flexplate mayhem. Frustrated & questions...

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Here's the scenario- sbc 400 with original GM crank... I have had flexplate problems with this engine for years. No flexplates that Ive ever had will fit over the center of the crank, except for a pioneer SFI approved.. The non-SFI approved pioneers will not fit, nor will any other brands Ive tried.. (tried a few, definately not every brand, and the first one that was ever on there, I Think was GM)..

Okay, its weird problem but not really the end of the world. I figure the crank wasnt machined to exacting standards & tolerances, from the factory. Otherwise, all these replacement flexplates would have fit. The pioneer SFI flexplate is really nice, and I dont mind the extra $$ for the peice of mind. The other problem that I have, and it seems to be a little more serious, is too much run-out at the ring gear (front & back, not out of round) .... I dont know anybody thats ever dealt with this, but a lot of people have said something about shims between the crank & flexplate. Anyone have anything they can add? It sounds fairly simple. I have a dial indicator I can use to check for runout & stuff, but I havent found anybody that stocks the shims. Im going to check a machine shop tomorrow & maybe summit or jegs.

Does anybody have the spec for the diameter of that hole on a 70's sbc400 crank flexplate? I will get a micrometer and measure it and Ill bet dollars to donut holes that its out of spec by a few thou.

Im real hesitant about taking a grinder to the inside diameter of the flexplate to make room for the crank to slide thru. But if it comes down to it, I will clearance it.

anybody have anything to say about this? Like I said, monday I will get a new flexplate and check runout. Oh- my reason for replacing the flexplate in the first place is that the starter chewed it up and its missing teeth now ... Wish me luck, Ill keep you posted.


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