The seal material will stretch as it is fitted to the
ring groove. If you let the piston sit with the seal
rings in place, it will become easier to install it in
to limit damage to the piston ring.
The housing will have a beveled chamfer on one
end of the piston housing. The piston is installed
through that end of the housing. Light taps with a
soft hammer may be required on the end of the
piston to move it into the housing.
To reinstall the piston, carefully work the piston ring
past the pinion gear opening in the cylinder bore.
While maintaining pressure on the end of the piston,
press the piston seal into the ring groove. As the
piston ring is compressed into the ring groove, the
piston will slide further into the bore until the piston
ring has passed through the pinion gear opening