Mercury Mariner 4, 5 102CC Sail 1990 Outboard Service Shop Manual, Page 13Get this manual
Compression Check NOTE: Engine must be normal operating temperature (run to minutesprior to checking compression A
cold enginedry" cylinder will result in false readings1Remove spark plug
Propeller Chart
DiaPilc NobladesMaterial J.Aluminum 3-Aluminum 3-Aluminum 3-Aluminum ApproxGross Boal Wgt(lbs Up to 500 300 to 700 600 plus High Aeverse Thrust (Saill Workboat) Propeller Part No
2Inslall compression gauge in spark plug hole3Crank engine thru at least compression strokes with throttle wide open to obtain highest possible reading 4Check and reco rd compression The compression reading shou ld be at least 90 psi (620.5 kPa) lower compression indicates that cy linder is in some way defectivesuch as worn or sticki ng piston rings andlor scored piston and cylinder5Compression check is important because an engine with low or uneven compression cannot be tuned successfull to give peak performance II is essential, therefore, that improper compression be corrected before proceeding with an engine tuneup
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