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Technical 81 A flathead

Discussion in 'Traditional Hot Rods' started by terry k, Dec 7, 2018.

  1. terry k
    Joined: Jan 8, 2007
    Posts: 3,455

    terry k
    ALLIANCE MEMBER
    from toledo oh

    I have been cleaning the shop and moving things around. Had an engine in the back for 15 yrs. I thought it was a 59ab, but on cleaning the dust off I see it is a 81 A. Took this out of my '34 5W. Not to familiar with this one. What year would it be and what is the difference between it and the 59ab. Thanks Terry
     
  2. alchemy
    Joined: Sep 27, 2002
    Posts: 12,609

    alchemy
    ALLIANCE MEMBER

    The 8 in the 81A means 1938. It was designed in 1938 and is probably from that production year. Some parts carried that number into the next year's, but 39 got upgrades so it might not have been made in 39.

    Lots of little things are different, but the main thing different from a 59A is the bore size and the valve angle.
     
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  3. terry k
    Joined: Jan 8, 2007
    Posts: 3,455

    terry k
    ALLIANCE MEMBER
    from toledo oh

    Thanks for the info. Is it worth building or sell to a restorer ?
     
  4. Also ask on Fordbarn.
     
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  5. alchemy
    Joined: Sep 27, 2002
    Posts: 12,609

    alchemy
    ALLIANCE MEMBER

    Every flathead is worth building. Just depends on if you want a cruiser or a racer.
     
  6. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,494

    Bruce Lancaster
    ALLIANCE MEMBER

    You need a lot more info! The 81a designation is for the cylinder head. Versions of that head were used on 221's for several years, I think through 1941, and they will fit on numerous OTHER flatheads either without change or with very simple mods...really, ALL the flatheads later than 1938. Multiple photos of block and removal of a head are really necessary to figgeritout. It can potentially be identified within a year or two with enough clues.
     
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  7. alchemy
    Joined: Sep 27, 2002
    Posts: 12,609

    alchemy
    ALLIANCE MEMBER

    I guess I assumed the parts were all living on their original block.
     
  8. flatjack
    Joined: Feb 13, 2007
    Posts: 842

    flatjack
    Member

    81A was cast into some of the bellhousings. 38 was a strange year as they went from 21 stud to 24 stud. Also some of the blocks retained the 36 crankshaft with 2.339 main bearings but had 24 studs. All were 3 1/16" bore.
     
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  9. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,494

    Bruce Lancaster
    ALLIANCE MEMBER

    Almost all '38 24 studs apparently got the small crank 24 stud block, changeover to big crank block was apparently done late in '38 year so block of that type still got 81 A designation. The parts book labeled crank and block 81A-A
    (second A at end of part number) while the 221 parts used thereafter for several years had -B at end of the changed part number. I think! Very confusing.
    By visuals...the earliest 24 stud 221 has crank that ends flush with the front of the front cover like all previous flatheads. Later type (and all the later flatheads) had about 1" of crank protruding out of front cover and also the extra crank length sticking past the general plane of the pulley.
    This lengthening was done to support the crank mounted fan introduced with '39 standard cars. This longer crank also had the bigger mains, same diameter used on flatheads until 1953.
    Simple, yes??
    The '38 24stud engines are as scarce as they are confusing.
    Any prewar 24 stud engines need a lot of decoding to fully identify!
     
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  10. flatjack
    Joined: Feb 13, 2007
    Posts: 842

    flatjack
    Member

    I've got one of those 38 81-A blocks and was going to fit a later crank. Found out that would not work. Very confusing since both blocks have the 81A cast in the bell.
     
  11. terry k
    Joined: Jan 8, 2007
    Posts: 3,455

    terry k
    ALLIANCE MEMBER
    from toledo oh

    I pulled the intake off of the engine when I pulled it just to look in the valley. Been sitting all these years. Can turn over by hand with the heads on. Guess I'll place it up for sale as I still have a 59ab left over.
     
  12. Petejoe
    Joined: Nov 27, 2002
    Posts: 9,560

    Petejoe
    ALLIANCE MEMBER
    from Zoar, Ohio

    You fire up that racing engine yet Terry?
     
  13. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,494

    Bruce Lancaster
    ALLIANCE MEMBER

    Ron Holleran posted the recipe for putting later cranks in '36-38's. There was nothing exotic to the procedure really, but it required a sharp machinist with good measuring skills! It simply took removing metal from the crank mains and I think cutting one of the mains to a bit longer I think. I didn't pay much attention as i had no such block...
     

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