ratflinger

Engine is internally balanced 396 SB. Harmonic balancer is neutral balance, but flexplate (GMPP 14088761) has a weight on it. Why? Summit lists this a HD replacement for stock and their description lists this for internal engine balance, external balance style. What gives?

jackson

All ... repeat ALL one-piece rear main seal SBC motors have a "hybrid" balance when OE ... damper is neutral but ALL OE 1pcrms SBC have a counterweight on rear. You can take the weight off but if assembly was balanced w/ wgt ... then you know what'll result... right? Do you KNOW it was internally balanced ... what does shop say that balanced motor? I'm not aware of source that sells 1pcrms sbc flexplates that do NOT have a weight.

ratflinger

Rotating assembly is an Eagle internal balanced kit & the machine shop checked and verified the balance when they assembled the short block. If the weight doesn't matter then OK, but I don't want to be hanging unnecessary weights on a balanced engine. I have seen neutral balance flexplates offered at Summit. It puzzles me as to why a weighted flexplate would be hung on an internally balanced engine.

jackson

Because ... 1pcrms are NOT true internal ... they're a hybrid. Why GM didn't go to the trouble to strengthen the block while they were lightening the design ... so that larger crank counterweights would fit inside ... was ... I'M GUESSING ... not cost-efficient. Ask the shop ... did they use a stock OE-type counterweighted flexplate to balance ... or factor for it? Verify it! Get it wrong & you won't be pleased.