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DT125R FORUM

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  4. Cylinder head O ring conversion

Cylinder head O ring conversion

Scheduled Pinned Locked Moved Engine
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  • CalumC Calum

    @moggy74 I can't comment on YZ or DT conversions I've not done it myself.

    The Aprilia RS 125 uses O-Rings and I had a cylinder lying around. 1.50mm

    alt text

    M Offline
    M Offline
    mhbikesnbits
    wrote on last edited by
    #3

    @Calum what thickness oring

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    • M Offline
      M Offline
      mhbikesnbits
      wrote on last edited by
      #4

      Could try this calculator, do some more research and go for most logical one worst comes to the worst could use a thicker of thinner oring

      https://ceetak.com/o-ring-calculator

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      • Stevie WonderS Offline
        Stevie WonderS Offline
        Stevie Wonder
        wrote on last edited by
        #5

        @moggy74 said in Cylinder head O ring conversion:

        I'm doing an O ring conversion on a 3MB 'p' cylinder head. I have the YZ o ring which is 1.7 mm thick. A general engineering shop is cutting the grove but is asking how deep the grove needs to be. Any advice appreciated

        I think PJME other this service for DT heads as quite a lot of people struggle with head gasket problems + they can be expensive in comparison to an O ring.

        The reason I mention is PJME also provide the o-rings.

        Either get into touch with them or find a suitable O-ring for the application / size and measure it as you’ll only ever replace one o ring for another, not like you’ll need different sizes

        CalumC 1 Reply Last reply
        1
        • Stevie WonderS Stevie Wonder

          @moggy74 said in Cylinder head O ring conversion:

          I'm doing an O ring conversion on a 3MB 'p' cylinder head. I have the YZ o ring which is 1.7 mm thick. A general engineering shop is cutting the grove but is asking how deep the grove needs to be. Any advice appreciated

          I think PJME other this service for DT heads as quite a lot of people struggle with head gasket problems + they can be expensive in comparison to an O ring.

          The reason I mention is PJME also provide the o-rings.

          Either get into touch with them or find a suitable O-ring for the application / size and measure it as you’ll only ever replace one o ring for another, not like you’ll need different sizes

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

          @Stevie-Wonder That's interesting, in the 12 years I've had my DT I've never had head gasket issues. The only person I know to have problems is @SpookDog 🤣

          I assumed it was so they can run higher compression and therefore more power.

          Always Originate, Never Pirate!

          Stevie WonderS HOTSHOT IIIH 2 Replies Last reply
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          • CalumC Calum

            @Stevie-Wonder That's interesting, in the 12 years I've had my DT I've never had head gasket issues. The only person I know to have problems is @SpookDog 🤣

            I assumed it was so they can run higher compression and therefore more power.

            Stevie WonderS Offline
            Stevie WonderS Offline
            Stevie Wonder
            wrote on last edited by Stevie Wonder
            #7

            @Calum Me either bud, so I can’t personally attest. Over the years though I have seemed this be a frequent issue although I’m pretty certain most of the time that’s caused by cheap gaskets or uneven mating surfaces

            Poor @SpookDog too 😂

            Regardless £50 for a gasket Vs £5 for some O-rings + the added benefits that come with it isn’t bad shout

            CalumC 1 Reply Last reply
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            • Stevie WonderS Stevie Wonder

              @Calum Me either bud, so I can’t personally attest. Over the years though I have seemed this be a frequent issue although I’m pretty certain most of the time that’s caused by cheap gaskets or uneven mating surfaces

              Poor @SpookDog too 😂

              Regardless £50 for a gasket Vs £5 for some O-rings + the added benefits that come with it isn’t bad shout

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

              @Stevie-Wonder Yeah, especially as OEM gaskets rise in price and get harder to obtain, it's certainly worth considering. And again, if it does raise compression for more power 👍

              Always Originate, Never Pirate!

