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What is normal comression test results?


BruceH

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What is acceptable compression test results on a Kohler 10 hp engine? 12 HP engine? B-110 ? The compression ratio is 7 x 1 I think. Does that have any bearing on what the compression test results should be? Tuff
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Tuffy, The 7:1 ratio indicates the engine will compress the intake pressure (normally atmospheric (14.7 psi) 7 times. This would give 102.9 psi on a compression test if the cylinder has no leakage. But, small engines normally have a compression release of some sort to make them crank easier so a compression test will not read the calculated valve. B & S has a procedure they recommend. Something to do with turn the engine by hand and see how far it bounces back. You need to consult a repair manual or knowledgeable B & S dealer/mechanic. Hope this helped, Roy
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The 102.9 lbs./sq. in. would be read at sea level.As you go higher that figure gets less. Atmospheric pressure at your altitudeXcompression ratio=compression corrected for one's particular altitude.As JN said any reading between 75-125 lbs. is normal for these engines. dlc
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dlc, If you're going to get technical on me you are correct. The actual pressure should be corrected for altitude, and temperature. 14.7 is the nominal value for atomspheric pressure at sea level and, if I remember correctly, 70°F. Roy
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Now that I think of it I think many of todays engines are using a release of one sort or another. Old Kohlers may or may not have compression release. Old B&S did not use it. 50-75 psi could indicate a compression release. Check the reading first by cranking with the starter. Make sure throttle is fully opened. Then rig it up so that you can wrap a rope and spin it over backwards. If it reads a bit more psi backwards then a release is indicated. You could also check the cam by removing the cover - if it has spring weights on it then it is a centrifical compression release. 75-125 psi is normal for non-compression release engines. Above and below these indicates something is out of the ordinary. Oil leakage can sometimes raise reading after engine is warmed up. Watch your gauge accuracy. We checked three different ones from three different mechanics and resulted in three different readings by 25%.
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