Originally Posted by wet_rat (Post 2812735)

I am getting contradicting info so please help me out. I have Gen VI blocks I need neutral flywheels for. SOme say the MK IV wheels won't work with Gen VI due to bolt pattern. SOme say the 1 and 2 piece main seal flange is different. Someone please confirm for a fact if the bolt patterns are the same and if there is any flange difference.

Originally Posted by Sport 280 (Post 2813181)

I do not know if this helps but according to Dennis Moore's book Big Block Chevy Marine Performance,
'Generation V (and VI) flywheels bolt pattern is the same as the Mark IV, the bolt patterns will physically interchange, however to accommodate the one-piece rear seal, the counterweight had to be removed from the flywheel flange. To keep the engine balanced, additional weight had to be added to the flywheel, making flywheels not interchangeable between one-piece and two-piece seal crankshafts. The extra weight added to the flywheels prevents them from being interchangeable with Mark IV flywheels.

Originally Posted by RHM253 (Post 2813360)

You should be able to use any sbc flywheel up 1985 except for the 400, and any 366 396 402 427 flywheel. All are neutral. Normally I like ballance the assembly with the flywheel I am going to use. I also like to balance the coupler bolted to the flywheel. I have seen a coupler out as much as 50 grams, and they are not always centered.

Originally Posted by Sport 280 (Post 2813703)

You also need to consider the harmonic balancer. The balancer for the 396 - 427s is neutral balanced. The 454 - 502 balancer has additional weight added for the externally balanced rotating assembly. If you are using neutrally balanced cranks, you need neutrally balanced flywheel and harmonic balancer. To be safe, I would have the complete rotating assembly balanced.