Generac 86640 - Manual (Page 29)

Measuring Compression Pressure (Continued)
then crank the engine and read the compression pres­
sure. The pressure reading shouid be as follows:
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MINIMUM n 164 psi (11.5 kg/cm^) at 350 rpm
DIFFERENCE BETWEEN CYLINDERS SHOULD NOT
EXCEED 14 PSI (1.0 kg/cm^)
If the compression reading is low in any cylinder, pour a
small amount of clean engine oil into the cylinders through
the spark plug opening. Then, retest compression and eval­
uate as follows:
D If compression pressure increased after adding the oil,
check for worn or damaged piston rings or worn cylinder
walls.
n If pressure did NOT increase after adding oil, valve(s)
may be sticking or seating improperly.
D If compression in any two adjacent cylinders is low and
adding oil did not increase compression, check for a
leaking head gasket
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