It is highly recommended that you install the pinion on the tubing first, and then install the completed unit to the motor shaft......for a couple of reasons.
1/ The motor shafts on the FF050 motors are 1.5mm cold steel shafts,...they are soft, and can bend under the force of a pinion press.
2/ Most FF050 motors have a dust cap on the endbell end of the motor, and there is quite a gap between the end of the arm. shaft and the inner face of this dust cap. As you are not able to properly support both ends of the shaft in the pinion press, the press can cause the shaft to move too far into the endbell bushing, which can result in the comm. distorting at the tail end.
You can use a dremel and a file to remove this dust cap (and take out the horrible oil impregnated "fuzz" that most manufacturers use as packing on the endbell bushing on these motors), and this will eliminate this issue, but, still use care to ensure that the motor shaft does not bend.
Mr. Slotcar does make a neat little pinion for these motors ...8/9/10 T, (5.5mm dia.) that has a 1.5 mm id. with a 2.0mm "nub" on the end. They are a smooth fit on the 1.5mm motor shafts, (not loose enough to allow any runout) and need to be secured by either soldering or a drop of red locktite. I have done dozens using only a drop of locktite with no issues. If your motor has a knurled shaft end, it is advisable to file/grind the knurl a touch.
Attached is a pic. of the Mr. Slotcar "nub" 1.5mm pinion..........these are available from most shops.
Sorry for the piddly little shot of the pinions by themselves.......all I had.
The second shot shows one of these pinions on a Scaley motor.......if you need the pinion to be moved closer to the can end, you will need to file/grind the knurls.......if you do need to take the knurls down, put some power to the motor, the spinning shaft will ensure that you take down the knurl evenly, allowing the pinion to be properly centered on the shaft.
Cheers
Chris Walker

