The flexplate that originally was bolted to this convertor in question.
Also was the original engine a 1 piece or 2 piece rear main seal engine?
CK5
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454 Swap
- Thread starter The1980BEAST
- Start date
The flexplate that originally was bolted to this convertor in question.
Also was the original engine a 1 piece or 2 piece rear main seal engine?
The1980BEAST
1/2 ton status
14" same size as the one on it now. the original is from a 305.
I'm trying to rule out certain flexplates so now just let me know if it was a 1 or 2 piece rear seal engine. Regardless there is no flexplate that has an 11" bolt pattern so your measurement has to be off either way slightly.
The1980BEAST
1/2 ton status
How can I tell? It was a 305 out of a passenger car. Can I tell from the flexplate?
Measure across the crank flange bolt holes and let me know if it is 3" on center or 3.58" on center for opposing holes farthest away from each other.
The1980BEAST
1/2 ton status
3.58
Ok, so now we've discovered that the engine was 100% for sure 1985-earlier and with that info there is only 1 flexplate possibility. The only flexplate it can be (the original that was bolted to the convertor) is a GM 471598 and it had a dual bolt pattern of 10.75" and 11.50", is 14" diameter with 168 tooth, and for internal balanced engines.
GM does not show a dual pattern flexplate for a 454. The only GM flexplate that would match up with what i believe you have is a GM 14001992. This flexplate is 14" diameter, 168 tooth, and 11.50" convertor bolt pattern for use with 454 engines from 1970-1990.
The1980BEAST
1/2 ton status
which should be the same as what I have...except for externally balanced engines...
Yes. Have you double and triple checked that the convertor doesn't bolt to either of the bolt patterns?
The1980BEAST
1/2 ton status
Yes. I won't have the engine out untill later tonight to be able to check the flexplate but I have a spare 454 flexplate and I just measured. All the bolt holes within each patern on the 454 one are 10" apart. The ones on the old 305 one, one set is 10" apart and lines up with the 454 one the other set are 9 1/4" apart. The 9 1/4" ones are the ones that work.
How or where are you taking this measurement from?
The1980BEAST
1/2 ton status
There are 6 possible bolt holes for the torque converter to bolt to. Two sets of 3. The sets are in a triangle. So I'm measuring from Hole A from set 1 to Hole B from set one. So one edge of the triangle is 10" or 9 1/4". Kinda hard to explain
The1980BEAST
1/2 ton status
Old flexplate infront of new one
Yellow circles are the holes that line up, the yellow boxes are the holes where the it bolts up
The measurments are from Circle to circle and box to box
Ok, i drew this up on Mastercam.
The1980BEAST
1/2 ton status
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dang, cause its actually the secret to the universe.
The1980BEAST
1/2 ton status
Alright yes that picture is correct for the old flex plate.
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Ok, now i think i understand that the flexplate on the 454 has a 6 bolt pattern used with a convertor with 6 mounting locations and not a dual bolt pattern used with only 3 mounting locations.
This is the flexplate you need then. http://www.summitracing.com/parts/TCI-399473/Application/?query=Year|1985|Make|CHEVROLET&prefilter=1
This flexplate fits a 1985 454 with a dual bolt pattern for the convertor. I like the TCI flexplate because it is .035" thicker than a factory flexplate to help prevent it from cracking.
The1980BEAST
1/2 ton status
Ok, is there anyway I can tripple check this will fit my old convertor for the TH350c?
Not really, but if you are getting a measurement of close to 9.25" (9 1/4")from center to center on the mounting holes then that is a 10.75" bolt pattern. Measure from the very center of the convertor nub to the center of one of the bolt holes and it should be 5.375" (5 3/8")
