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Discussion Starter #1
Hello all,

I was assembling a 80 302 and C4 for installation in my Fairlane when I discovered my aftermarket flexplate did not properly mate with my torque converter. Despite the flexplate having the correct tooth count, balance weight (28.2 oz) and bolt pattern, its face was too shallow to accept the torque converter, causing interference that locked up the engine and tranny when the bellhousing was tightened down.

So I replaced it with another flexplate with the proper depth. However, the engine rotating assembly was balanced with the balancer and flexplate, so now I'm concerned the balance will be wrecked.

I obviously don't want to tear this back down for a trip back to the balance shop. I've gotten conflicting opinions about whether the typical rotating assembly balance allows for the replacement of wear items such as the balancer and flexplate without re-balancing.

The flexplate (and balancer) did not have any material added or removed. However, the replacement flexplate is lighter guage steel than the one the engine was balanced with, but does have the correct 28.2 oz balance weight.

Any ideas/thoughts/experiences much appreciated,

Thanks Nate.
 

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as long as they didn't change the flexplate you should be ok... but a lot of shops will add or remove weight from the balancer and flexplate... they asked me if it was ok to add weight to my Bal. Flx. and I said no add it to the crank..that way I could replace either with a 28oz without any problems..
 

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by the way did you pull the bellhousing to the block with the bolts?? if so you might have destroyed the pump in your C4
 

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Discussion Starter #4
Thanks for response. I did not see any modification to either the balancer or flexplate after they returned from the shop, but did see where some weight had been added to the crank.

I did consider the unfortunate possibility of busting the pump gears, but I don't think the interference was quite that bad; the tranny could be manually pushed tight to the block without cranking the bellhousing bolts. I think it was just enough to take all the clearance out the transmission and make rotating it or the engine very difficult.

I'm still at a bit of loss as to nature of the flexplate problem though. I was not aware of difference in depth in 302 flexplates, just the diameter and balance weight.
 

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good chance you didn't have the converter all the way in the pump.. converter and transmission should be together before you bolt it up to the block... I have seen people pull and reinstall transmissions leaving the converter on the flexplate.. never works that way..

if it wouldn't turn over that's tight...
 

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Discussion Starter #6
Good thought, but that the converter was properly seated I am sure of. I checked it several times, including the straight-edge across the bellhousing method. It was properly installed in the tranny before I bolted the transmission up as well. The engine would turn by levering the flexplate with a screwdriver, but it was very hard to rotate.

The flexplate difference was measurable/observable, but the root cause of the difference, or if it is simply manufacturer error, I have no clue about.

Thanks again,

Nate
 

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Was that a Scat flex plate by any chance? I had a terrible time getting a Scat SFI approved flex plate to line up with the holes in the crank. They would not index in any position. Finally had to re-drill two and then, after everything was back together, the starter gear started knocking the teeth off of it! What a POS!!! I tore it all down, including having to remove the tranny of coarse, put a TCI plater on and everything is hunky dory sense. The company told me they would give me a new Scat plate but not refund my money. I told them where they could stuff the plate.
 

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Discussion Starter #8
This is the unit I got-

1830204 – Gold Series SFI-Rated Chromoly Steel Flexplate - PRW — Your Partner In Performance

-which was bought from an Ebay vendor. Yes, I know, caveat emptor, etc...

Notice the cross section has only one depression, while stock units have two, one for the crank bolt circle and one for the converter face. My problem was that the depression for the torque converter face was too small of a diameter to allow the torque converter to mate up to the flexplate without interference.
 

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what ever wheel you use . When case/bell is bolt to the block , TQ/Conv all the way back into trans .. min. pull up for the tq/c to wheel is about .150" (little more of 1/8" to 3/16" ) Have to ask , you got the starter locating plate between block and trans ?

'this a OEM tq/conv. ?

aftermarket/ rebuilt units . seen the neckto long
 

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Do you have the "Block Plate" in place?? I had a hard time finding one and I think it is about .060" thick......would that make a difference??
 

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Discussion Starter #11 (Edited)
Dan,

Thanks for the response. I am using the block plate between the block and bellhousing. The replacement flexplate fit as it should- With the transmission fully bolted up, there is a small amount of clearance that allowed the converter studs to wiggle freely in the flexplate prior to tightening down the converter nuts. The first flexplate did not allow any movement of the converter studs in the flexplate once the trans was bolted up.

Edit- The converter is an aftermarket Hughes unit (but obviously built from an OEM core), but again, with the replacement flexplate everything bolted up nicely so I think the converter is okay.
 

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Discussion Starter #12
Before I let this thread go away entirely- Any further thoughts on potential balance problems created by the replacement flexplate from you engine builders and machinist gurus out there?

Thanks again,

Nate
 

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Before I let this thread go away entirely- Any further thoughts on potential balance problems created by the replacement flexplate from you engine builders and machinist gurus out there?

Thanks again,

Nate
you are good to go . balance shop didnt add or remove weight from oem balance . replacement will be the same
 

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where did you get the flexplate that worked? What was the part number. I am also connecting a 302 (1972) to a C4 and need a larger toothed flexplate.
 
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