Crankshaft length

Joe KCMO

Joe KCMO

Senior Member
How long should the crankshaft stick out of the front cover for 38 to 41 Ford 24 stud v8's. Was the mercury 39 and 40 motor have the same length. Trying to determine crankshaft in my motor.
 
I can't tell you without a trip home...but do you have a pulley??
'38 type, the short 24 stud one/same length as earlier cranks, uses the early short pulley, and crank ends right about the plane of the single sheave. All other 24's from 1939--1953 come out substantially farther. If single sheave pulley, the pulley has an extended center tube extending well past the plane of the pulley to meet crank length. If '39 deluxe--41 fan type pulley or '42-8 double pulley, crank extends to meet the ledge where crank ratchet screws down the washer.
 
So...early protrusion is precisely real damn short, plus or minus .005. All other crank dimensions if you drop pan will differ from late.
One oddity I turned up...bought a '42 type pulley that was plugged with something. Drove it out, discovered I owned what appeared to be a well made extension of the right length to adapt early crank to '39-up pulley. Some kind of rebuilder's special... they would adapt anything to anything to get another engine sold.
 
No. The short is the 68 prefix one used on replaceable main 1936 and on all '37-8, 2.398 original mains, late is 91A with 2.498 mains, short snout.
 
Has anyone ever cut a long crank to shorten it up? I want to put a 53 crank in a 39 block and make it look like a 38 24 stud motor.
 
If your '39 is the normal and common long crank one, it is the same length and takes same types of pulley as will go on a '53.
If it is the short crank with the 68 crank, it needs a lot of rework to fit it in there as mains need complete re-do.
 
The late crank as made (any original 239 or 255 crank from '39--53) is made for the larger diameter rods. You can use the good floaters on any of them, late locked rods only good on '49-up.
I've never used this combo, but if you put in a 239-255 crank (drop-in on long crank '39, requires substantial cutting on a short crank engine) Ol' Ron says you need to assemble rods from the bottom unless you bore to 3 3/16...
Alternatively, the big throws can be cut or offset cut to take the 221 rods and bearings.
 
I have a 38 standard coupe that I want to look stock. I have a 39 mercury motor, 38 24 stud heads (I would love to find a nos pair), and a 53 merc crankshaft. I plan on building a 255 inch motor that looks like a bone stock 85 horse motor, thus the question about shortening the crank.
 
For appearance, and to keep the pulley with no extension on the front, I don't see why you could not just cut off the requisite amount and drill for the retainer ratchet. The diameter where pulley goes is the same. The '39 Merc you have would be ideal in terms of external details, too.
I do not have the length spec or a 68 crank to measure.
The Merc is ultra-thick and would make a VERY safe 4:00 X 3 5/16. If you can find the ultra rare 81AS Denver head you can really yank up the compression with 1938 vintage heads, too...
 
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