Compression test

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Bob Broihahn-S.W. Wi
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Compression test

Post by Bob Broihahn-S.W. Wi » Wed Jan 30, 2019 5:22 pm

I have a quick question, about a compression test on a "T" engine. I have several picture of the engine as it sits and wondering if a compression test can be done as the engine sits.
Thank you
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John.Zibell
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Re: Compression test

Post by John.Zibell » Wed Jan 30, 2019 5:52 pm

Install the hand crank or a starter and yes you can perform a compression test. You sure won't need to make sure the throttle is open!! Do remove all spark plugs to make it easier to turn over on either the starter or hand crank. You will only have compression on the cylinder where the gauge is installed. You may need an adapter for the compression tester. https://www.modeltford.com/item/5201CAD.aspx
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GrandpaFord
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Re: Compression test

Post by GrandpaFord » Wed Jan 30, 2019 7:45 pm

The easiest thing to do is to just crank it over by hand with the crank, with the ignition off and the throttle open. You can feel the compression. If the engine has not been run for a while the oil has drained out of the rings and there will not be much compression. Add some engine oil, a tea spoon or so, to the cylinders with the plugs out and put the plugs back in a try it again. If you turn it over slowly you can hear any leakage at the crankcase, the exhaust manifold, or the intake manifold. Turning it over quickly will give you a more accurate picture of the compression during running. This is a qualitative test and not quantitative. It will give you a rough idea. To be more accurate use the compression gauge and crank the engine fast with all the plugs out. Use the starter if you can.

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GrandpaFord
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Re: Compression test

Post by GrandpaFord » Wed Jan 30, 2019 7:48 pm

Since you have the manifolds off you can hear any valve leakage at each port.


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Re: Compression test

Post by Jim W » Mon Feb 11, 2019 7:47 pm

Hi, one of the problems with testing the compression on a low compression engine is not using the proper range of the gage. My opinion is the max gage pressure used should be twice the expected pressure of the engine. The standard gage pressures on many testers is 200-300 PSI. If one is used on a stock T , there is scarcely enough pressure to lift the needle. It also will be difficult to read minor differences between cylinders.

Sincerely, Jim Weir


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Re: Compression test

Post by Jim W » Mon Feb 11, 2019 7:49 pm

Hi, one of the problems with testing the compression on a low compression engine is not using the proper range of the gage. My opinion is the max gage pressure used should be twice the expected pressure of the engine. The standard gage pressures on many testers is 200-300 PSI. If one is used on a stock T , there is scarcely enough pressure to lift the needle. It also will be difficult to read minor differences between cylinders.

Sincerely, Jim Weir

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Re: Compression test

Post by DanTreace » Mon Feb 11, 2019 8:33 pm

Didn't have any trouble with a quality gage on my T engines. Pipe thread adapter from the local hardware store, easy to do test. The test doesn't really have to be such accuracy, the test is to see if the needle holds. Mind did, had to push the gage release button to get back to zero!


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Re: Compression test

Post by Charlie B in N.J. » Mon Feb 11, 2019 10:26 pm

As was mentioned a decent gauge will give you a proper reading. Do a dry then a wet test. Write the pressures down & don't trust to memory. Best way to tell your engine's internal condition.
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John E. Guitar
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Re: Compression test

Post by John E. Guitar » Mon Feb 11, 2019 10:59 pm

What a fine looking engine stand!


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Re: Compression test

Post by SurfCityGene » Tue Feb 12, 2019 12:58 pm

Dan, Nice gage But you need to be aware that the error tolerance of any gage can be very wide at both the upper and lower 1/3 of the range.
For our T's it would be most accurate to use a 100 PSI gage if available. Your reading looks really great!
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Mark Nunn
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Re: Compression test

Post by Mark Nunn » Tue Feb 12, 2019 1:06 pm

What would be a reasonable compression pressure for a stock engine, both dry and with oil added to the cylinder? Mine was in the range of 42-44 psi dry while hand cranking. I did not do a wet test. I want to retest using the starter.


tonny
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Re: Compression test

Post by tonny » Tue Feb 12, 2019 3:12 pm

i think a leak test is a better option than a compression test at tis stage.
you can check easy if the valves are leaking or pistion rings.

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Re: Compression test

Post by Charlie B in N.J. » Tue Feb 12, 2019 3:49 pm

Mark those #'s are pretty good. I prefer to take the low compressionT engine comp test cold as it gives a better indication of cold starting conditions. Take the wet test and see if the #'s rise. It would indicate ring wear. As to a leak test: it might show leaking valves but the air would always leak past cold rings where as the wet test would show the wear if any.
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