BRP Johnson 4HP Service Manual page 99

Piston ring end gap
Measure the piston ring end gap with the piston ring in the
lowest position of the cylinder bore.

Thickness gauge
Piston ring end gap
Standard:
1st 0.20 – 0.35 mm (0.008 – 0.014 in)
2nd 0.35 – 0.50 mm (0.014 – 0.020 in)
Service limit:
1st 0.70 mm (0.028 in)
2nd 1.00 mm (0.039 in)
If the measurement exceeds the service limit, replace the
piston ring.
Piston ring free end gap
Measure the piston ring free end gap.

Vernier calipers
Piston ring free end gap
Standard (1st and 2nd):
Approximately 8.5 mm (0.33 in)
Service limit (1st and 2nd):
6.8 mm (0.27 in)
If the measurement exceeds the service limits, replace the
piston ring.
CYLINDER / PISTON / PISTON RING
POWERHEAD
6-25