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              • M moggy74

                I'm doing an O ring conversion on a 3MB 'p' cylinder head. I have the YZ o ring which is 1.7 mm thick. A general engineering shop is cutting the grove but is asking how deep the grove needs to be. Any advice appreciated

                MadGyverM Offline
                MadGyverM Offline
                MadGyver
                wrote on last edited by MadGyver
                #9

                @moggy74 said in Cylinder head O ring conversion:

                I'm doing an O ring conversion on a 3MB 'p' cylinder head. I have the YZ o ring which is 1.7 mm thick. A general engineering shop is cutting the grove but is asking how deep the grove needs to be. Any advice appreciated

                Did you try a custom copper headgasket,less hassle,reusable and is used in high compression/performance. In a DT does perfect the job.

                I need my tools and a pile of junk.....

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                • CalumC Calum

                  @Stevie-Wonder That's interesting, in the 12 years I've had my DT I've never had head gasket issues. The only person I know to have problems is @SpookDog 🤣

                  I assumed it was so they can run higher compression and therefore more power.

                  HOTSHOT IIIH Offline
                  HOTSHOT IIIH Offline
                  HOTSHOT III
                  wrote on last edited by HOTSHOT III
                  #10

                  @Calum said in Cylinder head O ring conversion:

                  @Stevie-Wonder That's interesting, in the 12 years I've had my DT I've never had head gasket issues. The only person I know to have problems is @SpookDog 🤣

                  I assumed it was so they can run higher compression and therefore more power.

                  I never had a DTR headgasket leak when I was younger but I've had two fail this year; one on my 12,000 mile '93 which I'm fairly certain had never been stripped (I bought it completely original at 6k and the bore is standard) and a '98 French import with 60,000 km, the highest mileage DTR ever sold by Unit 5. And when I stripped it it was still on the standard bore as well!

                  I guess the previous owner must have had so many rebuilds they ended up having to buy a new cylinder, I know they used it to commute in and out of Paris every day for over 10 years so maybe it's just age/wear on both counts if they racked up some of those miles on the new cylinder. Certainly seemed OK after I replaced it and lapped in the cyl head.

                  I didn't know PJME offered the O-ring prep service, might be interested in that.

                  CalumC 1 Reply Last reply
                  1
                  • HOTSHOT IIIH HOTSHOT III

                    @Calum said in Cylinder head O ring conversion:

                    @Stevie-Wonder That's interesting, in the 12 years I've had my DT I've never had head gasket issues. The only person I know to have problems is @SpookDog 🤣

                    I assumed it was so they can run higher compression and therefore more power.

                    I never had a DTR headgasket leak when I was younger but I've had two fail this year; one on my 12,000 mile '93 which I'm fairly certain had never been stripped (I bought it completely original at 6k and the bore is standard) and a '98 French import with 60,000 km, the highest mileage DTR ever sold by Unit 5. And when I stripped it it was still on the standard bore as well!

                    I guess the previous owner must have had so many rebuilds they ended up having to buy a new cylinder, I know they used it to commute in and out of Paris every day for over 10 years so maybe it's just age/wear on both counts if they racked up some of those miles on the new cylinder. Certainly seemed OK after I replaced it and lapped in the cyl head.

                    I didn't know PJME offered the O-ring prep service, might be interested in that.

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

                    @HOTSHOT-III They certainly don't last forever, can't recall the service intervals but it should be rings at 7k miles which means new gaskets etc.

                    But I've heard stories of people running 30k km on original everything lol.

                    Always Originate, Never Pirate!

                    S 1 Reply Last reply
                    1
                    • CalumC Calum

                      @HOTSHOT-III They certainly don't last forever, can't recall the service intervals but it should be rings at 7k miles which means new gaskets etc.

                      But I've heard stories of people running 30k km on original everything lol.

                      S Offline
                      S Offline
                      SpookDog
                      wrote on last edited by
                      #12

                      I know it’s an old thread, but: It’s the barrel that gets grooved, not the head (I thought it was head as well) and it is £35 @ PJME according to the email they sent me 👍

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