I have a 89 Formula 350 with a 700R4 and I was wondering why is there a weight called a batwing on the flexplate? If a small block 350 is internaly balanced why is this weight needed and what would happen if I used a flexplate without it. I have had other formulas and I have noticed this weight on all of them so I know it is not used to balance the flexplate itself. Any info?

 

If you have a two-piece rear main crank to look at, you'll see it has an offset counterbalance weight built onto the back end. Since the one-piece rear main crank has a round end on it, the counterbalance has to be put on the flexplate. So, technically it is a combination of internal and external balance - the harmonic damper is not counterweighted like it is on 400 cranks, which are externally balanced on both the damper and flexplate/flywheel.

Without it, you'll have a nice case of the shakes.

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[This message has been edited by five7kid (edited September 27, 2001).]

 

Yes, now that makes sense. But would I get vibration at all RPMs? The reason why I guestioned on having a flexplate without it is; I just had my flexplate replaced by a trans. shop and now I have a vibration at 2000-2500 RPM. It does it in drive and in park and is not related to mph. So I thought maybe the trans shop installed a flexplate without the weight. I don't think they would have I guess all one peice rear main engines should have to use this type of flexplate. I guess I will have to check it out.

 

They had to use the right plate because the bolt pattern is different. They do make the external (383,400ci) flexplates for the 1piece main seal, maybe they put one of them on there?