Ok, here is what I did. I installed metal pinion gears in place of the top 2 gears. I am still using the plastic bottom gear as I have never stripped one of those out.
I used the stripped out gear as a spacer on the top shaft, ground a small flat for the set screw to tighten on, and put the e-clip back on to keep proper alignment. The middle shaft is cut from a piece of 5mm rod I had, but you could use a drill bit (5mm or a #9) or something close to 5mm and make it work.
On the middle shaft I put a spacer on each side of the gear to keep the shaft centered in the bearings, probably not necessary but I wanted to make sure it was done right.
Here you can see it assembled, this mod eliminates the "slipper" clutch in the process. I still use the stock plastic bottom gear, like I said earlier, I have never stripped one of those out. So far I have abused this setup quite a bit with the 27t on 3s and have had no issues.
I used a 15t mod1 pinion Dynamite #2635 for the top gear and 22t mod1 pinion Integy #23176 for the middle gear. Those were the gears I could find easily, but looking a little harder I found the Hot Bodies gears #67579 and #67566 have an even better mesh with each other and the plastic gear. I would recommend the hb gears, you can get them at Tower for sure for about $20 for both.
Also, I cut the 5mm shaft for the middle gear to 1.140" long. You will have to remove the little plastic reducer bushing in the bearings for this shaft.
Sorry if this is a little confusing, I took a couple posts from a different thread and put it all together in this one.
