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Canadian Poncho Homepage -> Canadian Poncho -> 65-70 Full Size Power Train Tech Forum -> GM Flexplates
Post Info TOPIC: GM Flexplates
4SPEED427


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GM Flexplates
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I learned again today, never say never....

My friend is working on a car with a 454 that kept breaking starter noses, and I mean breaking them completely. 

I stopped at his shop today to say hi and he showed me something I've never seen. 

So of course a 454 using an externally balanced flexplate. He showed me the flexplate he removed from the 454. 

As many of you know, 454 always used the large flexplate (14") with 168 teeth. 

This engine had a 14" flexplate from who-knows-what with 139 teeth. So of course, the spacing on the teeth (139 tooth) doesn't match the spacing on the teeth (168 tooth). The drive will always try to fit into the correct spot but can't because of the spacing. 

He believes the flexplate (which is externally balanced but bolts right up to the 454 crank flange) is from a very early GM auto trans vehicle, possibly in the 50's and possibly a 6 cylinder. Anyone?



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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
DonSSDD


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Pre 1963, all flexplates were the 168 tooth, pretty sure all the way back to the 55 sbc.

 

Id wonder if anything older was externally balanced? It has the GM bolt pattern, anything weird about the bolt pattern? Maybe someone put the wrong ring gear on a bb flexplate? Truck or industrial use something or other?



-- Edited by DonSSDD on Friday 23rd of August 2024 05:37:33 AM

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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC.
1963- Pontiac top selling car in Canada

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DonSSDD


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Searched, summit sell an external balance 139 tooth for a 6.2L GM diesel.

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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC.
1963- Pontiac top selling car in Canada

Mahone Bay, NS Still not old enough to need an automatic
4SPEED427


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DonSSDD wrote:

Searched, summit sell an external balance 139 tooth for a 6.2L GM diesel.

 Exactly! I should have posted again later on after I did some reading. I found that also and texted my friend last night to tell him he likely has a 6.2/6.5 flexplate.



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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
DonSSDD


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Why bother making a different flexplate and starter?

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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC.
1963- Pontiac top selling car in Canada

Mahone Bay, NS Still not old enough to need an automatic
4SPEED427


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Strictly a thought but because the gas torque converter only used 3 bolts and the diesels used 6 I believe, maybe the converter hole spacing or size was not the same? And because the teeth count is less (139 vs 168) you can see the teeth are thicker on the diesel, making them stronger. Seems to me the diesels are around 22 to 1 compression, so maybe the 168 flexplate teeth are too thin for the extra cranking load?



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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
DonSSDD


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Makes sense and the fewer teeth would have spun faster depending on the number of teeth on the starter? Maybe a reduction starter too?

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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC.
1963- Pontiac top selling car in Canada

Mahone Bay, NS Still not old enough to need an automatic
Nov 18 to Dec 2 Black Friday UP TO 50% OFF Plus Huge Coupons
Nov 18 to Dec 2 Black Friday UP TO 50% OFF Plus Huge Coupons
4SPEED427


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I'm going by memory here so someone who knows better may correct me but I recall the 6.2 starter being a direct drive unit that looks similar to the gas unit only heavier duty. Certainly the drive is different because when you see the 6.2 flexplate laying on top of the gas flexplate you can sure see why it kept breaking noses (plus it was very noisy cranking the 454).



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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
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