Flex plate choice ???

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jimjimjimmy

jimjimjimmy

lobsterman
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Had a noise and it was a broken flex plate i have no idea why it broke and it was sfi approved . 904 with an 3600 stall ultimate converter hooked to a internally ballanced 418 stroker .
What's everyone using ? i would like opinions why it would break it wasn't abused much and all the houseing and torque bolts were still tight no vibrations or anything.
 
jimjimjimmy said:
Had a noise and it was a broken flex plate i have no idea why it broke and it was sfi approved . 904 with an 3600 stall ultimate converter hooked to a internally ballanced 418 stroker .
What's everyone using ? i would like opinions why it would break it wasn't abused much and all the houseing and torque bolts were still tight no vibrations or anything.
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Check the crankshaft end play. A worn thrust bearing is one reason that could happen.
 
jimjimjimmy said:
Thanks i just checked , end play checked out fine . all four ears are broken off just inside the bolt holes .
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Did you double check the bolts are the correct diameter for the flex plate? If they are smaller than the holes, that could have caused it as well. It seems very unusual all four ears would "just break".
 
i agree Rusty , the bolts are the bigger 7/16'' arp bolts that came with the plate . I have been running this setup for about 12 years now without problem . There must be a reason or maybe it's at the end of it's life .
 
jimjimjimmy said:
i agree Rusty , the bolts are the bigger 7/16'' arp bolts that came with the plate . I have been running this setup for about 12 years now without problem . There must be a reason or maybe it's at the end of it's life .
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I just don't buy that. Not all four. Did you check to see if the converter has ballooned?
 
RustyRatRod said:
I just don't buy that. Not all four. Did you check to see if the converter has ballooned?
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That is what I was thinking, my buddies stroker, the converter balloned so bad it also took out the thrust bearing along with the flexplate.
 
Same thing happened to me - 273 and 904. This was a factory flex from 1974 with about 40k on it.
3:23 sg 8-3/4” if that matters.
I went SFI (TCI I believe from Summit about $100) and drilled and tapped the converter to 7/16” ARP.
No lock tite- I used their grease.
I used to drop it to 1st at like 25-30mph and hammer the throttle. Not anymore.
Been all summer and still no broken parts. My engine is tight too RRR :)

IMG_3796.jpeg
 
I've broken solid "ears" on the 4 ear SFI Mopar flexplates, but that's after a LOT of racing. I went to B&M solid round with no issues after that. I knew not to use OEM plates with cut-outs and was surprised the solid ear version broke.
 
jimjimjimmy said:
The converter looks fine
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I guess it's possible the flex plate just met the end of its lifespan. I find it incredibly difficult to believe all four ears gave up basically at the same time.
 
RustyRatRod said:
I guess it's possible the flex plate just met the end of its lifespan. I find it incredibly difficult to believe all four ears gave up basically at the same time.
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i was hopeing to find something wrong but all looks fine , i guess i will know more when i pull the engine .
 
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