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DT125R FORUM

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  2. Tuning
  3. Top End
  4. 3BN Cylinder

3BN Cylinder

Scheduled Pinned Locked Moved Top End
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  • R Offline
    R Offline
    rubberfingers
    wrote on last edited by
    #1

    Hello

    One of my DT's is a 1988 with the early crank, the stroke is shorter at 50.0 vs 50.7 for the later bikes. It however has a 4FU top end which has been fitted without a base gasket (case sealant instead) to correct the stroke.

    It goes well but it always niggles me that it does not have the correct top end vs crank and could have slightly off port timing as a result.

    Does anyone have a (mostly useless to anyone else!) 3BN cylinder and PV they dont need I could buy? I have also seen some photos of DT's fitted with a 2RH top end from a TZR (which has the same bore/stroke as the 88 dt). Can anyone confirm if these are a direct swap, does the lower cylinder bore match the DT cases?

    I could swap out the crank but its a lot of effort for not much gain (if any)

    Any help or knowledge on this is appreciated

    cheers

    Andy

    2 Strokes
    RD500 TDR250 TZR250 2MA TZR250 3MA DT125RE DT125R TS125

    4 Strokes
    YZF600R XS750 FZ1

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    • O Offline
      O Offline
      oldman
      wrote on last edited by
      #2

      Still pop up time to time on eBay, I picked up 2 in a few months. My original barrel was near end of rebore possibilities, one was used on rebuild and have kept the other for spares.

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      • A Offline
        A Offline
        Arild
        wrote on last edited by
        #3

        Hey mate, i got a 1988 bike and i have the 3bn barrel on it, if u wanna swap the 4fu for the 3bn id be down mate

        Stevie WonderS 1 Reply Last reply
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        • A Arild

          Hey mate, i got a 1988 bike and i have the 3bn barrel on it, if u wanna swap the 4fu for the 3bn id be down mate

          Stevie WonderS Offline
          Stevie WonderS Offline
          Stevie Wonder
          wrote on last edited by
          #4

          @Arild said in 3BN Cylinder:

          Hey mate, i got a 1988 bike and i have the 3bn barrel on it, if u wanna swap the 4fu for the 3bn id be down mate

          Cheeky 😂

          R 1 Reply Last reply
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          • Stevie WonderS Stevie Wonder

            @Arild said in 3BN Cylinder:

            Hey mate, i got a 1988 bike and i have the 3bn barrel on it, if u wanna swap the 4fu for the 3bn id be down mate

            Cheeky 😂

            R Offline
            R Offline
            rubberfingers
            wrote on last edited by
            #5

            @Stevie-Wonder

            Thanks but I will be keeping the 4FU.

            Does anyone have knowledge on the 2RH top end fitting?

            2 Strokes
            RD500 TDR250 TZR250 2MA TZR250 3MA DT125RE DT125R TS125

            4 Strokes
            YZF600R XS750 FZ1

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

              No, as far as I'm aware, only the Belgarda models had any sort of compatibility with the DTR. So the European Belgarda (4FU) and the Italian (3MB00P).

              Always Originate, Never Pirate!

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              • MadGyverM Offline
                MadGyverM Offline
                MadGyver
                wrote on last edited by
                #7

                It matches crankcases without modification and will fit only with the cylinder head already bolt on and LOT of patience,because of the bigger head,longer studs and tighter space.
                Custom cylinder brackets required,and little repositioning of the radiator hoses and coil.

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

                R 1 Reply Last reply
                1
                • MadGyverM MadGyver

                  It matches crankcases without modification and will fit only with the cylinder head already bolt on and LOT of patience,because of the bigger head,longer studs and tighter space.
                  Custom cylinder brackets required,and little repositioning of the radiator hoses and coil.

                  R Offline
                  R Offline
                  rubberfingers
                  wrote on last edited by
                  #8

                  @MadGyver Many thanks for the info. I think I will see if I can get a 3bn cylinder.

                  Is the pv the same as a 3mb?

                  Thanks

                  2 Strokes
                  RD500 TDR250 TZR250 2MA TZR250 3MA DT125RE DT125R TS125

                  4 Strokes
                  YZF600R XS750 FZ1

                  NottsbikerN 1 Reply Last reply
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                  • NottsbikerN Offline
                    NottsbikerN Offline
                    Nottsbiker
                    wrote on last edited by
                    #9

                    Should be plenty of Belgarda stuff kicking around in France / Italy etc

                    Cant see it making much difference to be honest, you'd be better with a tuned 170 kit or a 200 cylinder of some sort (200R or 200WR)

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                    • R rubberfingers

                      @MadGyver Many thanks for the info. I think I will see if I can get a 3bn cylinder.

                      Is the pv the same as a 3mb?

                      Thanks

                      NottsbikerN Offline
                      NottsbikerN Offline
                      Nottsbiker
                      wrote on last edited by
                      #10

                      @rubberfingers

                      Some have a diamond shape on the pulley end but they all take the same pulley - worth noting so that when setting up you get it the right way round. Best thing thing to do would be to feel up the port with the exhaust off.

                      I have both a 3SH TDR125 and a 3XP 200WR if you need any info - both engines are in one piece though so cant comment on the internals right now 😉

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