BRP Johnson J30TEL4SUA 2007 Service Manual page 155

Check the water jackets for clogs or obstructions.
1. Water jacket
Inspect the cylinder walls for scratches, rough-
ness, or ridges which indicate excessive wear. If
damaged or worn, rebore the cylinder and use an
oversize piston.
Use a cylinder gauge to measure the cylinder
bore in the axial direction (vertical line following
crankshaft) and the transverse direction (horizon-
tal line across crankshaft). Take measurements at
two different depths: 2.0 in. (50 mm) and 3.5 in.
(90 mm).
2.0 in.
(50 mm)
1
001544
3.5 in.
(90 mm)
001545
PISTON, CYLINDER, AND CRANKSHAFT
The difference between the two depth measure-
ments is the cylinder bore taper.
The difference between the axial and transverse
measurements is the cylinder bore out-of-round.
The service limit for cylinder bore wear is 0.004 in.
(0.10 mm). If either the taper or out-of-round mea-
surement exceeds this specification, rebore or
replace the cylinder.
Use a micrometer to measure the piston diameter
at a point 0.75 in. (19 mm) above the piston skirt
at a 90° angle to the wrist pin bore.
Cylinder Bore and Piston Skirt Specifications
Cylinder Bore Diameter
Piston Skirt Diameter
To find the piston-to-cylinder bore clearance, sub-
tract the piston skirt diameter from the previous
cylinder bore measurement at a depth of 2.0 in.
(50 mm).
If the measurement exceeds the service limit,
replace the piston and/or the cylinder, or rebore
the cylinder.
Piston-to-Cylinder Bore Clearance
0.0008 to 0.0016 in.
Standard
Service Limit 0.004 in. (0.10 mm)
POWERHEAD
2.5591 to 2.5598 in.
(65.000 to 65.020 mm)
2.5579 to 2.5587 in.
(64.970 to 64.990 mm)
001546
(0.02 to 0.04 mm)
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