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mowerman's Avatar

Join Date: Oct 2003
Posts: 23

12-31-03, 05:53 PM   #1  

Hello guys
My question is about compression.
What should be the compression reading
for a 4 cycle engine.Also for a 2 cycle engine.Finally got me a compression gauge to test with.Was needing to know a good compression to go by.I figure the cycles may be diffent. Thanks again for the help. mowerman

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snoman's Avatar

Join Date: Dec 2003
Posts: 326

01-01-04, 09:34 AM   #2  
I'm interested in hearing what some of the replies to this will be cause with compression releases and stuff I don't know how to achieve this either.


jughead's Avatar

Join Date: Oct 2003
Posts: 597

01-01-04, 03:45 PM   #3  
I've put a compression tester on lots of engines (2 and 4 cycle) and usually find between 80 and 110 lbs on a good engine. Even the Tecumseh with a compression release registers about 100 when being cranked by the starter motor. You could get a lower reading if you have to check an engine with a pull rope starter but even there I've been able to get 100 lbs on my tester on a variety of B&S, Tecumseh, Kohler, and Homelite engines. You could expect an engine to be hard to start if your compression readings get much below 70 or 80 lbs. Keep in mind that its always a good idea to make sure that your choke is off and the throttle wide open while doing a compression test to get unrestricted air into the engine so you can get an accurate reading. Failure to do the above could cause an inaccurate low reading and make you believe that there is something wrong with the valves or rings when everything is really fine.

cheese's Avatar
Forum Topic Moderator

Join Date: Jul 2001
Posts: 16,567

01-01-04, 10:10 PM   #4  
I agree that 80 lbs should be enough to start most any gas small engine. Compression release can be a factor in the readings, how fast the engine spins can also affect it. I don't use a compression guage much anymore. I like to hear the engine turn, and feel it (if it's pull start). That has proven more useful to me than a compression tester.

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