After a painful attempt at rebuilding a Craftsman block grinder, leaving me wishing I'd never taken it apart, I stumbled upon a simple method to ensure proper alignment of the rotor and armature within the housing that I'd like to share in case it helps someone else.
After swapping bearings in my block the rotor would spin freely by hand. But under starting load the rotor wound scrub the armature, causing growling sounds and slow start up. Finally when I put larger grinding wheels on the block couldn't even start.
Upon disassembly I found scuffing marks as so, indicating poor alignment of the rotor within the armature:
The following is a simple writeup showing how to assemble a block while maintaining an even air gap between the rotor and armature. The pictures are from a 1/2hp flat-top mid 70's block.
You'll need 0.010" shim stock cut into 1/8" wide by about 4" long strips. I used brass. You may find a slightly different thickness is necessary but it's not a precise operation like adjust valves. If the 10 thou doesnt fit, try thinner.
Tear it down:
Install the rotor into the "back" half housing (the one that the armature bolts into). Put the free end of the rotor in a vise to stabilize. Install the armature and leave the four 1/4" head bolts loose. Slide the shims into the four sides of the air gap, leaving plenty of extra material to grab with pliers later. Do not try to spin the rotor until later after you pull the shims out.
Closeup of shim in the air gap:
Tap the armature gently on all sides with a soft hammer to equalize the stresses:
Torque down the four bolts holding the armature in place:
Install the other housing half:
Install the 3 long main bolts loosely. Set the block on a flat surface, ideally with the feet removed to ensure the halves sit in the same plane. Tap the armature and housing with the soft hammer again to let everything settle in. It's temping, but don't spin the rotor yet!
Torque the 3 long bolts evenly in a couple of passes.
Reach in with pliers and gently pull the shims out.
Yoink!
NOW you can give it a spin. Assemble the rest and you're ready for work.
After swapping bearings in my block the rotor would spin freely by hand. But under starting load the rotor wound scrub the armature, causing growling sounds and slow start up. Finally when I put larger grinding wheels on the block couldn't even start.
Upon disassembly I found scuffing marks as so, indicating poor alignment of the rotor within the armature:
The following is a simple writeup showing how to assemble a block while maintaining an even air gap between the rotor and armature. The pictures are from a 1/2hp flat-top mid 70's block.
You'll need 0.010" shim stock cut into 1/8" wide by about 4" long strips. I used brass. You may find a slightly different thickness is necessary but it's not a precise operation like adjust valves. If the 10 thou doesnt fit, try thinner.
Tear it down:
Install the rotor into the "back" half housing (the one that the armature bolts into). Put the free end of the rotor in a vise to stabilize. Install the armature and leave the four 1/4" head bolts loose. Slide the shims into the four sides of the air gap, leaving plenty of extra material to grab with pliers later. Do not try to spin the rotor until later after you pull the shims out.
Closeup of shim in the air gap:
Tap the armature gently on all sides with a soft hammer to equalize the stresses:
Torque down the four bolts holding the armature in place:
Install the other housing half:
Install the 3 long main bolts loosely. Set the block on a flat surface, ideally with the feet removed to ensure the halves sit in the same plane. Tap the armature and housing with the soft hammer again to let everything settle in. It's temping, but don't spin the rotor yet!
Torque the 3 long bolts evenly in a couple of passes.
Reach in with pliers and gently pull the shims out.
Yoink!
NOW you can give it a spin. Assemble the rest and you're ready for work.