GM Crankshaft Flange Differences Caution

For 1998-2005 GM 4.3, 4.8, 5.3, 5.7 and 6.0L Engines

The AERA Technical Committee offers the following information on crankshaft replacement caution for 1998-2003 GM 4.3, 4.8, 5.3, 5.7 and 6.0L engines. Design changes in the flywheel flange thickness have been made to some crankshafts used in the above-mentioned engines. This bulletin is being re-published with additional information.

The later crankshafts are shorter on the flywheel flange as seen in the listing below. These changes are due to the many different vehicle / transmission combinations being built by GM.

A flywheel spacer ring (GM Part #125635320) and a longer bolt set (GM Part #12563533) is required when using a thin flange crankshaft to replace a thick flange crankshaft.

If the crankshaft is being used in a standard shift application you also need pilot bushing (GM Part #12557583 or 12479894).

Years Liters Casting # Trans Flange
98 early 4.3L 236, 255 V-6 1.62 thick flange
98+up 4.3L 236, 255 V-6 1.500 thick flange
99-00 4.8L 312 V-8 M/T 1.250 thick flange
99-00 6.0L 215 V-8 1.250 thick flange
99-05 4.8L 482 V-8 A/T .857 thick flange
01-05 4.8L 482 V-8 M/T .857 thick flange
99-05 5.3L 216 V-8 A/T .857 thick flange
97-05 5.7L 216 V-8 .857 thick flange
01-05 6.0L 216 V-8 .857 thick flange
Note: These GM part numbers correct as of 12-18-04.
Notes: All GEN III crankshafts used in Camaro, Corvette and Firebird have a .857 thick flange and also have a freeze plug installed at the bottom of the pilot shaft hole. The 4.8, 5.3 and 6.0L don't have the freeze plug. The drilled hole thru the centerline of the 5.7L LS1 and LS6 crankshafts allows a path to balance crankcase pressure within the lower crankcase. Doing so has eliminated possible oil consumption when the engine is operated over 4800 RPM.
Caution: Early crankshafts use a flat reluctor wheel and late have a recess. Recess will work on all years. DO NOT use a flat reluctor on late applications as it will cause an engine misfire. The AERA Technical Committee