Technical Notes

• Pre-1964 cranks must be machined to fit Turbo Hydromantic torque converters.
• Numbers on the crank are often the same as the part number, but not always.
• Replacement cranks may be a different part number or casting number than what came in the original engine.
• Bearings must be installed in the engine and measured prior to grinding the crank to get clearances right.
• Pilot bearing is # 7109 (GM part number 15533265)
• Size is 1.3780″OD x 0.5906″ID x  0.3543″W (35 mm OD x 15 mm ID x 9 mm W)
• Starting around 1966-1967, not all cranks used with automatic transmissions were machined for a pilot bearing.
• Bearing is slip fit into crank with shield to the outside.
• Crank opening is staked with a chisel in 2 places to hold bearing in place
• A common and cheaper 6202 bearing may be used, but the crank opening may need to be machined 2 mm deeper
• A 6202 is 35 mm OD x 15 mm ID x 11 mm W
• The 6202 is available with shields or seals on both sides to keep dirt out.

• ALL 326,350,389 AND 400’S HAVE A 3.00″ MAIN JOURNAL DIAMETER
• ALL 421, 428, AND 455’S HAVE A 3.25″MAIN JOURNAL DIAMETER
• ALL 265 AND 301’S HAVE A 2.50″ MAIN JOURNAL DIAMETER
• ALL LARGE JOURNAL CRANK SHAFTS HAVE A 2 3/4″ FLYWHEEL FLANGE.
• ALL PONTIAC CRANKS FROM 326 THRU 455 USED THE SAME FLYWHEEL BOLT SPACING AND ARE INTERCHANGEABLE.
• BE CAREFUL THOUGH AS 389/400 CRANKS COME IN 2 1/2″ AND 2 3/4″ SO BE CAREFUL WHEN SWAPPING CRANKS OR YOU MIGHT END UP CHANGING FLYWHEELS.
• FOR STICK APPLICATIONS, YOU CAN ENLARGE THE CENTER HOLE FROM 2 1/2″ TO THE LARGER 2 3/4′ WITH ANY PROBLEMS.
• BE CAREFUL WITH THE EARLY 389 “ARMASTEEL” CRANKS AS THE REAR CRANK REGISTER IS TOTALLY DIFFERENT AND THE LATER FLYWHEELS AND TORQUE CONVERTERS WON’T FIT IN THE HOLE. THEY CAN BE MACHINED TO FIT, BUT IT COULD BE AN EXPENSIVE OPTION.

   

