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Farmall A 1941

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Tom in Iowa City

Member
I am interested in a Farmall A that a friend owns. 1941. I want to do a compression test first. Please tell me EXACTLY the steps to follow, concerning 1) open throttle, 2) choke adjustment, all or only one sparkie removed at a time, etc. Thank you. ALSO, what are the NUMBERS that are minimum and good for compression? Thanks, Tom
 
run a dry and then a wet test. all plugs out, throttle wide open choke off. run test, write down each reading. then pump 3-4 squirts of motor old in each cylinder from a pump oil can,, crank motor a few times and re- run test. dry, minimum of 80 psi with no more than 10-15% variation between cylinders. if you get a big increase in cylinder pressure after adding the oil, suspect worn rings.
 
Just be sure not to add too much oil. I have seen that happen before and the cylinder becomes hydraulicly locked. Then when you remove the compression tester oil squirts out everywhere.
 
I would leave the plugs out when doing the test. That way you do not put any undue wear on the battery and starter. I teach auto tech in a high school and every book and film I have says to remove the plugs. I was (still am I guess) an automotive technician and I always do that too.
 
If the engine is runnable, the test results will be more accurate if the engine is warmed up first.
The cylinders will be oiled from just being run.
Leave the ignition OFF, all plugs out, throttle wide open, choke in the run position, (you want as much intake air as possible to give best test results).
Crank with fully charged battery, listen for the compression pressure buildup (compression stroke) and do each cylinder the same number of compression strokes.
Good luck.
 
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