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Technical 8BA heads on 1940 motor pre 59ab

Discussion in 'The Hokey Ass Message Board' started by fryguy, Mar 26, 2021.

  1. fryguy
    Joined: Nov 26, 2005
    Posts: 1,234


    Hey guys I have a flathead question that I havent thought of before. I have a friend that has 1939 block that he's putting in his 39 Coupe. He has a set of 53 Merc EAC heads he wants to throw on the motor. I have never seen anybody want to put the later heads on the early blocks. I have always run the early heads on the late blocks.

    Will this actually work? especially on a pre '42 motor? I hear the valve angles are different on the 38-42 239 blocks from the 59ab blocks.

    Has anybody everydone this before? If so, what modifications if any did you have to do? I assume the 8BA head gaskets will need to be used as well.

    Any experience with this swap?

  2. drtrcrV-8
    Joined: Jan 6, 2013
    Posts: 1,406


    There are a couple of changes required, but I don't remember what. Suggest putting this over on the FORD BARN...
  3. Marty Strode
    Joined: Apr 28, 2011
    Posts: 5,589

    Marty Strode

    I would be more concerned with the differences in the water passages. When using 59 style heads on an 8 BA, you must plug passages in the head and block.
  4. adam401
    Joined: Dec 27, 2007
    Posts: 2,410


    When putting early heads on a late block theres a couple water passages towards the front that need to be blocked. If doing the opposite I'd imagine youd have to do the reverse. Somehow seal the holes in the head? Just put the heads on on the engine and look. You could also drop them on with 2 bolts loosely holding the head and roll the engine over by hand to see if theres any interference.
    The eab head is a nice option on a later block but for 48 and earlier theres so many nice looking aftermarket heads that were made its almost a shame to not go that route after all the work of a fresh build.

  5. Model A Gomez
    Joined: Aug 26, 2006
    Posts: 1,423

    Model A Gomez

    I put the early heads on an 8BA and had to plug two water holes in the block and one in the head, I think there are several holes in the heads that don't line up when you put the later heads on an early block. I think either milled stock heads or after market heads would be the way to go.
  6. tubman
    Joined: May 16, 2007
    Posts: 5,497


    I am assuming we are talking about a '39 Ford here, not a Mercury. The Ford's have the smaller 3 1/16" bore, while the Mercury's have a 3 3/16" bore (the same as the "EAC" series Mercury's). Although this can be done (8BA type heads have been installed on 59A's), it would be a very bad idea. This is because he would be using heads with a combustion chamber designed for an engine with a 1/4" longer stroke and 1/8" larger bore and would probably give him a compression ratio of around 5:1 and most likely provide very bad "quench" characteristics. "EAC" heads have relatively large combustion chambers for the 8BA series of heads to keep the compression ration the same as the current Fords.

    There has always been a misconception around the fringes of the hobby that Mercury heads are better than Ford heads because the Mercury's for any given year had a higher rated horsepower rating. Exactly the opposite is true.
    Desoto291Hemi and rusty valley like this.

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