3bn/3mb barrel differences



  • Can anyone confirm weather or not the 3bn and 3mb barrels are the same or not please. I understand from factory they have different bore sizes but this wouldn't matter seings they're all been rebored by this time. Are there any other differences?

    Yes I no the heads are different before anyone says it. I'm asking about BARRELS lol thanks



  • Doesn't work like that mate.

    Because the bores are different out the factory, it means the strokes are different in order for the displacement to be kept the same.

    The engine that came with the 3BN cylinder also came with a slightly shorter stroke. Therefore you will have to space out the base gasket in order to get it to fit. Then rework the squish band.

    It is possible however. A chap many moons ago done it. You will gain a few cc's so it willneed jetting accordingly.



  • Ok cool thanks. My Dt is a 1990 full power one. It has a 3mb barrel. Do you no if this is the right one fitted for the year? Thanks



  • Does this have something to do with the markings "3MB 00" or "3MB 0" on the cylinder? I see that it matters when you order con rod kit from PJME.



  • Yes they are diffrent! I brough the dt125r 99 ypvs from a lad that had just put in a new jesil race crank in and sold it to me as just needs new head gasket, so popped one in and bang it went! i then groved a ring around the bore of the head and poped a Heat rated orange o ring in with this heat rated glue stuff! It worked i then put and standard exhaust in down jetted from 240 to 210, not long after it blows up 4 miles from home 2300 long walk home, so i brough a copper gasket same again. 2 base gaskets (lowers the compression) ive read on here? Same as then saw this and checked mine 3mb00 barrell and 3mb head, looked on ebay to see if yama sold a 3mb head and it is very diffrent! like is Has got an little adge around the bore giving better hold of the compression than a 3bn that is complely flat, my question is can i still use my copper gasket or go for the standard one what also has the imprint of the little adge around the bore? And a thank you i wouldnt have figured it out without this page!!! 🙂