Cylinder Compression - BRP Johnson 4HP Service Manual

PERIODIC MAINTENANCE

CYLINDER COMPRESSION

CYLINDER COMPRESSION
NOTE:
Figures shown are guidelines only, not absolute service limits.
Cylinder compression
(with decompression system):
550 – 650 kPa (5.5 – 6.5 kg/cm
Low compression pressure can indicate one or more of the
following:
•
Excessively worn cylinder wall
•
Worn piston or piston rings
•
Stuck piston rings
•
Poor seating of valves
•
Ruptured or otherwise damaged cylinder head gasket
Test procedure
1. Start and warm up the engine, then shut the engine off.
2. Remove the spark plug.
3. Install the compression gauge into the plug hole.
 Compression gauge
Compression gauge adaptor (12 mm)
4. Disconnect the safety lanyard from the emergency stop
switch.
Disconnect the safety lanyard from the emergency stop
switch prior to cranking the engine.
This will prevent any residual fuel discharged from the
cylinders from being ignited by a spark discharged from
the spark plug cap.
5. Move and hold the throttle control grip in the full-open
position.
6. While cranking the engine with the recoil starter, note the
maximum compression pressure reading on the gauge.
2-16
2
, 78 – 92 psi)