Chevy Crankshaft Casting Numbers

Chevrolet crankshafts fall into one of a number of catagories,big,small block,large and small journal,cast or forged,internally or externally balanced,round or two piece rear main seal.

The casting numbers on the Chevy cranks can be confusing to say the least.Forged crankshafts have less prominent numbers than cast-iron,that comes from the fact that the numbers are not cast into forged cranks.It can be very confusing as to how many numbers are actually on the crankshaft itself,quite often,only the last four digits show up!The number 3941178 Crank might be described by collectors as "1178"

Casting numbers on the crankshaft itself will obvoiuslyI.D. it's application but,other features should be checked out at the same time.Be sure to look at the parting line on the crank.Cast cranks have a narrow parting line where the two pieces came together in the mold.Forged cranks have a much wider parting line giving the appearence that the line was ground off.Forged cranks are stronger by far than cast and were used in most of the high performance applications.

Something else to make a note of is weather or not the crank is internally or externally balanced.Externally balanced cranks are used in engines that do not have enough counter balance weight inside the block.The 400 small block and the 454 big block Chevy engines are the only ones from the factory that require external balancing.Requiring the use of balanced flywheels as well as harmonic balancers.

Early 1968 marked the enlargement of the small block crank journals,hence,small journal cranks are pre 68 and large journal cranks are post 68.

Crankshaft Date Castings.

Date codes I.D. the month ,year, and the day that the product was manufactured.A letter would indicate the month while numbers indicate the day & year.The year code can sometimes cause some problems because you will not always be able to I.D. the correct decade.Meaning an 8 could be 68 or 78.Casting numbers are not always visible on the cranks.

Example:C238
C=March
23=23 rd day
8=1968 or 1978

Month Codes
A=January
B=February
C=March
D=April
E=May
F=June
G=July
H=August
I=September
J=October
K=November
L=December

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