difference between 3BN and 3MB head



  • hi. i am guite new here and new with DT. i have read somewhere that 3BN head is restricted. can anyone tell me how is 3BN diferent from 3MB head and how can be derestricted if possible. thanks



  • The 3BN head has a combustion ring around the combustion chamber. Disrupting the combustion flow.

    The 3MB head does not have this ring.

    Grind out the ring, correct the squish band and have the compression corrected and it'll be just as good, if not better, than a 3mb. Mick Abbey ported my 3MB head for £30. So I'd imagine he'd be able to derestrict a 3BN for around the same price.



  • thanks for info but i am new into this so if you can show photos will be great.
    p.s. i am not from uk and my place dont have lot of DTs and i have to do all by my self. thanks again



  • I did have a photo but I am not at that PC ATM. I am sure someone will be along shortly.



  • 0_1483566895065_DT125RHeads diffrences.jpg



  • thanks for the photo. i just need to grind off the ring. what compresion should i get then. the bike has new top end
    thanks



  • @dtr-mkd No, simply just no.

    Did you not read my response bud. The Squishband is critical in getting performance out of a two stroke. A high percentage of power can be made or loss at the head.

    Seriously bud, if you don't know what you are doing then get a specialist to do it.



  • just spoke with Mick Abbey and he charges £35 to do a 3bn head money well spent



  • @Calum thanks calum but as i said i am not from uk and not specialist near me at all so i will have to figure it out by myself. now i have to learn about Squishband. are there any measurements about that. thanks anyway and i forgot: happy new year 🙂



  • @dtr-mkd I'd suggest buying Graham Bell's Two Stroke Performance Tuning. That book would contain everything you would possibly need to know about building a two stroke motor, including modifications to the head.



  • I wouldnt bother, the performance between the 2 alone should be hardly noticable... You still wont win any dragraces... 🙂



  • @Jens-Eskildsen I beg to differ. As said, most of the power of a two stroke can be found in the cylinder head. It's well worth investing money into the head.

    As said, don't take my word for it, read that book.

    The head alone won't win races, but it's a really good place to start, other mods like exhaust, jetting and intake will see noticeable gains.

    Although the single one thing I'd recommend over anything else is a custom ignition.



  • @Calum said in difference between 3BN and 3MB head:

    @Jens-Eskildsen I beg to differ. As said, most of the power of a two stroke can be found in the cylinder head. It's well worth investing money into the head.

    As a genral rule yes, but this was specific between the 2 heads listed by the PO.
    Heck, some people even tried and had a hard time noticing any difference.

    So I still stand by my comment, I dont think its worth the cost for us foreigners who cant just get a head fixed for 35 quid. Most shops here charge you about 35 quid for just walking in to the shop. I think a normal skimjob is more than 35 here in Denmark. Let alone any custom work.



  • my reprofiled 3BN head by mick abbey tuning is done and looks great just need to get it back and fitted now 0_1484252329973_3bn head reprofiled.jpg



  • @britshgigolo Nice one mate that looks a million.times better



  • cant wait to get it to try it out as got new cylinder waiting to go on as well



  • Grind out the ring, correct the squish band and have the compression corrected and it'll be just as good, if not better,

    What do you mean by ''correct the sqish band''..what a sqish band ?
    And how do you correct the compression bud ?



  • @scotty Correct the compression is simply getting the compression ratio back to how Yamaha specify it.

    The Squishband determines how the combustible mix is compressed.

    I suggest if you really want to know more that you perhaps read a book on the subject. I would be lying if I said I know what to do, it's a tuners job. I would suggest Graham Bell's Two Stroke Performance Tuning as a good book.



  • @Calum cheers mate,I'll look out for that book