Thanks for looking, guys.
What do you typically set the armature end play at for these bad boys?
As little as possible without anything binding Geary. The truth is that means a little more than on later and modern motors. The Mabuchis bushings were/are awful. The can bushing can be fixed, as was done here, with either a non-moveable bushing or a bearing. I didn't install this bearing, or even know what the source was. The ones I've seen that come with a bearing installed "look" OK, but they're junk and will self-destruct in no time. This one is a solid unit and fits the Mabuchi's oddball shaft size pretty well...but I prefer to have the flange on the inside of the can for obvious reasons. I don't know what's holding it in there...probably epoxy or something. Anyway, the end bell bushing (*actually, the end bell in general) is not an easy fix (outside of just cutting it out and installing a bearing strap using the end bell screw holes, which presents other issues. A tight setup can result in early failure of these motors, *especially if the arm isn't well-centered in the field, because of friction/heat. I don't have a "scientific" measurement...I just do them by what seems right.
Do you use 3/32" axle spacers?
Yes, sometimes I do, and they seem to fit the shaft at least as well as the *actual* spacers, but I save as many of the stock spacers as I can from junk motors.
What material do you prefer the spacers be made of when in contact with an oilite or a ball bearing?
Against an oilite, I *think* brass/bronze spacers make more sense, but any difference that steel might make in wear is probably very slight. There are some very nice steel spacers out there...precise and all the way down to super-duper thin, but there's one thing about them that sort of bothers me. On motors with strong magnets (NOT the standard Mabuchi magnets 
) , you can be installing the arm and have the spacers get sucked right off the arm. Then it's sometimes really difficult to get the little things back out. Funny, I once had this happen and couldn't figure out why the end play didn't change after adding the spacer. 
Do you have a favored method of winding the Kevlar on the commutator and welded connections?
All my arms (whether welded or soldered) get tied and epoxied, and I have settled on a way of tying them. I start out by passing the kevlar under one of the wires in the tiny space between the com spacer and the wire, wrap around a couple of times and then start going over and under each tab. When I'm using kevlar thread, I'll go over and under each tab at least twice. When I'm using a little heavier kevlar, just once over and under each tab to form an "x". After the last tab, I go back down under the com and wrap the wires at least once before knotting the kevlar. The knot also matters, because kevlar doesn't "like" to be knotted like say cotton. If you look up some of the knots used by the guys who tie flies, there are some neat ones, but I use sort of a modified square knot. I did have the knot fall apart once some time back, so I changed things up. I had always figured that the epoxy would make any knot suitable, but maybe I didn't make sure the knot was well-saturated on that arm. Anyway, since then I changed my knot and always make sure the knot and all the rest of the kevlar is saturated with epoxy.
-john
