HELP PLEASE WITH IDing A FLATHEAD BLOCK

Ghost of elmirage

Ghost of elmirage

Senior Member
Hello everyone can some one tell how to ID my flathead block? I think its a 39 to 42 . The only markings I can find are are the number 56642 on the intake manifold gasket surface and a cast in letter X on the top of the bell housing and that is pretty much it. Also at the top of the bore on all the cylinders there is a small step that appears a sleeve would have seated at one time. When I took the motor apart the pistons had a .0825 stamped in the top. PLEASE HELP!! Any ideas ? OH yeah it was a factory rebulid at one time as it had the FOMOCO tag riveted to the side of the bell housing . THANKS Geoff
 
A. Bore below step...this should be roughly .080 more than original bore
B. Are there 2 freeze/casting plug holes in each pan rail?
C. Manifold surface...flat all the way across or gasket-shaped cast pad in center?
D. Center vertical row of water holes...shapes of bottom 2.
 
Hi Bruce thanks for the reply

A. Dont know
B.yes right below the water pumps like 3/8 pipes thread
C. Yes aboout 1/16 of a inch raised and shaped just like the intake manifold and gasket
D. No the middle and bottom one are very similar but the top one is much ike an upside down tri-angle
 
It is a 39-42 ,you don't say if it is a 3 1/16 or 3 3/16 bore .in either case it is a US engine that has had tin sleeve's ,they could be pulled and 82.5 pistons put in the hole that must have been done during the rebuild..How about the pencil test on the front of the engine that will tell you if it is a 39-42. Remember the engine is 80+ over bored Hopefully it will clean up for 100.after that it might get dici.for a street engine you may have to use cast sleeves to bring it back to standard.Johnny.
 
Lay a pencil on the ledge at the top of the timing gear housing. If it stays there it's a 39-42 (?). I always thought the pencil test only worked on a 40.
 
OK...sounds like it is '41 or '42, or a wartime version of those.
Rough bore measure...do it with a ruler aligned as well as possible with bore below step.
I think you will see 3 1/16 plus a bit, roughly 3 1/4. Next stop would be 3 3/16 plus a bit. Think small bore because of cooling holes. Gonna be '41-2 85hp.
 
On the drivers side front of intake manifold gasket surface the number 56642 are stamped clear as day . Do these mean anything at all?
 
Last edited:
Nope. Go cut a strip of cardboard to 3 1/16 long and another to 3 3/16. I bekieve the first will go in with a touch of slop and the second will not go in. '41-2 221, rebuildable to 239.
 
Ghost of elmirage said:
Hello everyone can some one tell how to ID my flathead block? I think its a 39 to 42 . The only markings I can find are are the number 56642 on the intake manifold gasket surface and a cast in letter X on the top of the bell housing and that is pretty much it. Also at the top of the bore on all the cylinders there is a small step that appears a sleeve would have seated at one time. When I took the motor apart the pistons had a .0825 stamped in the top. PLEASE HELP!! Any ideas ? OH yeah it was a factory rebulid at one time as it had the FOMOCO tag riveted to the side of the bell housing . THANKS Geoff
Click to expand...

IF POSSIBLE post lots of photos of the block.
 
Thanks Bruce I will do the cardboard strip thing when I get home from work tonight. And 19Fordy I will post a bunch pictures as soon as I can get one of my kids to stay home long enough to show me how to do it haha I am a computer dumbass
 
I really dont care what CU the motor turns out to be when its finished I just want a flathead in my car Ya know ? Nothin beats a flattie and 39 box
 
Great! A 221 can typically be bored out to 3 3/16 with some room left for future rebuild, and so can be built as a 239 or 255 with no sweat. If it hasn't been messed with, you can also press in a new set of the thin shell sleeves and rebuild it at original 221 bore with no need for a bore job...that was the idea of the thin sleeve "tin can" bores. If you choose, I think the 255 configuration is very nice and worth the higher cost of getting a Merc crank. Not much $$ in terms of the total build.
If it turns out to be an original 239, those have extremely thick walls and can be built to any size in the flathead book from 239 up to steamer...
What is it going into?
 
It going into a 28 roadster pickup, just pickep up a frame already have a complete 36 rearend with juice brakes and also a dropped model A front end and a very nice set of split wish bones that a buddy built for me. I also modified a set of 51 F1 spindles and brakes for the front end . I like designing and fabbing stuff to I bought a 32 K-member and made some drawings and am going to make my own from scratch. I sold the K-member so I throw that money back into the car. I have a set 34 pedals for that will go onto the K-mamber as well.
 
The threaded holes below the water pump sound like the drain holes, not the core clean out holes for a 39, 40, early 41 engine. No core plugs 41 or higher. No bumps on the side not a 41.
 
I am a genius!! LOL NOT REALLY I just remembered that I still have one of the old pistons that came outta the motor when I tore it down rolling around on the floor of my truck. Now I know that pistons are not perfectly round , but I measured it roughly at 3.122 or so. So given that the piston is marked .0825 that must mean that originally the block was an 221 CI 85hp. Bruce, Johnny,Lawson,19Fordy,Joe KCMO? Am I on the right track?
 
Yup...engine was rebuilt by just yanking the sleeves and inserting the special oversize pistons made for this exact purpose. A little more and you can use standard 239 or 255 pistons.
 
will I be able to get to 255 CI with the 3 and 3/4 crank? I dont want a street killer . I am only going to dress it up with aluminum heads and dual carbs . I just want to cruise the the beach and eat fis n chips
 
You must log in or register to reply here.
Back
Top