Like the title says, wanting to get either a jackshaft or TAV for my stepsons stock 97cc new style doodle. Does anyone make either for this bike? We ride our minis at camp that have a few pretty decent hills, and needless to say, he's practically pushing his bike towards the top. I know these engines aren't the best, but buying another one just to modify for his bike isn't happening. Just would like to get the most out of what he has now. Do these engines have a 5/8 shaft or is it 16mm? That seems to be something I can't seem to get a straight answer on. Any suggestions?