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  • #5 low compression

    When the kid got this Jeep he also got another motor with it. The guy said he bought it off ebay from a mechanic in Greenbay. The 258 lower unit it self has supposedly 15k on it. He replaced the head with a reman 4.0 however the #5 cylinder is low on compression. I think I know where I'm going to start looking but the extra feedback never hurts any idea's?

  • #2
    How low of compression? My #4 was about 40 psi less than the rest, i turned out to be broken rings. The last time was 0 compression, and turned out to be this...

    Good luck, hopefully it's something simple!


    • #3

      About 12#, thats why I'm leaning more towards a turned ring or a valve not seating. If I heard it run or had it running it would be alot easier to diagnose. I'm only going by what the guy told me.
      I think I'm going to start with a valve adjustment and if that doesnt cure it pull the head and the pan and pop that piston out. What do you think?
      The motor wasnt ran after the guy installed the reman head he just did a compression check and put it in the back of his garage then sold it.


      • #4
        I'd check fora sticky/bad valve like you said, then pull the piston. It's got to be fixed either way, and if it's simple,you're only out the cost of gaskets.


        • #5

          Thanks for the lean too Hill Bill E . Incidentilly nice piston..


          • #6
            Originally posted by Kids Mechanic View Post
            Thanks for the lean too Hill Bill E . Incidentilly nice piston..
            Just another peice for the ''trophy''!! I'm saving parts tht I've broken on the CJ one day I'm going to weld them into a ''trophy'', with an estimate of howmuch $$$ went into it! So far I have a tranny (SR4, rebuilt 3 times!) rear axles, 2 pistons, driver side steering knuckle, 3 or 4 driveshafts.....the list continues!!


            • #7
              Maybe the valves didn't get lapped? What does the spark plug look like?


              • #8
                I had them same problem with #5 on my origional engine in 1997 and the piston eventually shattered. Luckily I new I was low for a while and could find another engine so I was ready for the changeout.

                I remember one of my fathers friends had me pull all plugs on the old engine and blow compressed air in them to "loosen any carbon build up". It helped for a while but then the piston just gave out.

                Also, how are the threads in the hole and the plug? Still a tight fit?

                Hope that helps.....


                • #9
                  Hill B,

                  Nice pic! I actually had to bring my shattered piston pieces in to my boss to justify my time off work!!! Ha!