How can you tell and internal balnce 454 from an external?
 

I have a mid 70's 454, #3999289, numbers come up as a 72-78 2 bolt truck motor. I put on a counterweighted flywheel for an external balance and it vibrates like crazy. This is the type of flywheel I have .
http://www.gmgoodwrench.com/perfpart...3827_large.jpg

I think it may be the wrong one.

Is there a way to tell if I have an internally balanced 454?

There is no such thing as an internally balanced 454, from the factory. *I* have never heard of an internally balanced 454 in the aftermarket, either. You could have a 427, which IS the same bore and internally balanced. I don't see any counterweights on the flywheel you have pictured. 454s are externally balanced at both ends. Reach around, with your finger tips, to the inside of the damper in the front. If it is there, you can feel the counterweight by the difference in the diameter of the ID of an unbalanced damper. If you can tell the stroke by inserting a piece of wire or something else through a spark plug hole, the 427 has a 3.76" (3 3/4") stroke and the 454 is 4.00".

RACE ON!!!

:iagree: I agree with everything except the part about their being no counterweight on the flywheel pictured. It has a big counterweight at the 12 oclock positon. That is the correct flywheel for a 454 not NOT a 427

Of course, I said, "I don't see any counterweights on the flywheel you have pictured.". If I squint my eyes, and tilt my head just right, I can either faintly see a counterweight at 12 O'Clock, or imagine one. However, it wouldn't surprise me, if in the past month, plus, he hasn't figured out the problem.

RACE ON!!!

All 454`s are externally balanced and the pictured flywheel is correct for a 454. However the balancer also must have a weight on it. To internally balance a 454 would require a ton of heavy metal to balance it and cost more than it`s worth. Especially on a two bolt main truck engine.