balanced flex plate on balanced 360 cid

R BEE said

Sorry I wasn't more clear . Let me try again with my 52 year old brain.
The motor was used as a late model race engine running circle tracks throughout New England It was designed to run at 7500-8000 rpm's.
It was internally balanced and externally balanced. By saying heavy on the cam I meant high lift and does shake some. As for punctuation sorry
but you get what i have to offer.Thanks for Reply

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Ok Bee. The cam comment threw me but I understand now. Here's the thing, an engine can't be internally and externally balanced. Has to be one or the other, no iff's and's or but's. Using the B&M flexplate designed for an externally balanced 360 combined with a fluid damper (balancer) may be the issue because the B&M plate is for an externally balanced engine and most fluid damper's are for internally balanced engines, if they are for an external balanced engine they need to be for that specific engine as different engines require a different ammount of balance weight. Like Brian T asked what were you told you needed to run for a flexplate and balancer when you bought the engine? Was either the flexplate or balancer you have on it now on it when you bought it? If I were you I wouldn't run it anymore than needed for testing purposes (no more burnouts for sure) until you have the vibration solved. A harmonic vibration like you described can wreak havoc on engine and trans. components. I've seen cranks, torque converter snouts, and trans. input shafts snapped right in half because of a harmonic vibration. At the least it'll take a lot of life out of the bearings.