I am replacing my 7.4L gen 5 motor with a 502 gen 6 crate motor. I want to use the marine flywheel off my 454. Do I need to rebalance the 502 with the marine flywheel or can I just bolt it up and go.

I believe they are interchangeable and because you are not running a HP motor I would think it would be ok.

There are others on this board with more expertise, lets see what they have to say.

PS How did you weather the Hurricane? I know you guys are further north, did you receive alot of rain damage?

Take a look in Dennis Moores book. He goes through all of the flywheel changes etc.. I think Gen5 and 6 are the same, with Gen IV being different. I can take a look when I get home tonight.

We got some high winds but not enough to do any damage. We got some nice rain...helped to keep our lakes full for lots of good boating.

Scott, I've looked through his book and have found nothing specific on the swap. Let me know if you find anything.

Just did the same swap 2 weeks ago, no problem in using your old flywheel on the Gen VI. If you have the flywheel off already, what are the numbers on the backside and I can confirm for you.

Gen 5 and 6 are interchangable. MarkIV is not.

The number on the flywheel is 10101171 N

The flywheel wont work because of the balance. It will bolt up but it will not be balanced. The 7.4 has cast pistons, cast crank, and small rods and requires a differently balanced flywheel than the 502 with forged componets. All modern big blocks are externally balanced by use of balanced flywheels and harmonic balancers. There are different part numbers for flywheels from a cast motpr such as the 7.4 and forged motors like the 502.

When I put a 502 crate in my last boat I was aware of this and ordered the correct flywheel from GM. If you have a GM performance Parts Catalog the one you need is the flywheel for a 502 for use with a standard transmission. The engine coupler will bolt on the new flywheel right where the pressure plate bolts on. Its the same flywheel that comes on a merc 502.

Ron