what size is stock? how big can you go?

[chamberlain31c]

what size is a stock 87 piston and how much can a stock cylinder be safely bored? also what years did the long rod package come in stock? mine has the long rod but not sure if its still factory or someone has worked on the motor.

[87R_Racer]

66mm is stock. I'm pretty sure you can go up to 68mm with the long rod crank & 87-89 style piston. 86 models had a shorter rod. You can use a 86 style piston and a 5mm spacer plate and go up to a 69mm piston.