We had our second race on the vintage schedule this past weekend at Motopark. The weather worked out perfect and the track was in great condition. My Super Combat was laid up due to a loose fit on the lower steering head bearing race, so I had no choice but to race my Super Toad. I really enjoy racing the Super Toad but Motopark is a sandy track with some elevation changes where HP can make a big difference, so I would much rather be on the 125cc bike with that extra push when the throttle is twisted. Regardless, the Toad was the only choice so off I went. The bike performed well for the first two laps and I was having fun (as usual) until I heard a horrible grinding noise followed by a distinct lack of forward motion. I backed off on the throttle and gingerly dropped down a gear and where the noise went away. I limped the bike back the pits and put it on my bike stand (courtesy of the local dairy). As I played with the gearbox I became painfully aware that third gear was AWOL, which is sad because third is one of my favourites. Oh well, I'm done for the day I thought, but my brother was kind enough to lend me his vintage CR125 for the heritage class so at least I got to race, albeit on a bike that was a generation too old for the class I was racing. Getting back to the Toad, today was time for a teardown. First things first, off with it's head!
Well that's not right
I guess a new piston is in order.
Getting the clutch cover off, the first signs of transmission troubles:
Once the cases are split the carnage is obvious:
Here is a picture of the remains of the third cog:
Just to add insult to injury, I noticed this crank seal:
I'm wondering if the spring came off during assembly, while running or during the teardown.
Anyway, I know why the piston failed. It was a NOS part that I had in my parts stash. When I assembled it I noticed that the ring was a tight at one point in the groove (likely where it broke), so I took a small file and cleaned up the groove so the ring would fit correctly. Looking back, it was likely that the piston had been hit on the crown causing a crack that I failed to see. The piece then broke away once the engine was ran. I guess I was lucky that it did not damage anything else.
As for the transmission, I guess the Toad transmission is not quite up to the stresses imposed on it by a Super Rat top end. Any suggestions?
Brian
