This is for a external balance only, for internal I think 1 and 2 piece seal flywheels interchange just fine.

The amount of mass may be slightly different, but it wouldn't be in a different spot. If the entire assembly is being balanced, it can be corrected. Either on the flywheel itself, or the crankshaft.

My short block just got finished today, I will pick it up tommorrow. I have a two piece flywheel and a new one piece flywheel there, so when I pick it up I will look. My engine builder is pretty darn sharp on BBC and he didnt make anything off selling me a new flywheel, and he said they did not interchange. I will look tomorrow and see why.

If it bolts to the back of the crank, it can be corrected to work. When making corrections on a flywheel, you're working at about a 7 inch radius... this has a much greater influence than corrections made at the crank counterweight. You could put a neutral flywheel off a 350 small block on there, and drill a series of holes opposite the location where the cast weight would be, and achieve the same thing. I've had to do it a few times in 24 years of running my Hines engine balancer. :cool-smiley-011:

just buy a new one and be done it has a brand new ring gear too http://www.jegs.com/i/GM+Performance...6987/10002/-1#

mrfixxall
 

if he stated you need to change the flywheel then what about the harmonic ballancer? my machine guy said the only time you need to change the flywheel(454/502) is when you internally ballance a motor with 6.385 rods.. sounds fishy,unless your flywheel was all rusted up and he didnt want to use it

the back of the cranks on the 454 cast cranks are different from the 502 forged cranks

Im not sure if the 454 forged cranks are the same as the 502,

i think the weight on the flywheel between what came on the cast crank is different from what came on the forged crank

mrfixxall
 

i have done several conversions,454 to 502/ 502 to 454 and have had no issues except going from mark to gen 5 & 6 stuff..


on the higher eng merc stuff their machined out of a hunk of metal (billit steel) and the more commin 454/502 is a cast iron flywheel..he may have wanted you to have a stronger flywheel for your allpication..