2001 Polaris Sportsman 400-500 DUSE and H.O. Service Manual, Page 46Get this manual
MAINTENANCE
COMPRESSION TEST
NOTE: 4-Stroke engines are equipped with an automatic decompressorCompression readings will vary in proportion to cranking speed during the testAverage compression (measured) is about 50-90 psi during compression testSmooth idle generally indicates good compressionLow engine compression is rarely factor in running condition problems above idle speedAbnormally high compression can be caused by decompressor malfunction, or worn or damaged exhaust cam lobesInspect camshaft and automatic decompression mechanism if compression is abnormally highA cylinder leakage test is the best indication of engine condition on models with automatic decompressionFollow manufacturer's instructions to perform cylinder leakage test(Never use high pressure leakage tester as crankshaft seals may dislodge and leak)