XJ550 Master Cylinder Question

Im currently rebuilding my braking system and my master cylinder is shot. I work at a motorcycle shop and we can order universal master cylinders that fit 7/8” bars. What bore size is the piston on a master cylinder from an 82 xj550 maxim?

My other question is, if my bore size is let’s say 1/2” can I put on a cylinder that has a 5/8” bore? It would just be pushing more brake fluid right? You just don’t want to go smaller than the stock size?
Thanks guys!

 

Ideally you want to stay with the same size. Going bigger on the MC side moves more fluid but you get less pressure, go too big and you’ll have less pressure and the brakes will have a wooden feel. Smaller MC results in higher pressure and you will lock them up easier. There’s charts online you can find but think of it like a lever and fulcrum, push down on the shorter side, the opposite side will travel further but you can’t lift as much weight and vice versa.

 

I forgot, the size will be stamped on your old master cylinder.

 

I've gone to smaller size on other bikes, more feel at the lever but more lever travel, I haven't ever had a bike I'd go bigger on