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DT125R FORUM

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  4. Head gasket

Head gasket

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  • P Offline
    P Offline
    Pilot_LC
    wrote last edited by
    #1

    Hello
    So i have a problem my cylinder head is slightly scratched and a little bent so the regular metal gasket doesnt seal it (coolant gets in the bore) but i found a solution a athena composite head gasket that nicely squished the head together but it was time for a rebuild and i had to tear it down tried to fit a normal headgasket but that didnt hold (found out the hard way) so im in need of the thicker athena composite headgasket but i cant find it anywhere and i cant remember what store i bought it from.

    Thanks for any help!

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    • P Offline
      P Offline
      Pilot_LC
      wrote last edited by
      #2

      forgot to add the part where i ask for help if anyone knows where to get one 🙂

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      • CalumC Offline
        CalumC Offline
        Calum
        wrote last edited by
        #3

        Several options

        Can you not skim the head and barrel and remove the imperfections, then space the barrel with two bottom gaskets?

        Can you not get yourself a reusable copper head gaaket. They used to be all the range a few years ago.

        You could always contact an engineering firm like PJME to machine an o-ring into your setup to bypass the imperfections.

        https://www.pjme.co.uk/acatalog/Yamaha-DT125R-Head-Gasket-O-Ring--5866.html

        Always Originate, Never Pirate!

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        • P Offline
          P Offline
          Pilot_LC
          wrote last edited by
          #4

          i sadly cant skim the head because i dont have the machines myself and in my country its a rather ellusive and expensive thing
          where could i find the copper gasket and will it make the compression go down?
          and about the o-ring can i let the machining be done at a lathe here by the dimensions on the pjme site and if i switch to o-ring its just the o-ring or is it the o-ring+headgasket

          PS sorry for my spelling english isnt my main language
          and thanks for the help!

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          • P Offline
            P Offline
            Pilot_LC
            wrote last edited by
            #5

            okay found a solution that i completly forgot a large piece of glass + fine wet sandpaper and it should to the trick the cylinder itself is completly fine

            CalumC 1 Reply Last reply
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            • P Pilot_LC

              okay found a solution that i completly forgot a large piece of glass + fine wet sandpaper and it should to the trick the cylinder itself is completly fine

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

              @Pilot_LC Yeah, I wrote a blog on doing it here: https://dt125r.co.uk/post/23

              It's only a gentle skim, it won't cure completely warped heads.

              Be sure to the deck of the barrel too.

              Always Originate, Never Pirate!

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              • P Offline
                P Offline
                Pilot_LC
                wrote last edited by
                #7

                did the process the original gap was about 0,1mm got it down to zero put it together with a new standard gasket and it holds! also it has more compression now then ever before and i can feel that it has more power

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

                  @pilot_lc That's amazing! Fingers crossed 🤞 that's it now then.

                  Always Originate, Never Pirate!

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                  • P Offline
                    P Offline
                    Pilot_LC
                    wrote last edited by
                    #9

                    yeah so it ran for 600km with no problem then started randomly getting really hot and spewing coolant out just like before so now i had to bring it home with a trailer (again) and ill disassemble the head tomorrow to see what the problem is now.

                    CalumC 1 Reply Last reply
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                    • P Pilot_LC

                      yeah so it ran for 600km with no problem then started randomly getting really hot and spewing coolant out just like before so now i had to bring it home with a trailer (again) and ill disassemble the head tomorrow to see what the problem is now.

                      CalumC Offline
                      CalumC Offline
                      Calum
                      wrote last edited by
                      #10

                      @Pilot_LC 600km, are you sure you used a genuine head gasket and not the cheap white ones.

                      And it was definitely fitted in the right orientation.

                      Always Originate, Never Pirate!

                      P 1 Reply Last reply
                      0
                      • CalumC Calum

                        @Pilot_LC 600km, are you sure you used a genuine head gasket and not the cheap white ones.

                        And it was definitely fitted in the right orientation.

                        P Offline
                        P Offline
                        Pilot_LC
                        wrote last edited by
                        #11

                        @Calum yes i used a athena head gasket and its 100% in the right orientation.
                        also what saams to be wierd is that its spewing out coolant from the overflow tank but there is no pressure in the system when you remove the radiator cap even when its really hot. It also doesn't seem to be burning coolant

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                        • CalumC Offline
                          CalumC Offline
                          Calum
                          wrote last edited by
                          #12

                          As I say, one issue is the radiator cap spring looses tension so try replacing that.

                          I just use a cheap Chinese one on my DTR with a temperature sensor in it and it's been sound.

                          Another problem could be the thermostat as given up, maybe it's locked closed so it's not regulating temperature correctly.

                          Always Originate, Never Pirate!

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                          • P Offline
                            P Offline
                            Pilot_LC
                            wrote last edited by
                            #13

                            okay but how would those explain the significant loss of coolant through the overflow tank?

                            CalumC 1 Reply Last reply
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                            • P Pilot_LC

                              okay but how would those explain the significant loss of coolant through the overflow tank?

                              CalumC Offline
                              CalumC Offline
                              Calum
                              wrote last edited by
                              #14

                              @Pilot_LC Ideal Gas Law - PV=nRT. Pressure of a system is directly proportional to the temperature of that system. So if the thermostat is stuck, then the temperature goes up and therefore the pressure. The radiator cap bleeds this pressure to the overflow tank. Ergo explains loss of coolant.

                              Always Originate, Never Pirate!

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