Remove bearings. do not use bearing retaining caps as pullers. Use a real puller. I had to fab one from tube for the brush Side. I used a close fitting tube and put a nut on one end with a threaded shaft. welded the puller tube directly to the outer race of the bearing and extracted.
Do not use the bearing retainer caps as pullers. especially the brush side, as their is a small retaining ring behind the bearing.
Do above steps on PBE unit.
Clean everything gently. check for bad insulation on any visible wires on PBE and MG. Correct as necessary.
Do not move the brush holders on either the PBE or the MG. clean them with plastic brush
Inspect commutator surface.
put bearings on MG shaft. They must be in the same locations as before. set as close as possible to original.
Reinsert MG shaft into MG casing. Use extreme caution. heavy and unwieldy.
Reaffix all bearing caps etc.
Reaffix all end covers, fan, etc.
Machine new brushes on milling machine for close approximation of commutator surface. Boring head is ideal for this task.
Check brush fit. if tight, slightly stone brushes until fit is correct.
Reaffix brush retaining springs/pushers. set correct tension.
Refit PBE unit to MG body.
Refit Pulleys.
Hand rotate MG and PBE units and apply commutator dressing stone to commutator surfaces in front of brushes. rotate as per correct rotation. Check brush face fit to commutator surfaces. correct as needed. Brushes are very fragile, use caution.
Once correct fit is established, fit pushers and set tension.
Reconnect everything.
gently brush out all commutator stone dust.
Hand rotate to check for binding etc.
Rewire.
Reconnect Power.
Test MG/PBE for functionality.
Run for 30 Seconds, cool down, run for 2 minutes, cool, run for 5 minutes, cool, run for 30 minutes cool.
Refit machine covers.
I wanted to jot down my recent experience so that if someone else needs to pull/rebearing/rebrush their MG unit, they can read this to get a feel for the process I used.
Remove power to lathe. Actually remove the connection, not just disconnecting via fused disconnect etc.
Remove rear cover, front cover and MG end cover.
Open junction box behind front cover.
Photograph all connections in junction box and all motor wires, brushes, etc before removal.
Label any wires that are ambiguous, cannot be read, are unlabeled etc.
Disconnect wiring coming into junction box.
Remove motor mount bolts.
Wedge pry bar under motor feet and lift off rubber bushing. My motor feet were stuck to the rubber bushing, which was in turn stuck to the lathe body.
Pull MG unit out of lathe. Note- weight is estimated at 200 lbs. caution.
Remove PiggyBack Exciter. note height and turns of coupling bolts. Write this down. I wish I had. Resetting the PBE unit is a pain in the ass.
Wires on PBE may be brittle. Use caution.
Remove MG fan cover.
Remove MG brush side outer bearing cap. Note location and orientation. Inner cap is now loose. caution not to hit commutator etc. use caution when hand spinning MG shaft. do not ding commutator.
Remove brush side mounting foot casting (front two legs of MG unit.)
Note brush locations, pull them and mark them with locations.
Set aside the brush pushers, gently move them to a place where they will not hit commutator surface etc. note: fragile parts. use caution.
Exercise caution to not bump or nudge brush holders out of alignment/timing.
Remove MG fan. This was simple, as shaft was straight not tapered.
Remove MG fan side bearing retainer. note location and fact that rear bearing cap will now be loose.
Remove fan side MG end casting.
Gently slide out MG shaft. Use caution. its heavy and you don't want to damage, bend or nick anything on this part.
Photograph and measure bearing locations from shaft ends or other datum.
Check bearings for free spinning inner race (inner race to shaft fit)
Check outer races for evidence of a "spun bearing"
Remove bearings. do not use bearing retaining caps as pullers. Use a real puller. I had to fab one from tube for the brush Side. I used a close fitting tube and put a nut on one end with a threaded shaft. welded the puller tube directly to the outer race of the bearing and extracted.
Do not use the bearing retainer caps as pullers. especially the brush side, as their is a small retaining ring behind the bearing.
Do above steps on PBE unit.
Clean everything gently. check for bad insulation on any visible wires on PBE and MG. Correct as necessary.
Do not move the brush holders on either the PBE or the MG. clean them with plastic brush
Inspect commutator surface.
put bearings on MG shaft. They must be in the same locations as before. set as close as possible to original.
Reinsert MG shaft into MG casing. Use extreme caution. heavy and unwieldy.
Reaffix all bearing caps etc.
Reaffix all end covers, fan, etc.
Machine new brushes on milling machine for close approximation of commutator surface. Boring head is ideal for this task.
Check brush fit. if tight, slightly stone brushes until fit is correct.
Reaffix brush retaining springs/pushers. set correct tension.
Refit PBE unit to MG body.
Refit Pulleys.
Hand rotate MG and PBE units and apply commutator dressing stone to commutator surfaces in front of brushes. rotate as per correct rotation. Check brush face fit to commutator surfaces. correct as needed. Brushes are very fragile, use caution.
Once correct fit is established, fit pushers and set tension.
Reconnect everything.
gently brush out all commutator stone dust.
Hand rotate to check for binding etc.
Rewire.
Reconnect Power.
Test MG/PBE for functionality.
Run for 30 Seconds, cool down, run for 2 minutes, cool, run for 5 minutes, cool, run for 30 minutes cool.
Refit machine covers.
