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Rebuild Advice

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  • Rebuild Advice

    Finally pulled my rear cylinder apart, and the piston is indeed shot.

    I have another cylinder that needs to be honed, but it's measuring a .076mm cylinder clearance on this used piston. I'm assuming at this point my best bet is a first over piston and have a cylinder bored to match.

    Any thoughts on the cause? Noticeable erosion above the first ring, and minor scuffing on the skirts.

  • #2


    • #3
      The wiki link is a nice touch

      So why the sudden knocking? It has been in the following configuration for 2seasons without issue

      Dual plug heads
      2003 ECU & TBs (no STV)
      1st gen cam swap
      full exhaust
      open top airbox

      running on 87octane from the same station

      I will say, it was running a hotter than usual (220F vs 200F) but never above 230 and I was trying to determine if it had a small coolant leak somewhere. That extra 20* push it over the edge to where I should have been running 93?

      I was expecting to see a blown head gasket, not a damaged piston


      • #4
        Could be heat or combo heat and fuel.


        • #5
          Do colder spark plugs help or not?


          • #6
            They can. I use CR9E but seen same damage with is as well.


            • #7
              You ever used the coldest CR10E? Manual has them as option.


              • #8


                • #9
                  Finally got everything finished up and went for a test ride. MUCH stronger feeling without a 40% leakdown on the rear cylinder! I went with single plug heads and removed the middle layer of the head gaskets. Went with CR9EIX plugs and will switch to 93octane as well as a little more detonation safety.

                  Found my coolant leak also. A pinhole leak in the radiator (due to a lowside in someone else's oil slick! ), only started seeping after it was hot and pressurized and just slow enough to mostly evaporate at 100+ degree days. But just enough that I had to keep topping off the radiator.

                  I was pulling the rings off the bad piston (pictured above), and the ring lands came out in chunks! Guess it was in even worse shape than I thought!