3bn Y-1.......3bn Y-3



  • Does anyone know the differences between these 2 different heads? Please shed some light... been online looking for some time now and cant tell..

    I can see the that one has "fins" o the bit below where it says y-1/3

    See pictures below(if ii get this upload right!)

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  • What is the difference from underneath, do they both have the restriction ring on the chamber?

    The 3BN is inferior to the 3MB regardless, so I would be on the lookout for a 3MB head, or have that nasty combustion ring removed.



  • Yeah i have been reading an older post of yours regards the combustion ring... i have these two, so which ever is superior will send for machining. Im going to have to look again because i cant remember who was recommended.

    Once i take off the head that's currently on the motor i will update with internal information...
    The other difference i can see is the banjo screw location on the thermostat housing.



  • @calum 3bn 3mb.... is there a superior barrel ?

    As under inspection of the pics i took today... and i have a 3bn head (x2) and a 3mb barrel!



  • I guess I'm more familiar with Y-3. At a guess, it's just an early head. Either way they're not the best heads,

    Yeah the common barrels are 3MB. The older barrels 1988 I believe are 3BN barrels. Slightly shorter stroke, bigger bore, and the last heads were 3MB.

    3MB Barrel with 3MB head would be a pretty sweet deal if you can get it.



  • The y1 has had a slight rub with some wet dry multiple stages of grit mounted to a glass panel.

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  • @dt125matt A favourite trick of mine lol.

    But really that combustion ring needs milling out and the squish band altered to be any good. A competent porter will do it for £35 Sterlin. I had a 3MB head done for that much.



  • Do you have any trusted porters ? Or machineists?
    I like in harrow (london) or watford....

    Im looking for sandblast/powder coaters
    A rebore with new sleeve and forged piston
    And porting/polishing



  • @dt125matt No, I mean I used Mick Abbey to get my cylinder done. Can't really comment on how it fairs to stock, since I did loads of mods and didn't really notice much...