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Dauntless V6 Compression

Discussion in 'Early CJ5 and CJ6 Tech' started by PA CJ, Jun 6, 2017.

  1. Jun 6, 2017
    PA CJ

    PA CJ Member

    Joined:
    Nov 20, 2015
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    70
    Who has some cylinder compression numbers on a rebuilt dauntless motor? What about someone who's got 20-30k miles on a rebuild? Over 100k miles?

    I'm looking for actual compression test results.

    I've got two dauntless motors and they both check out around 95-105 psi on the cylinders. Adding oil only gains about 5psi, borescope shows decent cylinder wall condition, no significant scoring can be seen.
     
  2. Jun 6, 2017
    Tom_Hartz

    Tom_Hartz Member Sponsor 2019 Sponsor

    North Carolina
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    Apr 9, 2014
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    Mine is at 200 to 215 psi. The engine was built by a performance shop for the previous owner. Not sure what all was done but it runs good.
     
  3. Jun 6, 2017
    PA CJ

    PA CJ Member

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    Wow that seems pretty high
     
  4. Jun 7, 2017
    Alan F

    Alan F Sponsor Sponsor

    SE TX
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    Jun 16, 2015
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    When I got my Jeep it wasn't running. First thing I did was a compression test. It ranged from 0-140. I had a blown head gasket and other mechanical maladies. I rebuilt the top end only as the cylinders looked decent and the engine wasn't sludged up. I changed the cam (and differing cam timing events will change the compression readings) and compression is now in the 135-150 range all over (frankly a little more variation than I'd like to see). All the valve seats were also shot. I have no idea how many miles are in this engine but I think it suffered from lack of proper lubrication. It could be lack of lead in the fuel to lack of oil changes due to wear on the cam and lifters.
     
  5. Jun 7, 2017
    mike starck

    mike starck Member Sponsor 2019 Sponsor

    salem,oregon
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    The 1971 that was reported to have 40,000 miles. Compression with fully charged battery,clean battery cable connections,starter in good condition,throttle blocked wide open was 165 lbs all six cylinders. Non Cal. emissions /9:1 compression
     
  6. Jun 7, 2017
    tarry99

    tarry99 Member Sponsor

    Northern California
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    Oct 29, 2012
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    3,779
    Compression testing at it's very best is just a snap shot look at an engines internal condition..........as readings can vary based on many variables inherent during the test.......a leak down test gives a far better condition report on individual cylinders while also giving the trained eye the ability to target where the potential leak is coming from............

    For me a far better reason for using a Compression test is to better understand cam timing in the since of how that relates to cylinder trapping an incoming fuel charge volume to be compressed and burned...........
     
  7. Jun 7, 2017
    montanacj

    montanacj Sponsor Sponsor

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    I want to say I had similar numbers on the compression test of the renegade 1 that I purchased last year somewhere in the 100-120 range, that's at @3000 ft of altitude. I agree with Tarry that a leak down is more informative.
     
  8. Jun 7, 2017
    mike starck

    mike starck Member Sponsor 2019 Sponsor

    salem,oregon
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    I think most know the difference between a simple compression test and a leak down test.All that was said is true, but that wasn't the OP's question.Thanks anyhow.
     
  9. Jun 7, 2017
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    My $.02-

    Those engines don't have much life left in them.

    The borescope may show nice looking cylinder walls but it's not telling you how worn down they are, only pulling the heads & checking the ring ridge will do that.

    A leak down tester is easy & relatively cheap DIY build- it will tell you whether you're loosing compression at the rings or the exhaust valves or the intake valves or the head gasket.

    H.
     
  10. Jun 7, 2017
    OzFin

    OzFin Vintage Jeep Guy

    Michigan
    Joined:
    Jul 16, 2007
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    Motor purchased with unknown mileage.
    [​IMG]

    Fully charged battery, throttle wide open. Compression results all averaged within 10 psi of this.
    [​IMG]

    And yes, leak down testers are awesome.
    Oz
     
    montanacj likes this.
  11. Jun 7, 2017
    PA CJ

    PA CJ Member

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    Nov 20, 2015
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    I've done a leakdown test on the 225 in my 2a and it's about 40% leakdown all the way around. Seemed to be all going into the crank case past the rings. So it's kind of suspicious that adding oil to the cylinders doesn't raise the compression at all. But the motor still runs ok, it's hard to start when it's cold though.

    Picking up a complete core motor that has similar compression to rebuild so I can still drive the 2a around in the mean time.

    Was kinda curious as to what everyone else's situation was and how fast these things wear down. Supposedly the 225 in the jeepster was rebuilt 35k miles ago per the previous owner. We all know how that one goes though.....
     

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