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Technical Flathead Guru's! - 21 Stud Flatty Good For Stroking?

Discussion in 'Traditional Hot Rods' started by 28A, Mar 5, 2014.

  1. Hey fellas,

    Have been having a few conversations with an old timey local rodder and he's been telling me the 21 stud Flatheads are good candidates for stroking due to something to do with the early crank and rods. Is there any truth to this? Is it a relatively easy or a hard job to have done? Time consuming / costly?

    Would love to hear all about this one from the guys on here that know all about it.

    Thanks.
     
  2. khead47
    Joined: Mar 29, 2010
    Posts: 1,566

    khead47
    Member

    Old guy was probably thinking the RODS are good for stroking. Smaller big ends. Use the rods for offset ground crank.
     
  3. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    Uh...they made several models of flathead.
    '32-6 with small crank and poured mains require radical work on a late crank, far more than just turning it down.
    '35-6 and '37-8 21 studs can take later cranks with only fairly simple turning down of mains, potentially allowing 4, 4 1/8, and aftermarket strokes.
    Small bore means pistons get assembled to rods in engine, not a big deal, and some models of 221 can be bored out to the 239 type bore.
    Early 221 type rods are used to allow stroking of the bigger 239-255 rod journals to give a 1/8 increase in stroke on those.
     
  4. The engine i have is a '37 21 stud. The center water outlet, pumps in block type. Its a virgin bore currently. Is this something that could have the crank offset ground to allow for stroking?
     
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  5. Heo2
    Joined: Aug 9, 2011
    Posts: 661

    Heo2
    Member

    no you need the later crank
     
  6. I have a crank that came out of a '40ish block, i've looked up last night about identifying it but not really sure if its a merc or a ford one.. So is it the early rods that people use then for stroking?
     
  7. hotrodderhaag
    Joined: Jan 22, 2007
    Posts: 2,109

    hotrodderhaag
    Member

    this gives me many ideas for when i tear down my 37 flatty in my model a. i want to make it have a little more ass with a lopey cam, these will go well with the McCulloch supercharger
     
  8. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    Most '37 type blocks can go to 3 3/16 for 239 inches, and the '39-53 cranks can be ground down to fit. That offers original 221 size journal, big journals at 3 3/4 or 4, big journals offset ground to small journal for 4 1/8, and all of the aftermarket cranks.
    Later mains have to be reduced in diameter and otherwise lightly messed with, but nothing requiring tech beyond a good rebuild shop.
     
  9. DICK SPADARO
    Joined: Jun 6, 2005
    Posts: 1,887

    DICK SPADARO
    Member Emeritus

    For the time , effort and monies expended this is a no gain experiment in slightly improving your lawnmower engine performance. While it might sound neat to have all this stuff its still a low RPM engine and that is it. Unless this is used as a full out race engine where there was a specific class for it to run against similar combination this is nothing more than a bragging contest on who can spend the most money for the least gain. At the car show the average person doesnt know if your engine with the rough idle has all the goodies or just a bad spark plug rump rump.
     
  10. Well if thats the case that it isn't really worth doing.. i'll just go with a fairly standard rebuild, a cam change and a few bolt ons (twin carb manifold, exhaust headers.. the usual stuff).

    Thanks for the information guys!
     
  11. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    It's still a low RPM chug, yes, but boring to 3 3/16 (some risk, but reasonable) and putting in a stock Merc crank moves you from 221 to 255...that is a bunch of very feelable torque, and will give better return on any further souping.
    1937 torque peak, 155 or so, 85 hp.
    '50's Merc 255 goes over 200 and around 120...use the late innards and with VERY conservative cam and compression bump and you are there.
     
  12. lowsquire
    Joined: Feb 21, 2002
    Posts: 2,564

    lowsquire
    Member
    from Austin, TX

    Perhaps in America it may be vaguely feasible to build a stroker using small journal rods- but from all my research you're actually ahead financially using a scat crank and French rods to get the stroke increase. The machining costs here make it unworkable. I've paid up to 800 to have rods resized and straightened , plus the offset grind costs, and the inflated cost of floater bearings.. Just doesn't make sense to build a large flat motor the old way anymore in Australia. As dick says.. No one knows or cares what's in there.. Just how it sounds and goes.


    Posted using the Full Custom H.A.M.B. App!
     
  13. Thats a good point Ben, i haven't considered the cost difference here in Aus. I have considered simply boring the engine out to a 239 to give it a little more oomph per say. If i could find a merc engine or the internals, i would love to use those in my 21 stud engine to keep it somewhat unique. I rarely see flatheads up this way, and they are never a '37 - '38 21 stud.
     
  14. x 1000 ^^^
     
  15. Mart
    Joined: Mar 3, 2001
    Posts: 3,702

    Mart
    Member

    Can I ask a question?

    It is stated above that the 21 stud motors can simply be bored to 3-3/16" for 239 cu in. Are you sure? The positioning of the studs in the 21stud, ie directly below the bore, put them very close to the bore, plus does anyone make a gasket that will fit the 21stud and be ok with the big bore?

    Are we getting mixed up with the relatively much simpler operation of banging a 221 cu in 24 stud motor (many service 59A's) out to 239??

    I don't know the answer but had sort of assumed a 21stud motor was more or less limited to a stock rebuild overbore of +.060 or +.080 max. This is my assumption, if it is wrong I want someone to tell me.

    Mart.
     
