Building a 255 from a 221 block, help needed.

3

39fordtruck

Junior Member
Hi I’m helping a friend build a flat head. He does not do the interweb only has a flip phone and doesn’t do texts.
We are starting with a 1940 block 221, 24 stud engine. It has been bored to standard 239 with no problems.
Plan to use 4” mercury crank from an 8BA. Flywheel from a 59ab.
The crank is turned 10 under.
We have Std mercury pistons. And 8BA rods.
Plan to use a crab distributor.
Question: I think we need 8BA rear crank main bearing and 59ab middle and front bearing, 10under? Do we have to buy 2 sets or does someone sell individual ones? Maybe someone will have the early or late ones they would part with. (10under)
Will I have to use the timing gear from 59ab crank, correct?
Can I use the mercury 8BA cam or do I have to use the 59ab cam?
Will 8BA valves and adjustable lifters work in 40 block?
I have a mismatched set of 81a and 91a alum heads I hope to use they cc to something close to each other.
That’s about it I probably missed a bunch of stuff. Building on a budget trying to make what We have work.
 
Just a hint. Using Mercury and "8BA" referring to the same items can be misleading. The Mercury's were actually "8CM", "1CM", or "EAC". The "8CM" Mercury cam is actually a good upgrade over the 8BA.

Just picking nits here, but information is power.
 
some 221 blocks will have connecting rod interference with sides of block, a little grinding may be required. I have a 59ab with a Merc crank, it is apart for another problem, I will check on a few other items if need be. seems to me that the old V8 parts store had some kind of rear seal adapter made up. maybe someone with more knowledge will chime in
 
You need the rear main bearing for the 39-48 block. The 8 ba rear bearing won’t work. Also need the upper and lower rope seal holders. One of them has a 19B prefix can’t remember right off which one.
 
The front and center mains are the same on the 59AB and 8BA so a 59 AB set will work. Fine to use 8BA valve gear. With the crab distubutor, you will need a 59 style cam and change the crank gear to the 59 type and use a 59 cam gear.
 
With the crab distributor can I change the gear on the later mercury cam with one from the 59ab cam? Or do I need to use a 59ab cam as is.
Will have to check about the clearance on the bottom of the skirts.
I thought there was a mix and match with the main bearings when using a later crank in early block?
Thank you for the quick replies. This info really helps a lot.
 
One of the Tex Smith books had a run down on building a 255 21-stud engine using the 8CM crankshaft. Main bearings always follow the block in flatheads as a general rule. Cranks can be cut down to fit on any of the old blocks but a lot depends on the size of the mains for the block and how much clearance the crank will have in the block. The counterweights may even require some turning to clear the early blocks but I don't know about the 24-stud 221 blocks. A person just has to try it and find out. Anything can be done but sometimes it gets more expensive to get there. The work that was done on the block for the Tex Smith book article was extensive but it worked well afterward. It ran in a 1935 Ford coupe for the Great American Race and it definitely finished.

The 59 series cam gears are cut to thrust toward the block where the 8BA family cam gears thrust toward the front to keep good engagement with the distributor drive. Valves are pretty much interchangeable between early and late if the corresponding valve guides are used. All of the early style frontal components from the 59 series back will have a better fit in an early car or pickup.
 
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FlatJack9 has it right. The reason you want to change the crank/cam gears to the earlier 59 series ones is that the thrust is opposite from the 49-53 gears. On the earlier gears, the thrust is towards the block, on the 49-53 - the thrust is toward the timing cover.

Also, run the 49-53 oil pump and the special oil-pump pickup tube that Speedway has (to fit your earlier 59 series rear-sump pan).

For connecting rods, run the 49-53 rods with the insert bearings - a lot easier to setup than the full-floater bearings from the 59 series engine (especially if you've never done it before).

Have everything balanced . . .
 
Make sure you mockup the block with one piston and rod (on each bank/side) and clay the tops of the pistons to check your piston to head clearance (with a head gasket in place). Depending on the dome type of the piston and your heads, you may or may not have a consistent clearance to the head. I like to achieve about .040 clearance. In many cases the heads need to be surfaced to achieve this. It makes a huge difference in how a flathead runs.
 
I might be wrong,,,,but I think I remember Bruce Lancaster saying the main bearings are crankshaft sensitive .
The block doesn’t matter bearing wise .
The front and middle mains are the same,,,,the rear is different .

Use 8BA mains with an 8BA crank ,,,,,or more precisely,,,,,8CM crank ,,,LoL .

Yes,,,,the timing gears are different,,,like the man said .

Tommy
 
Desoto291Hemi said:
I might be wrong,,,,but I think I remember Bruce Lancaster saying the main bearings are crankshaft sensitive .
The block doesn’t matter bearing wise .
The front and middle mains are the same,,,,the rear is different .

Use 8BA mains with an 8BA crank ,,,,,or more precisely,,,,,8CM crank ,,,LoL .

Yes,,,,the timing gears are different,,,like the man said .

Tommy
Click to expand...

The main bearings are block sensitive, not crank sensitive. The block does matter bearing wise. the crank does not matter bearing wise.
The front and middle are the same, the rear is different, but it is the block that is the deciding factor.
 
I think you will need the specific oil seal (rope type) inserts for the rear main cap and rear of block. Your block is probably set up for a slinger type crank.
 
Great info, Ive been toying with the idea of a merc crank in a '40 block here myself. And every question ive had so far has been covered .
 
Its not a big deal to cut the gear off the merc cam and slot it for a crab dizzy. Even a dope like me can do it !
 
Why would you want to run an early distributor, when you can run the best one for the application. Modified SBC unit.
Gramps
 
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