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  1. #1

    Default M Series Engines

    I have an '84 Chevy K20 with the "M" series engine in it that I want to rebuild. The "M" designation indicates "heavy duty" but what does this really mean with that designation? I've heard it deals with the heavy duty CA smog or it has a higher torque rating or that it has a 4-bolt main with a higher nickel content in the block. Does anyone know for sure?

  2. #2


    I can't help you here either. Sometimes heavy duty is referred to towing so maybe the engine has a camshaft and setup the favors towing better than a normal motor.

    2006 Duramax LBZ
    Edge Evo
    4'' Diamond eye to 6'' tip
    16'' ion alloy, 33'' fierce attitudes
    Lots of work left to do!

  3. #3


    That is correct...the M is in the VIN. I have talked to my local Chevy dealer and they aren't sure either...which I thought was odd but then again.

  4. #4

    mfleetwood's Avatar
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    Jul 2010
    Denver, CO
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    I believe the "M" indicates that your engine or vehicle was made in Michigan or that it is a 5.0 liter/V-8. Check out this link as I think it will help solve the rest of your mystery.

    Mike (Denver, CO) - 2008 Sierra 1500 Z71 SLE 5.3L 4WD

    SUSPENSION: Rancho 4" Suspension Lift; Rancho RS9000XL Shocks; Rancho Skid Plates; Rancho MyRide Wireless Shock Controller;
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  5. #5


    My '85 Chevy G30 van has a "L" digit engine, as opposed to your "M", and that it stands for light duty - though I still don't know what the difference is between the two.

    Conversely, my old '75 Jimmy engine is a "J" code, which is stamped on the block, and I was told that stood for high nickel. It is a four bolt, and a torquee SOB.

    Are you just curious about the engine, or are you trying to find parts?

    Welcome aboard, and good luck.

    1999 Chevy K2500 Suburban 350
    K&N, reworked cai, Thrush cat-backs
    Vinyl, cranks, floor shift, and rear air!

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