Engine - the correct compression PSI ? | Ford Escort Owners Association (FEOA)
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Engine the correct compression PSI ?

Discussion in 'Tech & Repair' started by headmn, Jun 24, 2020.

  1. headmn

    headmn FEOA Member

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    i have a 1.9L '95 LX scort. i want to know what should be the
    compression be for my 1.9L? i have measured 127# to 132# on the
    4 cylinders with my tester. i have seen where some ppl are get-

    ting other readings with their particular testers. i have seen
    when it was written that the cylinders should should have 150+
    psi. i am in engine reassembly and honed . are my newly instal-
    led rings OK or should i try again? headmn







    =
  2. denisond3

    denisond3 Moderator Staff Member

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    I would say your readings are just fine. The pressure readings depend a lot on whether the throttle was open or just in the 'idling' position, the cranking speed, the number of times you let the engine turn over for each result, even the thickness of the motor oil used, and the native accuracy of the compression tester itself. If you put in new piston rings the results will change with engine use - fairly quickly at first, and much less when the engine has a 1000 or more miles on it. Even the compression tester would make a difference. I use one that screws into the spark plug hole, which pretty much eliminates any 'escape' of the air when the piston has comes to the top.

    I am one who leaves the throttle closed (foot off the gas), has all four spark plugs out during the job, and lets the engine turn over enough times that I hear the change in cranking speed for 6 or 7 complete sets of compression strokes - per each cylinder. I get about 130 psi to 150 psi most times, but these are with an engine that has a few years of use on it. I imagine I would get closer to 200 psi if I had the throttle open, on an engine that had been in normal use; i.e. with well seated rings. The important thing to me is to see the readings being fairly close across the four cylinders.

    I have never compression tested an engine right after I rebuilt it. I normally get the block honed, put new rings on the pistons, (after cleaning out the ring grooves), and with a light coating of motor oil on the cylinder wall. So far I have had consistent results; the cars run well, get mpg in the upper 30's on the open road, in the 20's in town. My 5-speed gets about 40 mpg on the interstates.
  3. Joey_Twowagons

    Joey_Twowagons FEOA Member

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    I did check the compression of my wife's Honda right after replacing the head after a valve grind and overhaul.

    The compression values were low for one or two cylinders. I started the car and let it run for a minute or so and then did another compression test, and this time they were all fine.
  4. headmn

    headmn FEOA Member

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    thank you all for a thorough and detailed look at the different situ-
    ations with Compression testing.different ways and even viscosities
    can have an effect on readings. hopefully, i will finish up and then
    cruise MODERATELY, not expecting to replace rings for another
    92250 miles. headmn
    denisond3 likes this.
  5. marclar

    marclar Administrator Staff Member

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    need to run the engine and break in the rings before doing a reliable compression test.

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