60 Degree V6 Crankshafts

With the introduction of an all new V6 engine GM had to give this special engine a new crankshaft. The first 60 degree V6 crankshafts were all cast nodular iron. The 6 crankpins and the 2 center main feature deep rolled fillets making the crank very durable. The early cranks from 1980 until 1986 are all externally balanced, meaning they require additional weighting on the rear flexplate/flywheel to achieve a balanced assembly. The rotating assembly must be balanced with the flexplate/flywheel attached. Early cranks can be brought into internal balance by adding Mallory weights to the rear counterweight and using a neutral balance flexplate/flywheel. In 1987 some S-10 and Camaro's still used an externally balance crankshaft. 1987 was the first year internally balanced crankshafts were introduced. The addition of a reluctor wheel into the center of the crankshaft and the addition of a counterweight between the number 5 and 6 rod journals provided the needed mass for the crankshaft to be internally balanced. The reluctor wheel was machined with notches which provided the signal for the crankshaft position sensor. In rear wheel drive vehicles the reluctor wheel was not machined with notches because it was not required for the fuel delivery and ignition system.

Early production crankshafts use 63.35mm (2.494) main bearing diameters. For comparison the first Small Block used 58.42mm (2.30") main bearings later changed to 62.23mm (2.45") in 1968. Even with main journal diameters larger than a Small Block the 60 degree V6 was still prone to bearing failure. Beginning in 1985 the main bearings were increased in size to 67.25mm (2.648"). When selecting a crank for rebuild or replacement always seek out the later cranks. All fuel injected engines in 1985 have large main bearings but some S-10's in 1985 may still have small main bearings. In order to use a large main journal crankshaft the engine block must also be of the same style. All crankshafts since the beginning of production used a 50.7mm (2.0") crank pin diameter, the same as early Small Blocks.

The first crankshafts used in 2.8L engines had a 76mm (2.99")  stroke. This stroke would remain the same until the 3.1L appeared in 1989. The stroke in the 3.1L was increased by 8mm (0.315") to 84mm (3.307"). This size of crankshaft would continue all the way through to the 3400 motor. The crank was never changed after 1989 until the 3500 motor was introduced.

Several internally balanced crankshafts featured lead in grooves on the number 2 and number 3 main bearings. These lead in groves help increase oil flow to the rod bearings. Some 1987 or later engine without lead in groves have a crank with modified oil holes that do not require lead in grooves to provide adequate rod bearing lubrication.

In 2004 GM introduced a 3.5L engine that saw an increase in the bore to 94mm (3.70") but the crankshaft retained the 84mm (3.307") stroke. However this new crank was forged in some applications and can be identified by its rougher shape and wide parting lines. The other interesting feature was its large 57.125mm (2.249") main journals which would allow for offset grinding to increase the stroke of an engine when using rods for a 50.7mm (2.0") rod journal. This new crank saw the introduction of a new trigger wheel in the center of the crank. In applications where the old style reluctor wheel is required an external trigger wheel will have to be used. On applications that use a distributor then this change in design is not a concern.

Modifications to the stock crank are not necessary on stock or mildly modified engines. However for higher performance the regular slew of aftermarket crank modifications can be performed such and profiling the leading and trailing edges of the counterweights, lathe machining the counterweights to balance instead of drilling, polishing the casting to reduce windage and several coating options to shed oil and reduce friction. The stock cast cranks perform well in applications in the 400hp range and the forged 3500 version will handle almost anything you can make out of a 60 Degree V6.

 
Rod and Main journal locations

 
Cast in reluctor wheel on all internally balanced Gen I, II and III engines