Oldsmobile 425ci Crankshaft und Flexplate

Early cranks [330, E-400, 425] require an early pattern

Early series big block, short stroke, all forged. 400, 425's have 'em. They have an "L" or "check mark" shaped notch on the drive flange.


Quick, low-hassle ID tip: On the back of the crank, on the OD of the flange to which the flexplate or flywheel attaches, is a notch. Forged cranks [330, early 400, 425] have an L-shaped notch. Cast cranks [350, almost all 455's, late 400 engines] have a notch shaped like a tall C (or a wide U).

Early big block forged steel crankshafts carried ID #390370 or 384722. This unit, used in the 442's early 400 engines and all 425's, has a stroke of 3.975". This crank can make an early 400 engine [using a 4.000" bore E block], or a 425 [with a 4.125" bore A, D, or F block and 425 pistons and rods], or a 455 small block [with a 350 Diesel block and about $3000 worth of Mondello parts]. A 455 big block cannot be made from this crank.

Specifics:
400943 crank, numbers barely visible, on the rear weight. Notch in rear face is a 'rounded-L' shape, longer than say a 425's L, and the corner is smooth, not a nice right angle. Just like Mondello's tech manual shows, except he shows a sharp corner there. Forging flash removal left a very wide "part line" as per usual for a forging. The front throw has AC stamped in it.


http://www.classicoldsmobile.com/tech/