1981-1984 Official Honda ATC250R Shop Manual, Page 139Get this manual
CJ ATe NOTE , -
BRAKE MECHANISM (FRONT DISC BRAKE)
Install the piston with the concave end on the brake pad sideInsert the piston into the caliper cylinder
Install the piston with the end about 10 mm (38 in) projecting above the caliper
Wipe excess brake fluid off the caliper with clean cloth
Install the pin boots and bushing in the caliper and lubricate the inside with silicon grease