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DT125R FORUM

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Lapping

Scheduled Pinned Locked Moved Top End
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  • BluestoesonnoseB Offline
    BluestoesonnoseB Offline
    Bluestoesonnose
    wrote on last edited by
    #1

    I'm just going through some old RD tuning stuff I followed when I owned a 350LC back in the late 80s, and it suggests deleting the head gasket and lapping the head to the barrels, has anyone tried this with a DT125R motor?

    2002 DT125R

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    0
    • CalumC Offline
      CalumC Offline
      Calum
      wrote on last edited by
      #2

      I doubt you'll get it to seal.

      Back in the Air Cooled days, the engines were cast iron. As such they were less prone to warping. Aluminium will literally just warp.

      The best you can get is a machine O-Ring into the head to eliminate the head gasket. The Rotax engines use these.

      You have to be careful with how much compression you run, pre-ignition and detonation is going to creep in at these sorts of levels and kill your engine.

      Always Originate, Never Pirate!

      1 Reply Last reply
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      • BluestoesonnoseB Offline
        BluestoesonnoseB Offline
        Bluestoesonnose
        wrote on last edited by
        #3

        LC motors are alloy and it seems to be a wide spread practice with the aircooled and watercool boys back in the heydays.

        2002 DT125R

        CalumC 1 Reply Last reply
        0
        • BluestoesonnoseB Bluestoesonnose

          LC motors are alloy and it seems to be a wide spread practice with the aircooled and watercool boys back in the heydays.

          CalumC Offline
          CalumC Offline
          Calum
          wrote on last edited by
          #4

          @Bluestoesonnose I know LC motors are alloy, I was specifically referring to the AC motors since I'd expect this to be where it would work reliably.

          But I've not heard anyone do it to DT's. I guess there must be a reason why it's not so common these days.

          Always Originate, Never Pirate!

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          • BluestoesonnoseB Offline
            BluestoesonnoseB Offline
            Bluestoesonnose
            wrote on last edited by
            #5

            Not totally clear in your reply

            2002 DT125R

            CalumC 1 Reply Last reply
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            • BluestoesonnoseB Bluestoesonnose

              Not totally clear in your reply

              CalumC Offline
              CalumC Offline
              Calum
              wrote on last edited by
              #6

              @Bluestoesonnose I'm not saying it's not possible, I do question it's reliability. O-Ring modification would probably be your best bet. But the discussed factors should be considered.

              Always Originate, Never Pirate!

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              • 2 Offline
                2 Offline
                2stroketerry
                wrote on last edited by
                #7

                The O-ring conversion on a DT 125 using a 90,s YZ 125 O-ring , the tighter squish and less combustion volume really helped. On average I would say this mod gives around 1,0 a 1,5 HP. This will lower the squish from +/-1.35 to a +/-0.95mm
                0_1541544295916_DT.jpg

                CalumC 1 Reply Last reply
                1
                • 2 2stroketerry

                  The O-ring conversion on a DT 125 using a 90,s YZ 125 O-ring , the tighter squish and less combustion volume really helped. On average I would say this mod gives around 1,0 a 1,5 HP. This will lower the squish from +/-1.35 to a +/-0.95mm
                  0_1541544295916_DT.jpg

                  CalumC Offline
                  CalumC Offline
                  Calum
                  wrote on last edited by
                  #8

                  @2stroketerry That looks the tits. Who did that for you?

                  Always Originate, Never Pirate!

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                  • 2 Offline
                    2 Offline
                    2stroketerry
                    wrote on last edited by
                    #9

                    Cost £30 to cut the groove from a machine shop in Southbank
                    0_1541546069494_DT2.jpg

                    declanD 1 Reply Last reply
                    0
                    • 2 2stroketerry

                      Cost £30 to cut the groove from a machine shop in Southbank
                      0_1541546069494_DT2.jpg

                      declanD Offline
                      declanD Offline
                      declan
                      wrote on last edited by
                      #10

                      @2stroketerry I’m surprised you lot like the o rings I hate them with a passion I love the simple metal one like dt has I’m always having leaks and such from poorly fitted o rings even though I try my best to fit them perfectly

                      CalumC 1 Reply Last reply
                      0
                      • declanD declan

                        @2stroketerry I’m surprised you lot like the o rings I hate them with a passion I love the simple metal one like dt has I’m always having leaks and such from poorly fitted o rings even though I try my best to fit them perfectly

                        CalumC Offline
                        CalumC Offline
                        Calum
                        wrote on last edited by
                        #11

                        @declan That's your problem then isn't it. Poorly fitted.

