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By zuburg - 10 Years Ago
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I finally did another compression test on my 239. I did the test again because I forgot to do the first test with the accelerator wide open and I wasn't able to get the compression hose on all the cylinders. I have the numbers for cylinders 1 thru 7 because I still couldn't get to no. 8. I'm sure the numbers indicate issues but thought I would throw them out to see what the experts say they mean.
Cyl. Compression
1 115
2 90
3 85
4 90
5 105
6 120
7 110
8 ?
thanks
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By snowcone - 10 Years Ago
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You need to go and do it again with a couple of squirts of engine oil in each cylinder and then post up the results for a comparison.
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By Talkwrench - 10 Years Ago
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Do it again, get a good screw in type of compression tester. Make sure the battery is strong, warm engine and yes WOT. ALso note the first stroke the tester makes, usually bounces up to around 70 PSI or so, this can tell things too, give it a few good cranks so it tops out . then if you have levels more than 10% difference between the cyls you may have some issues. As suggested if they are low a tea spoon of oil into the cyl and check the reading again.
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By Ted - 10 Years Ago
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The rule of thumb for cranking compression readings is no more than 10% difference between the lowest and highest values. That's with the throttle blocked in a wide open position. Whether you are using 8½ pounds or 12 pounds as your range value, your total range of values still exceeds the 10% rule. At this point, you can put oil in the low reading cylinders and see if those numbers come up. If they do, then that is indicative of a ring sealing problem. Another option is to perform a leak down test on all the cylinders which will give a better indication if the problem resides in either of the valves and/or the rings. Leak down testers come either in a dual gauge or single gauge variety but either is effective when performing that particular test.
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By Kahuna - 10 Years Ago
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Because this is a solid lifter engine, you may also give some thought to adjusting the valve lash on all cylinders, then retesting.
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