In 1968 I bought a well organized pile of parts that was once a new Yamaha YA-6. The previous owner took it apart because the bike wouldn't shift gears (I guess that was before 1 year warranties) and then couldn't get it back together. I bought the parts for $75 and spent a winter putting them back together without a service manual. After assembly, the engine started right up, shifted into first gear and wouldn't shift any further. I eventually took the bike to a Yamaha dealer in Boston, who worked on it for a month, but couldn't get it to shift, either. He then sent it to the Yamaha distributor who did fix the bike by replacing one of the transmission cases, which apparently had a crack in it. I was only charged $100 for all of the work. Ah, the good old days.