Register now to get rid of these ads!

How can I tell a Merc flathead from a Ford?

Discussion in 'The Hokey Ass Message Board' started by rainh8r, Feb 25, 2011.

  1. rainh8r
    Joined: Dec 30, 2005
    Posts: 792


    I'm going to look at a 52 Merc for parts, and it has a flathead in it that is supposed to be the original Merc engine. Except for the heads, is there any way to tell a Merc from a Ford externally? Thanks, Rob
  2. flatford39
    Joined: Dec 3, 2006
    Posts: 2,800


    Not that I am aware. If the heads are off measure the stroke. A Merc will be 4", a Ford 3.75" but you need to spin the engine to TDC. If it's locked up it's a crap shoot. I think 52 Merc's were painted seafoam green, but that's about the worst way to identify an engine.
  3. Ralph Moore
    Joined: May 1, 2007
    Posts: 651

    Ralph Moore

    Pull the pan and check the crank, it's the only way to know for sure. Merc crank will have a larger plug than Ford, 5/8ths I believe as opposed to 3/8th's, I know I can stick my little finger in the Merc plug, not in the Ford.
  4. oj
    Joined: Jul 27, 2008
    Posts: 6,281


    What about the script on the heads?

  5. rainh8r
    Joined: Dec 30, 2005
    Posts: 792


    Thanks, that was what I was afraid of. It's easy to put the Merc heads back on the replacement Ford block, but it's not the same underneath. If it turns over, it will be worth the price (cheap). It's a 4 door with rusty floors and fenders, but I hate to see them go to the crusher if there's something useful on it.
  6. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    Member Emeritus

  7. dabirdguy
    Joined: Jun 23, 2005
    Posts: 2,404

    Member Emeritus

    Look at the hubcaps.
    If there is a guy on them with wings on his hat... THAT's a Mercury.
  8. rotenjon
    Joined: Oct 26, 2009
    Posts: 111


    like mentioned above only way to know for sure is measure the stroke or check the crank. my engine is a candian ford block with canadian mercury heads, when i opened it up it was definatly a ford with a 3.75 inch stroke.:(
  9. Was wondering some of the same things while I'm learning about flatties. Thanks for the post, and thanks for the answers guys.
  10. Merlin
    Joined: Apr 9, 2005
    Posts: 2,546

    from Inman, SC

    My thought also. What you talking about willis?:)
  11. Dale Fairfax
    Joined: Jan 10, 2006
    Posts: 2,585

    Dale Fairfax
    Member Emeritus

    Personally, I'd rather pull a head than get under the car and try to wrestle the oil pan off just for a look see. Plus, the check you can make that way is more definitive than looking at the crank.With a head off, all you have to do is stick a ruler down in the hole--any measurement over 3 3/4" confirms the 4" stroke.

  12. spooler41
    Joined: Feb 25, 2007
    Posts: 1,099


    Rainh8r, any flat head that will role over is worth saving, be it a Merc or a Ford.
    Good luck with your quest.

  13. blown49
    Joined: Jul 25, 2004
    Posts: 2,212

    Member Emeritus

    Crank clean out plugs.

  14. I have heard from a reliable source that the deck is slightly higher where the intake mounts on the Merc blocks.
  15. saltracer
    Joined: Jan 4, 2006
    Posts: 293


    That's a new one on me.
  16. You're mixing facts here. What your 'reliable source' is most likely talking about are early 39-42 Merc blocks (24 studs - cast-in bell housing). The early 239's (which were Mercs) had a raised area on the intake surface, which was one of the ways you could tell a Merc block from a Ford.

    These early 'keystone water passage' blocks are great blocks for a performance flathead build - but they came with a 3.75 stroke crankshaft, full-floater rods, etc.. 3 3/16 bore x 3.75 stroke - 239 cubes.

    And yes, you could drop a 4" 49-53 stroke Merc crank into them - just like any other 24 stud flathead.


    In 49-53, I've never seen any differences in the blocks between Ford and Merc.

    If it was me, I'd pull a head. Given that normally a late engine has head bolts instead of studs, it is butt simple to pull a head and measure the stroke (as long as the engine is "free"). If it is stuck, this won't work.

    As some noted, the crankshaft and stroker pistons are the only major difference. The most common way to checkout a crank is the 5/8" rod-throw clean-out plugs . . . though, there are some 4" stroke cranks that had the smaller plugs (especially in Canada). The most reliable way is to measure the WIDTH of the first big counterweight on the crankshaft (closest to the front). If the width is over 6", then it is a Merc crank - under 6", then it is a Ford.

    Best of luck!

  17. That's what I get for opening my big mouth! Haha! Oh well, at least I have partial memory retention. And I'm sure my omission of all the info was mine and not my 'reliable source.' I am still learning (at 38 years old.)
    Last edited: Feb 26, 2011

Share This Page

Register now to get rid of these ads!


Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.