Makes me wonder who balanced the assembly, the damper and flywheel or flexplate should have been with the assembly at the engine balancer's shop.

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The shop that built the engine ordered all the parts . The rotating assbly came from Summit Racing and ordered as internaly balanced assembly. The eagle kit came with balanced crank , H beam rods Bearings arp bolts JE pistons and rings.They made the mistake and did not order a complete assembly that would have included the damper and the flex plate. They claimed that they had built many stroker engines and yet did not realize that the 400 sb chevy,s were externaly balanced to start with.

Reading into these forums for some time as well as owning 2 jetboats as well as a v drive flat I came across a topic of pump vibration. The person seeking help was stumped and went as far as dropping the pan on his 454 and checking his rotating assembly after I would assume ruling out his pump for sources of the vibration. A heads up to some people who own chevy big blocks as well as a chevy 400 sb. These engines have externaly balanced rotating assemblies. To the layman or newbe this means that the crankshafts , balancers , flexplate or flywheel are balanced as a unit and can not have interchanged components unless they are all rebalanced as an assembly. I ran into the same problem when I had my 400 stroked to a 434. The engine builder builder used my externaly balanced balancer from my stock 400 and put it on my eagle internaly balanced rotating assembly. When it went on the dyno for tuning the dyno people coild not fiqure out why the engine was vibrating so much that it almost shook loose from the dyno and managed to blow the water restrictor off the dyno. After putting three minds together and going over the parts invoices for a couple of hours we realized what was wrong. Ordered a neutral balancer and fexplate and problem solved . Engine made 540 hp. at 5700 and 560 ft lbs tq. @ 4900. You could have placed a glass of water on the intake at WOT during the pull and it would't have spilt a drop. So a warning to all rely on only the best to look after your build requirements.