| cappy39 | -- 01-28-2010 @ 4:07 PM |
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Hey guys I appreciate your advice. What is an acceptable range for the compression. Mine is stabilizing between 60 and 70. This seems pretty low to me, but I am new to flatheads. Mark
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| ford38v8 | -- 01-28-2010 @ 5:18 PM |
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Mark, I'd think that if they are all within a range of 10 lbs, you're good, even if they are all lower than yours. Alan
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| 37RAGTOPMAN | -- 01-29-2010 @ 6:04 AM |
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It all depends , one gauge might read one pressure, while a different guage will read a different amount of pressure, make sure you lock the throttle open,while doing this test, another test would be with the engine running using a good vacuumn gauge,the needle should be steady,if it wobbles back and forth,you may have some valve problems, its amazing how a good vacuunm gauge what it can tell you about your engine, most of the older vacuumn gauges have a dial with when the pointer points to a certain number or color section whats going on, this is also a great way to ajust the carb, if you buy a AMERICAM made comppression gauge from SNAP-ON would probabaly give the most accurate reading, but as long as they are with in 10-15 lbs you should be ok, my 2 cents worth, 37RAGTOPMAN
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| cappy39 | -- 01-29-2010 @ 6:59 AM |
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Thank you They are definitely within the range, but does it matter that they are around 60-70 lbs? Mark
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| supereal | -- 01-29-2010 @ 12:23 PM |
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When compression testing, it is necessary to remove all spark plugs to allow the engine to crank rapidly while the throttle is blocked open to provide maximum intake of air. While compression testing is an acceptable way of determining whether any cylinders are substantially lower than others, the best test is a "blow down". The piston is placed at the top of the compression stroke, and compressed air is inserted thru a fitting that screws into the plug hole, and has a pressure gauge attached. The air is then shut off, and the gauge is observed to see how long it takes for the pressure to fall. Listening at the carb and tailpipe can give a good indication of whether you have valve leakage.
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| deluxe40 | -- 01-29-2010 @ 1:43 PM |
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Cappy39 - If there aren't any other problems ( e.g., excessive smoke, oily plugs), a compression reading of 60-70 lbs. should be OK. My '40 has averaged about that for the last few years and it runs smoothly and keeps on going. It's not as powerful as my new '41 engine that averages about 110 lbs., but it's still OK.
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| Stroker | -- 01-29-2010 @ 2:57 PM |
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If you elect to go with the "blow down" a/k/a "leak down" test, make sure you have the motor locked in position. If in the car, you can do this by putting it in low gear, otherwise you will need to secure it with a large wrench at the crank pulley. As Supereal states, this is the most definitive form of compression test.
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| cappy39 | -- 01-29-2010 @ 8:11 PM |
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Thanks Guys!
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