Yamaha SR400 2014 Service Manual

ENGINE INSPECTION5-1EAS2RD1039ENGINE INSPECTIONEAS20720MEASURING THE COMPRESSIONPRESSUREThe following procedure applies to checking andadjusting the compression pressure.TIPInsufficient compression pressure will result in aloss of performance.1. Measure:• Valve clearanceOut of specification Adjust.Refer to “ADJUSTING THE VALVE CLEAR-ANCE” on page 3-5.2. Start the engine, warm it up for several min-utes, and then turn it off.3. Remove:• Spark plug cap4. Remove:• Spark plugNOTICEECA20470Before removing the spark plug, use com-pressed air to blow away any dirt accumulat-ed in the spark plug well to prevent it fromfalling into the cylinder.5. Install:• Compression gauge “1”6. Measure:• Compression pressureOut of specification  Refer to steps (b) and(c).▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼a. With the throttle wide open, kick the kickstart-er lever until the reading on the compressiongauge stabilizes.WARNINGEWA2RD1003To prevent spark generation, spark plug leadshould be grounded before cranking by thekickstarter.b. If the compression pressure is above themaximum specification, check the cylinderhead, valve surfaces, and piston crown forcarbon deposits.Carbon deposits  Eliminate.c. If the compression pressure is below the min-imum specification, pour a teaspoonful en-gine of oil into the spark plug bore andmeasure again.Refer to the following table.▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲7. Install:• Spark plug8. Connect:• Spark plug capCompression gauge90890-03081Engine compression testerYU-33223Extension90890-040821Standard compression pressure(at sea level)1050 kPa/700 r/min (10.5kgf/cm2/700 r/min, 149.3 psi/700r/min)Minimum–maximum910–1180 kPa/700 r/min(9.1–11.8 kgf/cm2/700 r/min,129.4–167.8 psi/700 r/min)Compression pressure (with oil applied intothe cylinder)Reading DiagnosisHigher than withoutoilPiston ring(s) wear ordamage  Repair.Same as without oilPiston, valves, cylin-der head gasket orpiston possibly defec-tive  Repair.Spark plug25 Nm (2.5 m·kgf, 18 ft·lbf)T R..