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  • #46
    Reckon you could get him to elaborate on that last sentence mate? Sounds like he's suggesting that when it gets quite hot it's letting a little coolant in? Does he have any suggested ways to test for / correct this?
    Charlie
    06 ktm300

    Comment


    • #47
      Sure, I'll GBTYS.
      I love GREEN

      ^roost '98 KDX/KX 200 Hybrid "Tweaked by Terry" ^roost


      Some people are like slinkys, good for nothing really but you still get a laugh pushing em down the stairs...

      The day Microsoft makes something that doesn't suck is probably the day they
      start making vacuum cleaners.

      Windows95 is a 32-bit extension to a 16-bit shell of an 8-bit O/S originally
      written for a 4-bit microprocessor by a 2-bit company that can't stand 1-bit of competition.

      Club Mud #147

      Comment


      • #48
        Some food for thought.

        Pressure testing is good for identifying a number of problems with leakage - both intake type and pressure lost leakage. On a head coolant seepage problem it may or may not help identify the root of the problem.

        There of course a number of possible factors like head warpage, bad O-Ring, foreign matter, etc which can be the cause of the problem. On KTMs, in particular, the bolt fasteners used on the head can contribute to problems of this nature and are generally over looked, or not understood, by many shops performing maintainance work.

        If a head bolt(s) has been tightened beyond its yield strength (even once) then the bolts will permanently loose its ability to hold constant tension between the cylinder head and the cylinder even though the head bolt is "tight". Sound confusing???

        Different metals and different alloys expand/contract at different rates depending upon a variety of factors. The purpose of the head bolts is to keep relative constant tension/pressure on the gasket or mating surface between he head and the cylinder. As the cylinder heats-up it grows in length. This is at a slightly different rate than the head which is also growing in all three dimensions as it heats up. As the components cool contraction of the materials also take place.

        There will generally be a difference in temperature which is always changing between the mated components due to engine load, stream crossings, natural cooling, coolant flow, etc.

        Torquing head bolts is designed to stretch the bolts WITHIN A GIVEN LIMIT ( while remaining in the yield strength range for the bolt). This allows the head to be held to the cylinder within a prescribed range of tension. This allows for sealing of the combustion chamber, coolant flow passages, etc.

        Summary - If the head bolt has been stretched beyond the bolt's material yield strength (elastic property) the bolt's molecular structure has been changed and the bolt has lost it elasticity. This elastic property of the head bolts is what works in conjugation with the gaskets/O-Ring to keep the engine sealed.

        P.S. Ever been tightening a bolt and feel it "give" and you just know be experience that another little nudge will result in a broken bolt? If you have experienced the aforementioned then you have reached or exceeded the "tensile" strength of the bolt. The bolt is elongating/stretching and being pulled apart or tensile failure. The yield strength is usually somewhere in the range of 60-70% of the tensile strength and you cannot "feel" it when it is exceeded.

        BOTTOM LINE -The head bolt can still be tightened down to a prescribed torque value and not function as intended. It will be "tight" when torqued down but will not 'grow and contract' with the temperature changes as originally intended by the engine designer. This can lead to coolant seepage, failure of sealing gaskets, etc.
        I love GREEN

        ^roost '98 KDX/KX 200 Hybrid "Tweaked by Terry" ^roost


        Some people are like slinkys, good for nothing really but you still get a laugh pushing em down the stairs...

        The day Microsoft makes something that doesn't suck is probably the day they
        start making vacuum cleaners.

        Windows95 is a 32-bit extension to a 16-bit shell of an 8-bit O/S originally
        written for a 4-bit microprocessor by a 2-bit company that can't stand 1-bit of competition.

        Club Mud #147

        Comment


        • #49
          Might be a good idea to get some new head studs. Shouldn't be too dear and at the worst you can eliminate them causing the issue. Hope the info helps some and good luck...
          I love GREEN

          ^roost '98 KDX/KX 200 Hybrid "Tweaked by Terry" ^roost


          Some people are like slinkys, good for nothing really but you still get a laugh pushing em down the stairs...

          The day Microsoft makes something that doesn't suck is probably the day they
          start making vacuum cleaners.

          Windows95 is a 32-bit extension to a 16-bit shell of an 8-bit O/S originally
          written for a 4-bit microprocessor by a 2-bit company that can't stand 1-bit of competition.

