BRP Johnson 4HP Service Manual page 96

POWERHEAD
CYLINDER / PISTON / PISTON RING
Cylinder bore wear (difference)
Using the cylinder bore gauge, measure the cylinder bore in
the thrust and axial directions at the two positions A and B.

Cylinder gauge set
Check for the following:
•
Difference between the measurements at the two positions
(taper).
•
Difference between the thrust and axial measurements
(out-of-round).
Cylinder bore wear (difference):
Service limit: 0.100 mm (0.0039 in)
If the wear (difference) exceeds the service limit, rebore or
replace the cylinder.
Piston to cylinder clearance
To check the clearance, measure the following items:
•
Cylinder bore at 35 mm elevation from the gasket surface
at a right angle to the crankshaft pin.
•
Piston skirt diameter at 14 mm elevation from the skirt end.

Cylinder gauge set
Micrometer
Piston to cylinder clearance:
Standard: 0.010 – 0.040 mm (0.0004 – 0.0016 in)
Service limit: 0.100 mm (0.0039 in)
If the clearance exceeds the service limit, replace the piston
and/or the cylinder, or rebore the cylinder.
Cylinder bore:
Standard: 62.000 – 62.015 mm (2.4409 – 2.4415 in)
Piston skirt diameter
Standard: 61.975 – 61.990 mm (2.4400 – 2.4406 in)
6-22
A 35 mm (1.4 in)
B 60 mm (2.4 in)
14 mm
(0.6 in)