Additional Information on Armasteel

The 1966-and  Armasteel cast crankshaft are not any stronger than the 1967-up cranks with “N” cast on them. Both are nodular iron. If you have the crank cross drilled, do not use fully grooved main bearings. It can’t hurt, but if the rods are prepped correctly and the assembly is completely internally balanced it is not necessary.
The last year that the Armasteel logo was used on a crank was in 1966. The factory determined that it was misleading because the cranks were not steel. The 1967-up cranks had “N” casting, meaning nodular, or the cranks had no logo at all. Nodular cast iron, also known as spheroid graphite iron, is that the graphite is present in ball-like form instead of flakes as in ordinary gray cast iron. This results in a casting of high strength and appreciable ductility. Its toughness is intermediate between that of cast iron and steel. It is more economical to make than steel because it can be cast in molds by the millions.
In the RA IV engines, the crank had “N” cast on it along with the RA IV crank part number. The only difference I could see between a standard 400 cu.in. engine crank and the RA IV crank is that the RA IV crank was machined with .001″ more clearance on the rod and main journals. Otherwise they were exactly the same.
Armasteel cast crankshaft were pearlitic malleable iron, with enhancements, they are not drop cast poured, but are centrifugal spin cast. Armasteel is less prone to cracking and pounding damage from detonation, not much, but a little more, and is denser in its basic structure. After the main casting process is done and the basic machining is completed, the fillet radiuses and main/rod journals are rolled in a hydraulic former, to make those areas stronger (about 10 to 15 percent stronger) than either drop cast or machined areas of the cranks. Buick also used Armasteel cast crankshaft, without problems, and all V6 Buick cranks, steel or iron, have rolled, not machine cut or ground fillet radii. Camshafts used to be made in two different materials, nodular and pearlitic malleable iron, non-harden able and harden able, for flat tappet cams, one for hydraulic and the other for solid lifter use.
And to further muddy the waters as to why some Pontiac engines in the mid-sixties got Armor-Steel cranks while others did not, note that “ALL” 65 326 engines (including the 326 2bbl, auto trans engines) got Armor-Steel cranks. Hummmmm.
The 326 Pontiac engines got the stronger “Armasteel” cranks because of the incredible amount of HP they were producing for their size.
The last year the Armasteel designation was used was in 1966. Therefore no 428 or 400 cranks were called Armasteel cranks. They were all “N” cranks.
I had a 1968 428 4 bolt and it has a Armasteel cast crankshaft. It says so on the crankshaft. I know this engine was never taken apart, and all original. There were a few selected engines other than the 421’s that they stuck the Armasteel cast crankshaft in, and the 428 was definitely one of those.
The 1963 421 #9770488 and the 1964-66 421 #9783787 crank is Armasteel. Then Pontiac started playing the “switch-m” game with the 1967-69 428 cranks and pistons. The 1964-66 421 #9783787 Armasteel cranks were used until the #9782769 “N” crank was introduced in 1967. The latter was balanced for the different type 1967-69 428 pistons. Apparently a few of the 1964-1966 421 Armasteel cranks and pistons were installed in the 1967-69 428 engines. The 1967-69 #9782769 “N” cranks are difficult to rebalance for replacement TRW 428 pistons. But as a general rule, all 1967-69 428 cranks are “N” cranks and not Armasteel.
The ’64/’65 421 HO Armasteel crank is #9773384. The ’66 Parts Catalog shows the #9782769 as the 421 & H.O. crank, so it was introduced a year before ’67. The RAII had it’s own specific crank casting, #9794054. It was marked Armasteel and was also used in the ’69 RAIV. The regular ’68 400 crank was #9773524, a nodular iron crank. I understand the machining difference, but it makes no sense to have the RA crank cast as “Armasteel” at the same time nodular iron cranks were produced if there is no difference except bearing tolerances.
The standard production and RA 1967-1968 400 cranks were an “N” crank, p/n 9773524. The 1969-1970 RA III crank was a “N”, p/n 9795480. The 1968 RA II (w/#96 round port heads) and the 1969-70 RA IV cranks were “N” cranks, p/n 9794054 with .001″ more clearance than standard. I observed the “N” on a RA IV crank from a disassembled 1970 RA IV engine.
If the crank was a 1968 428 engine it could be either a Armasteel #9783737 421 crank or a “N” crank, #9782769,depending on the production date. The latter is considered the 428 crank and were used in all the late production 1968 and 1969 428 engines.
The p/n 9783787 is correct for a 1964 Armasteel “421” crank. The #9773384 Armasteel crank was introduced in the 1965-1966 engines. Either of those cranks could have made it into some 1967-1968 “428” engines even after the #9782769 428 crank was introduced in 1967.

• “FS” = Forged Steel
• “AS” = ARMASTEEL  = PMI
• “PMI” = Pearlitic Malleable cast iron. ARMASTEEL logo may not be present on all cranks.
•  ARMASTEEL is not steel, but a form of cast iron.  ARMASTEEL  was a registered trademark (#0393916) GM used starting October of 1937. The trademark was last renewed in 1982 and expired in 2002.
• “N”  = Nodular Cast Iron. “N” mark may not be present on all cranks.
• “CFD” = Central Foundry Division. May not be present on all cranks.
• It appears many cranks do not have a casting date.
  • The normal GM format:  A=January, B=February etc. Second digit or digits is date, last digit is year. D124 = April 12, 1964 or 1974. 
• Some cranks may have a 3 digit number like 205. It may be a Julian production date, but there is no confirmation of that.

Armasteel

Armasteel casting

CFD casting

Stamped type number

N casting

Crankshaft Specification Table

Notes

FS

FS

FS

FS

AS

FS