Early 4.8L & 6.0L LS engines ( 1999-2000 ) have an extended crank flange that requires a specific flywheel.My 70 Z28 4-spd has the 168 tooth with the 621 bell.It is important …Always know your crankshaft register diameter. NOTES & EXCEPTIONS: Crankshafts for LT engines can be changed/swapped. The LS9 uses a special 9 bolt crank flange pattern.The LSA, LSX (aftermarket), and the new LT1 & LT4 engines have 8 bolt crank flange patterns.Series LS1,2,3,6,7 have 6 bolt crank flange bolt patterns.LS/LT series engines 1997-present (Gen 3, 4, & 5) All Big Blocks can use the 153 tooth flywheel when the engine block is drilled for starter type.They will accept the same flywheel as the early small-block engine with 2.485″ register diameter. All other big-block displacements used a 2-pc rear main seal, internal or “0” balance, and 168 tooth ring gear.engines were all 1-pc rear main seal and externally balanced. The early 454ci.the design used a 2-pc rear main seal and had its own specific balance.Engines will be either internally or externally balanced with the external balance being most common.In many cases, if you’re changing from one size to the other you will also need a new starter that is matched to that ring gear. 153 tooth and 168 tooth ring gears- many of the factory bellhousings will only accept the 153-tooth size, typically the aftermarket bellhousings will accept both sizes.1-pc rear main seal design crankshaft with 6 bolt flange & register diameter of 2.067″.Built from 1986-2003 for factory vehicles, still available through GM’s crate engine program.All had an internal or “0” balance EXCEPT 400 Small Block- which is externally balanced.In many cases, if you’re changing from one size to the other you will also need a new starter that is paired for that ring gear. 2-pc rear main seal design crankshaft with 6 bolt flange & register diameter of 2.485′.Gen III, IV, V LS/LT series engines feature only the large diameter, 168 tooth flywheels, and flexplates, but carry either a 6, 8, or 9 bolt crank flanges. Gen I and Gen II Chevy engines featured two available diameters of flywheels and two corresponding tooth counts of 153 and 168. These bolt patterns became successively smaller with each generation. Gen II (one-piece rear main seal), and Gen III, IV, V (LS style) are all different and will not permit any interchange between them. The crank flange bolt patterns of Gen I (two-piece rear main seal), GM engines are used in a wide variety of builds not just Chevys. You will want to gather as much possible information as you can before you set out on your parts-gathering journey so that you can find the right parts in one trip! Two engines might both be part of the “small block” family but are completely different when it comes to which flywheel they use. This is especially important because not everyone refers to things the same way. So deciding which engine to use is the first step. ![]() These are the critical elements to making sure you can properly attach your engine to your chosen transmission.Įach engine manufacturer has its own specific set-up.
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