                        I've not had issues with O-Ring gaskets. Usually a dab of grease to hold it in situ is enough to sort any problems out if you're having them.

                        Always Originate, Never Pirate!

                        declanD 1 Reply Last reply
                        0
                        • CalumC Calum

                          @declan That's your problem then isn't it. Poorly fitted.

                          I've not had issues with O-Ring gaskets. Usually a dab of grease to hold it in situ is enough to sort any problems out if you're having them.

                          declanD Offline
                          declanD Offline
                          declan
                          wrote on last edited by
                          #12

                          @Calum none of that worked for me they wouldn’t sit still the last one I did I used the lightest amount of super glue just enough to keep it in the groove and that worked any other time and it would always slip out an pinch the ring I should add this is on the cheap replica rs cylinders so the machining wasn’t exactly flawless

                          1 Reply Last reply
                          0
                          • 2 Offline
                            2 Offline
                            2stroketerry
                            wrote on last edited by
                            #13

                            @declan using glue is the last thing you want on an O-ring just a bit of silicone grease, but having a poorly machined groove the O-ring sits in probably doesn't help.
                            Yamaha use an O-ring on there best 125 cylinders the SP although don't actualy make that cylinder themselves.

                            declanD 1 Reply Last reply
                            0
                            • NINJAN Offline
                              NINJAN Offline
                              NINJA
                              wrote on last edited by NINJA
                              #14

                              I seem to remember someone once said that applying a bit of petroleum jelly, aka the good ole Vaseline works wonders for keeping your 'O' ring in good order.

                              :grinning_face_with_smiling_eyes: :winking_face: :grinning_face_with_smiling_eyes::winking_face: :grinning_face_with_smiling_eyes:

                              SEDUCED BY THE DARK SIDE!!!

                              declanD 1 Reply Last reply
                              1
                              • 2 2stroketerry

                                @declan using glue is the last thing you want on an O-ring just a bit of silicone grease, but having a poorly machined groove the O-ring sits in probably doesn't help.
                                Yamaha use an O-ring on there best 125 cylinders the SP although don't actualy make that cylinder themselves.

                                declanD Offline
                                declanD Offline
                                declan
                                wrote on last edited by
                                #15

                                @2stroketerry the only bike I didn’t have a problem with was a yz 125 that was no issues what so ever

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                                0
                                • NINJAN NINJA

                                  I seem to remember someone once said that applying a bit of petroleum jelly, aka the good ole Vaseline works wonders for keeping your 'O' ring in good order.

                                  :grinning_face_with_smiling_eyes: :winking_face: :grinning_face_with_smiling_eyes::winking_face: :grinning_face_with_smiling_eyes:

                                  declanD Offline
                                  declanD Offline
                                  declan
                                  wrote on last edited by
                                  #16

                                  @NINJA you’d know

                                  NINJAN 1 Reply Last reply
                                  0
                                  • declanD declan

                                    @NINJA you’d know

                                    NINJAN Offline
                                    NINJAN Offline
                                    NINJA
                                    wrote on last edited by
                                    #17

                                    @declan Do not tell me that you did not laugh at that one???

                                    SEDUCED BY THE DARK SIDE!!!

                                    declanD 1 Reply Last reply
                                    0
                                    • NINJAN NINJA

                                      @declan Do not tell me that you did not laugh at that one???

                                      declanD Offline
                                      declanD Offline
                                      declan
                                      wrote on last edited by
                                      #18

                                      @NINJA sorry to say I didn’t i take my o rings very seriously I’m quite anal about o rings

                                      1 Reply Last reply
                                      1
                                      • CalumC Offline
                                        CalumC Offline
                                        Calum
                                        wrote on last edited by
                                        #19

                                        Like with most things, the work is in the preparation.

                                        Always Originate, Never Pirate!

                                        1 Reply Last reply
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