          Club Mud #147

          Comment


          • #50
            Thanks for the info KDXer - I got some new bolts and torqued them up yesterday.
            Charlie
            06 ktm300

            Comment


            • #51
              Would be very interested to hear the cause if/when you find one.
              I love GREEN

              ^roost '98 KDX/KX 200 Hybrid "Tweaked by Terry" ^roost


              Some people are like slinkys, good for nothing really but you still get a laugh pushing em down the stairs...

              The day Microsoft makes something that doesn't suck is probably the day they
              start making vacuum cleaners.

              Windows95 is a 32-bit extension to a 16-bit shell of an 8-bit O/S originally
              written for a 4-bit microprocessor by a 2-bit company that can't stand 1-bit of competition.

              Club Mud #147

              Comment


              • #52
                Pulling the head off a ktm 150 at 24hrs which is trailriden only.
                Are there any experienced engine builders out there that can comment and what are people's thoughts on this and the way it is running?
                95 fuel,motorex 2t oil at 40:1
                The rider is young and feedback is hard to gather. As long as it starts and runs they just ride.

                Comment


                • #53
                  As the 150 head is the 2 piece insert design and can sit in any position,is there any prefered sparkplug electrode orientation for a 2 stroke motor? ie across, towards back or front. I remember when we were boat ski racing the mechanic used to index plugs a certain way.

                  The oem position when i pulled it apart was with the electrode facing across the motor.

                  Comment


                  • #54
                    Originally posted by cluffie View Post
                    As the 150 head is the 2 piece insert design and can sit in any position,is there any prefered sparkplug electrode orientation for a 2 stroke motor? ie across, towards back or front.
                    The open end of the plugs' earthing arm should point to centre of the rear boost port. On road racing 80s and 125s I index plugs. For everything else it doesn't matter.

                    That head has too much SC Cluffie, it should be 1.00-1.05mm. Worth a check. Can't wait for mine to arrive...
                    "Mindfulness has no interest in knowing the answers, it exists solely in understanding the questions"

                    Comment


                    • #55
                      Cluffie, for reference here is an old pic of the piston top when I did a top end at 75 hours on my 2013 KTM 150. Same as you, 40:1, well jetted, Dave did some minor cylinder mods and set the Squish at .95, about 10psi more than standard. It was a good motor

                      I sold it to my neighbours teenagers who are still riding it.

                      Nutty, That's interesting about the rear boost port. Some years ago I read about indexing plugs and ever since I try to put the open end East/West but often it doesn't line up. Let us know how the new 150 goes. There are still some small bore fans around.

                      Cluffie, is that two piece head an aftermarket item?
                      Attached Files
                      Current: 250 & 125 2T & 250 4T

                      Comment


                      • #56
                        Specs for interest
                        Attached Files
                        Current: 250 & 125 2T & 250 4T

                        Comment


                        • #57
                          Thanks guys. As for indexing Nutty, i thought it was as you said. As the head is 2 piece it's easy to screw the plug into the head while it is off and see where the electrode ends up. Then mark it with a texta and put the head insert in to suit. i'll set it up towards the rear boost port.

                          Riles,stock head. The plugs vary a bit and i had 3 spare plugs so i screwed them all into the head to see where the electrode ended up. 2 plugs were the same and one was different so i now have a spare plug that will line up to the rear boost port.
                          On a 300 i wouldn't worry about this but as it's a smallbore and 2 piece head why not it's so easy.
                          75hrs for a piston is exceptional Riles. Did you do rings before 75hrs and were you happy with this amount on hrs or would you change the service interval?

                          Comment


                          • #58
                            Cluffie, i think 75hrs was the first top end. No rings before that. I kept a check on compression, the next one was at about the same hours. The neighbour I sold it to came back last year and said can I do a top end for him which I did, it had done 80+. Bottom end is still fine, so is the cylinder and the ring gap always measures about the same so I am not going to do them before 75 hours now. Everyone has their opinion on top ends but I'm giving you my 150 experience since you asked.
                            Current: 250 & 125 2T & 250 4T

                            Comment


                            • #59
                              Thanks Riles, 75-80hrs sounds safe from your experience. I'll keep an eye on it and do some comp. testing up until then.

                              Comment


                              • #60
                                I think the clean areas of the piston indicate there is lots of fuel/air mixture flow over it from the transfers and/or boost. Ideally the direction of the clean areas should be rearward. If one side of the piston is cleaner than the other then the transfers aren't opening equally.

                                Comment

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