Light cranks

[3W Hank]

I guess crankshaft weight might not be a priority thoughts.
Common since 49 is the 4”, free cubics from the 3.75, but strokers was fast there at 1/8 or 1/4 by weld.
Weight is seldom maybe concider but I has seen very nice crank from way back then but newer weight them but I heard of cranks with thinner counterweights, but what year was that, a indication is under 1939 but not shore, and I’m into big main/rod figuration.
How much central force help can be discussed, but not focus on that just who was the lightes cranks ( 59A style )

 

[38 coupe]

Crankshafts for the 221 - 239 - 255 family of flathead V8 engines came in a variety of combinations. Two different snout lengths were used, two different rod journal diameters were used, and three different main bearing diameters were used. Off the top of my head I think the following are the major crankshaft types produced in the USA, but I might be missing a detail or two. Van Pelt has a nice table with this information by year. In general the smaller bearing crankshafts will be lighter than the larger bearing crankshafts.

1. 1932 crankshaft - forged, short, 1.999" diameter mains and rods, one oil hole in the middle of each rod journal, 3 3/4 stroke
2. 1933 through 1936 Babbitt main crankshaft - cast, short, 1.999" diameter mains and rods, one oil hole in the middle of each rod journal, 3 3/4 stroke
3. 1936 (with insert mains) through 1938 crankshaft - cast, short, 2.399" mains and 1.999" diameter rods, one oil hole in the middle of each rod journal, 3 3/4 stroke
4. 1939 through 1942 221 (85 hp) crankshaft - cast, long, 2.499" mains and 1.999" diameter rods, one oil hole in the middle of each rod journal, 3 3/4 stroke; can have either labyrinth type rear seal or rope type rear seal
5. 1939 through 1948 239 (95 - 100 hp) crankshaft - cast, long, 2.499" mains and 2.139" rods, one oil hole in the middle of each rod journal, 3 3/4 stroke; can have either labyrinth type rear seal or rope type rear seal
6. 1949 through 1953 239 crankshaft - cast, long, 2.499" mains and 2.139" rods, two oil holes per rod journal
7. 1949 through 1953 255 crankshaft - cast, long, 2.499" mains and 2.139" rods, two oil holes per rod journal, 4" stroke

Notes on Crankshafts from the engine identification thread:

• 1.999” main Babbitt crankshafts can be installed in engine up through the 59 series. Ford made special thick insert main bearings to allow this. If you have a good Ford parts catalog, some patience, and search you can still find these. Frequently there are some on that auction site. Any flathead insert main bearing with an “18” prefix is one of these special swap bearings.
• 2.399” insert main crankshafts can be installed in engine up through the 59 series. Ford made special thick insert main bearings to allow this. If you have a good Ford parts catalog, some patience, and search you can still find these. Frequently there are some on that auction site. Flathead insert main bearing with an “68” prefix and suffixes G, H, J, K, L, N, P, X, and Y are special swap bearings.
• 2.499” insert main crankshafts can be installed in any block made for 2.500” bearings. You must use the rear main bearings that match the block type. If the crankshaft was originally made for floating rod bearings and has only one oil hole per rod throw you must use floating rod bearings and matching rods. If you want you can use floating rod bearings and matching rods on 8BA era cranks, but the only reason to do that today is if you are running a 1/8th stroked crankshaft and need the prewar Ford rod bearing size.

 

[3W Hank]

Good info, thanks !

At the #5.
From what I heard ( say a 'rumor' ) all or some of those cranks under 1939 had a thinner counterweight.
But from this ( under #5 ) all cranks with big main/rod is the same up to 48, or was the crank just under 39 ( big main/rod ) that had thinner counterweights than ex at 1940 ?

-Guess a hard question if someone really has set them self into this !
But I found it intresting.

Its not really gain HP, its more a cool thing to know or to use.
A heavy crank don't get less HP, but rew is faster, so common race things is a lighter rotating, or less friction and less weight of crank.
Ex in my new 426 Hemi I order this Crower crank with gunholes in mid and that was 3.5 LBS lighter than my other Crower. So race guys like get around.

In this coupe its pre 49 and trix that was used, or could been used.
I rather go less stroke than has over 4" as a light car and I like the rew.
I could go std 3.75 aswell as has a short nose small main/rod crank very nice pice.
But the bearing issue will get me in a problem.

So a baby stroker 59A crank might fill my idea !
Just like to search for information if the 39 crank really had thinner counterweights.

 

[Brian]

I seem to recall reading an article in a hotrod magazine years ago, about Barney Navarro whittling quite a substantial amount off of a flathead crankshaft counterweights in order to lighten the thing.
Would definitely be easier to do what I do; machine the lip off of an early flywheel and use a 9" Auburn pressure plate.

 

[3W Hank]

Yes that parts I made in found a aluminium flywheel and I bought a Aburn pressuare plate via Hamb, but at 10".
If central parts on the crank its reduced in total weight and one can still balance.
If a crank/design ( ex thinner weights ) its free lower weights.
I guess its hard know the weight.
I looked at a NOS 1939 crank today but I was not able see any partnumber or measure the counter weights.

I wonder if someone could weight a ex 37 crank ( short nose, small main/rods ) and a 59A crank ( 39-48 ) and a 4" Merc crank.

 

[Ronnieroadster]

Get the crankshaft as light as possible even if its a 3-3/4 stroke. Is it easy no is it worth the effort heck yea. Knife edge as well and complete it be polishing all the surfaces to shed the oil as fast as possible.
For crankshaft weight I can tell you my Merc crankshafts weight less than a 59 A crank which is about 10 pounds lighter than a Ford 8BA crank which is also lighter than a Merc crankshaft.

Here's a Scat crankshaft that I detailed by making all the surfaces nice and smooth compared to the as cast rough surfaces. The crank is now a bit lighter and an added bonus it will shed oil off the surfaces better than that rough original as cast surface.
Ronnieroadster

 

[38 coupe]

The stroked cranks I have seen have substantial balancing holes drilled in the counterweights to balance the lighter rod throws, that also helps make the crank lighter. If you really want light crank instead of more cubic inches you could machine a crank like the old 1950s SCTA Class B (under 250) contenders who de-stroked a 3 3/4 crank by 1/8". I would go for the cubic inches, it will make drivability with your cam better.

 

[3W Hank]

Yepp, that is fun readings.
Allot of work.
Minus over 10 LBS and still in balance,.

Questions ;

1, Did you cut the OD something ?
2, Did you get to the 50% factor ?


I’ll seen some weight listed on internet but they say pre 39 45 LBS and 59A 46 LBS, so the older short nose was tad lighter.
But the trix is grinding to reduce weight.
Smaller OD cut oil better so one way is turn the diameter down but that is the wrong way for balance, so material remove is central.
If anyone has a picture of old race cranks I sould love to see them !

 

[glennpm]

Good article here:


https://www.motortrend.com/how-to/ctrp-0410-crankshaft-developments-race-engine/