3BN Cylinder

  • 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



  • 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.

  • 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

  • @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 😂

  • @Stevie-Wonder

    Thanks but I will be keeping the 4FU.

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

  • 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).

  • 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.

  • @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?


  • 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)

  • @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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