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M42 valve seat specs

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    M42 valve seat specs

    Hi to all of you! :) My name's Matteo.
    I kindly need some information about M42 valve seat job.

    My head suffered from crack in cylinder 2, from water passage to exhaust valve seat.
    Also in cylinder 3 there's a crack between exhaust valves.

    I have to cut it and weld. Then remake valve seat.

    Some information:
    Valve seat width

    Intake mm 1.65 ± 0.25

    Exhaust mm 2.0 ± 0.25

    Ø valve seat

    Intake, outer Ø mm 32.4

    Exhaust, outer Ø mm 30.1

    Ø valve diameter
    Intake 33 mm

    Exhaust 30.5 mm

    I can proceed with valve cutters, but I need confirm. Which diameter of valve cutter should I use for intake and exhaust valve seat? Angle for both is 45 deg.
    Maybe addressing this question to those who already have done this.

    Many thanks.

    Just get good used head, instead. "Passion is timeless"
    '91 318i (Alpine) - daily
    '88 325ix (Zinno) - drive here and there!


      Repairing the cracked head is not likely to give a good long term solution since the cracks go all the way through, and a weld will penetrate only part of the depth. As fresh_td said, finding a good used head will provide much better results. These engines do not like to overheat, which is probably the cause in most cases, but I also suspect that maybe there were some issues with quality control during production (maybe a defect in one of the molds) since some heads seem to crack very easily, and some seem to have no problems ever.