BRP Johnson 4HP Service Manual page 102

POWERHEAD
PISTON PIN / CONROD / CRANKSHAFT
Conrod big end side clearance
Measure the clearance with the conrod installed on the crank
pin as shown in the figure.

Thickness gauge
Conrod big end side clearance:
Standard: 0.20 – 0.90 mm (0.008 – 0.035 in)
Service limit: 1.20 mm (0.047 in)
If the measurement exceeds the service limit, replace the
conrod assembly and/or crankshaft.
Conrod big end width:
Standard: 23.30 – 23.80 mm (0.917 – 0.937 in)
Crank pin width:
Standard: 24.00 – 24.20 mm (0.945 – 0.953 in)
Crank pin
Inspect the crank pin for uneven wear or damage. Measure
the crank pin outside diameter for out-of-round or taper using
the micrometer.
Out-of-round: A – B
Taper: a – b

Micrometer
Crank pin outside diameter difference
(Out-of-round and Taper):
Service limit: 0.010 mm (0.0004 in)
If the out-of-round or the taper exceeds the service limit,
replace the crankshaft.
Crank pin outside diameter
Standard: 27.990 – 28.000 mm (1.1020 – 1.1024 in)
6-28