With a motor full of broken gears, we began scouring the internet for a source of replacement parts. Ebay turned up nothing but some random parts and inoperable starter motors. But according to some of the Aermacchi websites, it sounded like the "go-to" person was Ron Lancaster at Lancaster Aermacchi Sprint. We gave him a call and discovered that he sold out of the sets of gears that he had made, without plans for making additional sets. On the other hand, we could buy a new starter conversion built from a Honda Goldwing starter. It would work, but would look like an afterthought on the bike. Not so pretty. Sticklers for keeping the original Sprint 350's details, we kept searching.

05.07.20 Broadening our search to just "Aermacchi NOS Parts," opened up more options for finding the necessary individual components, starting with a set of two ring gears (#50022-73P). We needed only one, so the other one can go back on sale on Ebay one day. We also found a cheap-quality [overpriced!] gear puller on Amazon which helped to pry the broken ring gear out. Baby steps toward making this thing operable.

05.12.20 The Starter Motor Repair Kit (31437-73) arrived! Assuming they must had sold a bunch of these since we've seen a good number of old starters online with broken gear teeth. We promptly removed the cotter pins, pulled out the small planetary gears, and installed them into the Aermacchi – now complete with a full set of new gears. Hopefully, they don't blow up again. Ideally, we'd like to make a set of new, modern gears in a less brittle material to ensure the reliability of our starter. Maybe our talented friends at Additive Restoration can come up with a solution!

And the moment of truth…

We purchased the bike confident that it runs easily with the kickstart. But, like my old '73 Aermacchi Sprint 350, whose the starter motor was temperamental, this one just didn't work.

And so began the methodical process of troubleshooting…

04.24.20 This started with charging the tractor battery that the bike came with, which took about 40 hours to fully charge. The contacts were cleaned as well, so with that variable now out of the equation, we looked to the starter relay. 

04.26.20 We opened up the start relay to discover that it was manufactured by Bosch. Upon inspection, it looked to be in near perfect condition. ​There was some corrosion on the contacts which we removed with some fine grit sandpaper. It was reinstalled onto the bike and with the starter button pushed, we could hear it clicking. It was working like it should! What else could be the problem?

Further along the chain, it was time to inspect the Nippon Denso starter motor itself. We pulled the cover off the starter motor. Brushes looked good. Commutator looked good. Then we pulled the motor out of the housing and inspected each of the pads on it to make sure that there was no crossover current. Everything checked out in the tedious inspection.

So we hooked up the starter motor to the bike, with it out of the housing and it spun. Starter motor works.  

What wasn't working, however, were the planetary gears behind the start motor. The teeth on the gears appear to have been destroyed. Assuming one of the teeth broke off and wreaked havoc, thereby causing damage to the other gear teeth, including the ring gear. What a hot mess.