  16. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    Wow! Lots of money there. Reworked Merc stuff would be a cost savings for someone well connected with a machine shop but that's out of control.
    However...remember the after market stuff is made to drop into '39-53 blocks, so to build an enlarged 221 you would still need considerable crankshaft machining, perhaps or perhaps not possible from the manufacturer.
    And another joker is that you would not want to risk bore bigger than 3 3/16 in a '37 type block, so again you are back at either stock merc parts or lots of special order on a kit. The torque difference with 255 or so would be very worthwhile either stock or souped, and would make a souped engine less of a compromise in low RPM range, but $$$!
    As a 255, if you did it with all stock Merc parts no rod throw machining would be needed but main work would be.
     
  17. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    The '37-8 221's have the reputation of being boreable that much. The early small crank 221's are very poor risks for larger bore, the '36 insert main engines seem to be like '37.
    I'm pretty sure the move to 24 stud was motivated by the upcoming move to bigger bore...I don't think there was any other need to be met there. Ol Ron on the barn has built enlarged '37 types. I think the risk level is roughly the same as the risks of building 301 and 352 engines from 283's...there are risks, but at a level tolerable for the hot rodder consciousness!

    (and...as with building a 352 283...this is basically an insane endeavor done specifically for the sake of tradition, difference from common approaches, and bragging points. A more sane person would start with a 59 A Ford or a 350 Chevy, missing out on all the entertaining problems, and a really sane person would just go buy a Toyota. I think that guy already left the HAMB...)
     
    Last edited: Mar 7, 2014
  18. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,341

    porknbeaner
    Member

    Bruce (and everyone else for that matter) with the posted cost for machine work down under it would almost be cost effective to ship the parts here have the work done and ship them back.

    As for building a 21 stud, sometimes it is more of I have done this traditionally as it would have been done back in such and such an era and less end result. If end result is what everyone is after there is no reason to run a flat head at all is there.

    Just being the devil's advocate here for those who are not yet acquainted.
     
  19. HOTRODDICKIE
    Joined: Aug 5, 2003
    Posts: 138

    HOTRODDICKIE
    Member

    A 21 stud in good fettle with dual carbs, headers decent ignition possibly a mild cam and a port job
    is a great engine to have and will provide more than reasonable reliable performance in a light car especially with a 5 speed box behind it, all that machining, stroking, risky boring, unless you are racing will be big bucks for little gain. Then the first time it needs another bore or grind it will be expensive scrap.
    Rich
     
  20. JeffreyJames
    Joined: Jun 13, 2007
    Posts: 16,597

    JeffreyJames
    Member
    from SUGAR CITY

    I have a '37 221 I am planning on putting a 4" crank into. Chris Swenson's dad has done a few and I think they are a bunch of work but I kinda want to explore the idea since I like the idea of running a 21 stud for some reason. Might be wasted money but isn't any money thrown at a flathead wasted money? I mean we do it because we love them and not because they're powerful, economical or what not.

    All great info on this thread. Let's explore more!
     
  21. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    If I were messing with one of these, I would put in the bottom studs that will be realdamnclose to the bore with a killer grade of loctite, being really careful to st vertically. as some extra support there. Heating will gettem out if necessary.
    Ron has I think posted some details of the crank cuts...mainly decrease mains, cut snout to match the '37, and I think there might have been a slight lengthening of one of the main journals. If you go to 221 rod size, you can start with a 4" crank that is worthless because it is damaged beyond big rod bearing availability.
    There are good pics of the various cranks with many of the dimensions noted in the prewar service bulletins to start you thinking. None of the mods really require anything more than normal crank grinding machine and an intelligent machinest.
     
  22. The process "Muffin" did to his 221

     
  23. nitro29
    Joined: May 26, 2005
    Posts: 66

    nitro29
    Member

    Hi, Just a thought but a bloke built one for a '35 coupe for one lap of America race. The build is in Tex Smith's book on Flatheads, just a thought. Roger
     
  24. Mart
    Joined: Mar 3, 2001
    Posts: 3,702

    Mart
    Member

    ^^^ Wow! Muffin and his Pop just turned the volume up to 11!

    Mart.
     
  25. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    Looking into totally bored out block is downright scary! I forgot about the build in Smith book...good reading.
     
  26. Mart
    Joined: Mar 3, 2001
    Posts: 3,702

    Mart
    Member

    Would the strength of that block be seriously compromised by the upper and lower deck surfaces no longer being held together by the cylinders as a single piece? Or does the interference fit give sufficient structural strength?

    I will tell you this, though, It's way beyond anything I would ever try.

    Mart.
     
  27. forty1fordpickup
    Joined: Aug 20, 2008
    Posts: 284

    forty1fordpickup
    ALLIANCE MEMBER

    I think the block would have enough strength in at the main bearing webs. I don't believe I could give control of that process to a machine shop without being able to watch over the operation. It's just a bit scary. It could be a solution to some cracked blocks. In any case it is a drastic mod.
    Chuck
     
  28. Imo just like any machining operation, if the time is taken to do it properly and the machinist is competent/conscientious, its not rocket science for them. I can see in the pix a ledge left at the bottom of the bore to accept the sleeve (very nice) and the judicious use of JB Weld as well. Nice work.

    Let's remember, 8 new sleeves will eliminate corroded original pieces and prevent cooling system hot spots and ring seal due to rigid/thicker bores.

    In addition, these engines are not slated for use in Top Fuel lol. ;)
     

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