This is not an issue when working with original-configuration GM powertrains, but must be addressed when mixing different iterations of GM transmissions. Crank Flange Spacingĭifferent from their Chevy predecessors, most of the Gen III engines (see chart, below) had a shorter crank flange, offset of about 4/10' closer to the block. These bolt patterns became successively smaller with each generation. The crank flange bolt patterns of Gen I (two-piece rear main seal), Gen II (one-piece rear main seal) and Gen III+ are all different and will not permit any interchange between them. Gen III engines feature only the large diameter, 168 tooth flywheels and flexplates. Gen I and Gen II Chevy engines featured two available diameters of flywheels / flexplates and two corresponding tooth counts of 153 and 168. Ring Gears & Flywheel / Flexplate Diameters Of note, Gen III engines use metric M10 fasteners in place of the original 3/8-16 specification of its predecessors. It's generally recognized that there is no significant sacrifice in strength because of it, but many performance powertrain builders do choose to transfer punch, drill and tap this hole for maximum strength, obviously using exceptional care to prevent a crooked tap or excessively deep hole. With the recommisioning of this bolt hole, GM closed off the bolt hole at the ~1:30 o'clock position in the block. Interestingly, this bolt hole had been used on earlier Chevy V8 applications, but had become just a vestigial, untapped boss on these block castings through the latter portion of the Gen I & Gen II era. Generation I & II Transitioning to Generation III Block to Bellhousing Bolt PatternĪs mentioned above, the block bolt pattern was largely the same, and the locating dowel positions and diameters were fully identical but GM engineers opened up the bolt hole on the LS / Vortec blocks at the 12 o'clock position, as viewed from the rear. Ford 1.8L - 2.5L 'Pinto' Engines into the Jeep.Chevrolet, Buick & GM Engines into the Jeep.

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