Man, I hate asking dumb questions, but that's how I got through setting up my Eaton posi, full MSD ignition. changed lifters, set up my Avenger, etc...

My motor was created with a first generation big block. I currently have a TH400, but just ordered a kit to go to a TKO-600. I upgraded the clutch, so I will be getting a McCleod billet steel flywheel. Do I need to be concerned about harmonics and stuff? How do I tell if my motor was built internally or externally balanced? And if it's external, how do I know how much mass to bolt on the flywheel?

I would ask the motor builder, but it was already in the car when I bought it and don't know who to ask.

Thanks for any help. If this is the dumbest question in the world, on par with "how do I remove the air filter", I apologize.

gib,
There is really no way of answering this question properly. Do you have the flywheel / flexplate that was on the engine when you purchased it ? If so, your machine shop wshould be able to look at them and tell you if they are internal or external balance. 396's and 427's were internally balanced from the factory, 454's external. If it is a custom built engine, there is no real good way to tell unless you can get hold of the original builder. If your present flywheel has a weight on it, it is external balance. Any good balance shop should be able to spin it on thier balancer and tell you if it is the same as the new flywheel you buy.

Here is how you tell in the REAL world AND I have done this too!!!!!!!!!

I laid down on the ground on my back and stuck my head under the front of the engine and "fingered" the inside back of the damper to tell!!

A neutrally balanced 366/396/402/427 will be completely round and smooth back up in there IF stock whereas a 454/502 will have dog-knot b/c of the external, (i.e., Detroit), balance.

Hope this help's and the guy was trying to sell me a 454 until I told him it was a 402 P/U motor!!!

pdq67

My motor was created with a first generation big block.
To me, the first generation Chevy big block is the 348/409 "W" engine. Is that what you have?

I'm expecting you have a Mark IV (Gen 4) big block--the ordinary, common 396/402/427/454.