4. DT125X replacement head question

DT125X replacement head question

  • W

    Hi all,

    I need to replace the cylinder head on my dt125x and am unsure about a few things -

    Will any 3BN head fit?
    What does the 'Y' number on the head indicate?
    Is there a certain one that can give better performance over stock?
    Are there any big no-no's when choosing a 2nd hand head?

    Thanks in advance 🙂

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  • Global Moderator

    I found out when buying my replacement head that the Y number is virtually irrelevant. Someone mentioned to me a while back it was to do with the mould / tools they use at the factory and doesn't represent any differences with the heads themselves.

    You can definitely get ones that provide better performance than the stock 3BN one but the best route for that would be to purchase a stock one and send it off to be properly ported.

    1

  • If your looking to replace the Cylinder head, a Y--1 3MB was the later head Yamaha produced for the DT125RE/X

    It has no restrictive Combustion ring like a 3BN. Will run a little better.

    Any 3BN will fit.

    When looking for a head, look for ones that have been skimmed properly, or just of low mileage. Unfortunately difficult to check warping buying over the net.

    1

  • As the lads have right said. 3BN fits but has a restictor, combustion ring, on it which is not good.

    Avoid heads with pitting as they are no good. You want a nice head that has no pitting. If its sooty it can be polished but it's actually a known fact that sooty heads can actually increase performance, at the risk of reliability.

    The soot acts as an insulator in the combustion chamber. Higher temps result in faster moving aor molecules. This gives a greater thrust onto the piston. But the excess heat can lead the engine into detonation, amongst other issues.

    Personally, fascinating subject.

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