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  • Compression test fail

    Hello all, I have been searching through many posts and have found plenty of info so far. My situation is this, 1998 TLR - I destroyed 4th gear. I decided to roll the dice and swap the motor. Only problem is that the front cylinder just failed a compression test biblically. So, what can I do? I now have a motor with a hosed gearbox and a motor with a hosed cylinder. Could I pull just the piston, head, and cylinder without splitting the case? I figure new rings and some honing would be a good thing to do. Any thoughts on manufacturers? Any advice would be appreciated.

  • #2
    Re: Compression test fail

    I would swap the front and rering the rear. I would never just do 1 cylinder. Good luck.

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    • #3
      Re: Compression test fail

      Originally posted by mudduck9 View Post
      I would swap the front and rering the rear. I would never just do 1 cylinder. Good luck.
      Do I have to split the case? It looks possible to take off the head, cylinder and re-ring. I'm a little nervous about opening the entire motor.

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      • #4
        you don't have to split the cases to change piston rings.

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        • #5
          Re: Compression test fail

          During the compression test is the gas going into the sump, i.e. past the rings or out the valves? Redo the test and squirt a small amount of oil into the cylinder, If the test result goes up (the reading) then its rings as the oil will help seal them and increase the reading. If the reading stays the same, take the header pipe(exhaust pipe off) the suspect cylinder and squirt some CRC or similar around the back of the valves and turn the motor over. If on compression when both valves are closed it bubbles around the valve seats, then it may need the seats to be recut and the valves faced. This is the better scenario as you only have to pull a head off to fix!!!!!!

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          • #6
            Re: Compression test fail

            Ok what IS the compression in the front cyclinder? The exhaust cam has a decomp device and will cause low compression in that cyclinder until almost starting rpm. Check the manual for the spec compression for that hole.And again I ask the question, what is your compression in the cyclinder?T.L.
            sigpic391 lbs or 177.34 kg LIST OF MODS ,The Short List ,The frame Is Stock.

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            • #7
              Re: Compression test fail

              Originally posted by TerryLemmons View Post
              Ok what IS the compression in the front cyclinder? The exhaust cam has a decomp device and will cause low compression in that cyclinder until almost starting rpm. Check the manual for the spec compression for that hole.And again I ask the question, what is your compression in the cyclinder?T.L.
              I saw nothing on the front cylinder. I had about 150 psi on the rear.

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              • #8
                Re: Compression test fail

                Originally posted by TerryLemmons View Post
                Ok what IS the compression in the front cyclinder? The exhaust cam has a decomp device and will cause low compression in that cyclinder until almost starting rpm. Check the manual for the spec compression for that hole.And again I ask the question, what is your compression in the cyclinder?T.L.
                I had nothing on the front, 150 psi on the rear. I'll try the oil suggestion later today.

                Comment


                • #9
                  Re: Compression test fail

                  Originally posted by jskidmore View Post
                  I'll try the oil suggestion later today.
                  Did you read what terry said and what I said on TLZ ?

                  You cannot do a compression test on a TL engine without wedging open the camshaft decompressors

                  You can do a leak down test if you have the kit and don't need to touch the cams

                  Last edited by Sam; 09-15-2010, 08:32 AM.
                  sigpic
                  TLS for Supercharged.....................

                  TLOTM Nov 04, Bitchin' Bike Contest July 07, July 2010

                  PM Me for Help & Prices with GSXR/Busa Radial Fork Conversion Kits

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                  • #10
                    Re: Compression test fail

                    A leak down test is basically using compressed air on the cylinder and holding it and waiting to see how low it takes to bleed off, correct? So, do you know a good way to rotate the motor to get to TDC?

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                    • #11
                      Re: Compression test fail

                      Originally posted by jskidmore View Post
                      A leak down test is basically using compressed air on the cylinder and holding it and waiting to see how low it takes to bleed off, correct? So, do you know a good way to rotate the motor to get to TDC?
                      Take the inspection cap out of the left hand engine cover and behind that is a 17mm bolt on the end of the crank you can turn
                      sigpic
                      TLS for Supercharged.....................

                      TLOTM Nov 04, Bitchin' Bike Contest July 07, July 2010

                      PM Me for Help & Prices with GSXR/Busa Radial Fork Conversion Kits

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                      • #12
                        Re: Compression test fail

                        Originally posted by Sam View Post
                        Take the inspection cap out of the left hand engine cover and behind that is a 17mm bolt on the end of the crank you can turn
                        OK, I didn't get so far as to do a leak down test, but I did do a compression test on the 98 motor and the front cylinder read 120 psi. I've ordered new rings. I'm thinking of taking the front cylinder and piston from the 98 motor and putting it on the 03. That should resolve the problem, correct?

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                        • #13
                          Re: Compression test fail

                          why not try it and find out.

                          you haven't taken any other advice so far.
                          www.cycleinnovations.com.au

                          It never ceases to amaze why people ask for advice then when I give it they either ignore it or argue against it.
                          But then I don't know all that much about TL's

                          wwjd.......what would jimmy do.

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                          • #14
                            Re: Compression test fail

                            Originally posted by The Ring-In View Post
                            why not try it and find out.

                            you haven't taken any other advice so far.


                            Why just stop at rings.
                            "I spent most of my money on Scotch, women and cigarettes. The rest I just wasted"

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                            • #15
                              Re: Compression test fail

                              Originally posted by Steve TLS View Post


                              Why just stop at rings.
                              OK, I pulled the cylinder covers to both motors and took a couple pics:


                              The above is the suspect motor. It looks like the exhaust valve doesn't seat all the way. I cycled the motor several times and the valve on the left doesn't seat. Then, I did the same on the other motor (the one with a bad gear) and saw:


                              It looks like the exhaust valve is closed on this one. That would explain the compression/lack of power, but not the fuel in the oil.

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