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M40 Cam Belt Replacement

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    M40 Cam Belt Replacement

    I have an M40B18. The cam belt was last replaced in December 2017 at 222448 km. The car has now done 229343 km. So, that is 5 years and 6895 km. Should I be concerned about it and have it replaced soon due to the long time it has been in use, or is it unlikely to be worn out due to the short distance that it has traveled?
    1990 318i 4-door, 5 speed manual, ice white

    #2
    IIRC, M20s have a suggested interval of 60k miles or 4/5 years, so I'd bet that M40s are the same. On mine I also replaced it in late 2017, and it's been about 30k KM. I also a new kit last week, and I expect the one I take off to look perfect, but it's much easier to do a timing belt than an engine replacement.

    Basically, it could be good for decades, or it could fail tomorrow, which is why there is a time and a mileage based interval, which should be well within safety margins since most manufacturers probably expect people to overrun maintenance intervals.

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      #3
      Originally posted by roguetoaster View Post
      IIRC, M20s have a suggested interval of 60k miles or 4/5 years, so I'd bet that M40s are the same. On mine I also replaced it in late 2017, and it's been about 30k KM. I also a new kit last week, and I expect the one I take off to look perfect, but it's much easier to do a timing belt than an engine replacement.

      Basically, it could be good for decades, or it could fail tomorrow, which is why there is a time and a mileage based interval, which should be well within safety margins since most manufacturers probably expect people to overrun maintenance intervals.
      Thank you for your response. The M40 cam belt recommended replacement interval is half that of the M20. So, time-wise mine is now way overdue. I will make arrangements to have it replaced, and avoid using the car very much until then.
      1990 318i 4-door, 5 speed manual, ice white

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        #4
        That interval seems somewhat excessive, but it won't hurt anything to change it early relative to other timing belt intervals.

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          #5
          I have seen reports that M40's are harder on Timing Belts.

          I don't understand why, but the penalties for one failing are high.

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            #6
            Originally posted by twright View Post
            I have seen reports that M40's are harder on Timing Belts.

            I don't understand why, but the penalties for one failing are high.
            The other way to look at it is that when your otherwise perfectly functional M40 dies you have a real reason to swap in a more modern twin cam six.

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