Engine System
36
Service Manual – PBU Propane Floor Burnisher
Interpreting the Results
•
Because compression results will vary from engine to engine, there is no specific “normal” compression
value However, the minimum acceptable compression for this engine is:
Min Comp: 483 kPa (70 psi)
(hot engine)
• High compression is typically a sign of carbon buildup in the cylinder Remove the head and clean buildup
from the head and piston crown Also check the
•
If the first compression pulse is more than half the total compression after 5 pulses, and the total
compression is low, then the most likely cause is a valve that is not closing or sealing properly Check the
described on page 38 Check the
Valve and Seat Inspection described on page 42
• If the compression is low, refer to the Wet Test below to isolate whether the cause is rings versus valves
Wet Test
If the compression is low, you may wish to perform a wet compression test by adding a small amount of oil
to the cylinder before repeating the compression test The additional oil will improve a poor piston ring seal,
but will not improve the seal from a bad valve
Important:
For this test to be successful, the small amount of oil must evenly spread across the face of the
piston So the machine must be tipped up so that the cylinder is pointing upward It cannot be completed in
a horizontal position
1 Tip the machine up so the tested cylinder is facing upward
2 Using a syringe or small oil can, inject about 5mL (1 tablespoon) of clean engine oil into the spark plug
port
• Don’t put in too much oil or you could damage your compression tester
• Do Not
install a spark plug in the cylinder or you could seriously damage the engine
3 Manually turn the engine a couple of times to help spread the oil across the cylinder
4 Reinstall the compression tester and repeat the compression test
• If the new compression reading did not appreciably increase (less than 5 psi increase), then the
problem lies with the valves
• If the compression appreciably increased, then the piston rings are warn or the cylinder walls are
scored
5 After the test is complete, crank the engine several times without a spark plug to clear the cylinder
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