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Compression test
Posted: Fri Nov 13, 2020 11:30 am
by john in kzoo
Guys,
Interested in doing a simple compression test. A couple of questions 1. Warm or cold engine? and 2. All plugs out as each cylinder is being tested?
Thanks
Re: Compression test
Posted: Fri Nov 13, 2020 11:42 am
by Mark Nunn
Don't forget to fully open the throttle during the tests. You can't compress air that can't get in.
Re: Compression test
Posted: Fri Nov 13, 2020 12:45 pm
by RajoRacer
1: I prefer warm - 2: yes & 3: what Mark said !
Re: Compression test
Posted: Fri Nov 13, 2020 1:28 pm
by Mark Gregush
It is ok to have the throttle closed or open, I really have never seen a difference between the two. I do my test cold, I am more interested in starting compression then running. Again, you can do them both to see how much difference between the two readings.
Re: Compression test
Posted: Mon Nov 16, 2020 7:53 am
by john in kzoo
Compression test completed Saturday on a very cold engine (30 degrees) got 45#, 40#, 40#, and 40#. Plugs looked good #1 was sooty though
Thoughts??
Re: Compression test
Posted: Mon Nov 16, 2020 1:31 pm
by Tim Rogers
Run the wheels off of it or do a complete rebuild.
Re: Compression test
Posted: Mon Nov 16, 2020 1:52 pm
by Quickm007
How to do a compression test on engine without starter ?
Re: Compression test
Posted: Mon Nov 16, 2020 1:54 pm
by john in kzoo
I opt for running the wheels off........
Quickm007 - Crank and crank and crank
Re: Compression test
Posted: Mon Nov 16, 2020 2:53 pm
by Fire_chief
Mario, it is still the same process.
The only thing different is that you get to turn the engine over with the crank
Re: Compression test
Posted: Mon Nov 16, 2020 2:58 pm
by kmatt2
Your cold compression test numbers, 45,40,40,40, would sujest why #1 plug was sooty. You are getting a little oil past the rings in #1 and #1 plug has a intermitid misfire. Try doing a wet compression. test with a little oil in the cylendars and all numbers will come up, with #1 coming up the least. Your cold dry numbers of 40 lbs are not that bad. I would keep driving the car, keep up with your maintenance and check the #1 coil & timer connections, replace #1 plug if needed.
Re: Compression test
Posted: Mon Nov 16, 2020 4:21 pm
by john in kzoo
Thanks Guys.....
Re: Compression test
Posted: Mon Nov 16, 2020 5:59 pm
by Charlie B in N.J.
I much prefer comp testing a low comp engine like the T when it’s cold. It gives a truer situation concerning starting the T when cold. Testing hot will give a false reading regarding cold starting. A modern with a comp of say 150 lbs. or better is relatively in affected by a 5 or 10 lb. drop. On a T that could be the difference between easy starting or not on a cold day. Do a dry then a wet test with the choke & throttle wide open. Write the results down. Don’t trust to memory. A VERY informative test concerning your engines condition. Especially if you’re pulling the head for no reason.
Re: Compression test
Posted: Mon Nov 16, 2020 6:23 pm
by Oldav8tor
Sooo.... what is the "good" compression range?
Re: Compression test
Posted: Mon Nov 16, 2020 6:30 pm
by Tim Rogers
55 PSI would be nice...
Re: Compression test
Posted: Tue Nov 17, 2020 9:34 am
by Quickm007
Thank you guys, I will crank, crank and crank but my shoulder is painfull right now. Hope I will recover soon...

Re: Compression test
Posted: Tue Nov 17, 2020 11:00 am
by john in kzoo
It's really easy with all but one plug out and the throttle positioned all the way open as well
Re: Compression test
Posted: Tue Nov 17, 2020 1:33 pm
by KeithG
Super Mario, Befriend a football player with wide shoulders and strong arms....
Keith