Swapping flexplates on 302 with C4

Feb 26, 2016
6
0
1
Byron Center, MI
#1
Hey all. I have a ‘73 302 that needed a transmission. It originally had a 157 tooth case fill C4. Being on a strict budget I happened upon a ‘78 pan fill with a 164 tooth bell priced right so I got it. Now I’m trying to figure out this:

1. Can I buy simply buy a new 164 tooth flexplate? I asked my engine builder and he said the flexplate that came with the motor (157 tooth) was balanced to THAT motor so I should only use THAT flex plate. Is that true?

2. If I must use THAT flexplate, I heard that I could simply mount a pump mount bell (157 tooth) onto my case mount (164 tooth). Is this true?

3. Which would be the better option?
 
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tos

SN Certified Technician
Apr 27, 2001
861
61
49
Cincinnati Ohio
#2
As an example, If it is a factory balanced flexplate of say 28 oz imbalance then you could use any other 28 oz imbalance. BUT if a machine shop balanced that whole rotating assembly together including the flex plate then he is right to a point. If they did balance the whole assembly then it would depend on how much material they had to add or remove on the flex plate to get it to balance.
 

rbohm

SN Certified Technician
Apr 12, 2002
6,417
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tucson,az
#3
tos is right. the factory doesnt balance every rotating assembly individually, they dont have the time to do that. so they get it close, and weight adjustments are done on the crank. so any 28oz balance factor flexplate that matches the bell housing will do. so find a 164 tooth flexplate that use the same balance factor as your engine does and you are good to go.

as for a machine shop balancing the rotating assembly, once again they change the weight on the crank, not the balancer or flexplate/flywheel. the reason there is so that if you have to replace either of those items, you dont have to rebalance the engine rotating assembly as long as you again use the proper balance factor for your engine.
 

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