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Old 02-18-2010, 12:24 PM
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Converting SBC External Balance to Internal Balance

The other day I was going through the price sheets for my recent build sbc 350 and came across the one from the machine shop. He wrote down internal balanced. The crank and block are a 1pc from a 1991 pickup which i believe are from the factory externally balanced.

I wanted to make sure he balanced it correctly i called him up and he said the balance was almost dead on, it was indeed internal and he only charged me $100. I reused the stock crank it was ground .010 on the mains and rods. Eagle I beam rods and Keith black flat top hyp pistons. Speed pro rings. I am running a neutral balance flexplate because the motor had a flywheel on it when i got it.

So my question is can an externally balanced rotating assembly be converted to internally balanced by running a neutral flexplate and very little balancing.

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Old 02-18-2010, 12:35 PM
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which i believe are from the factory externally balanced.
Nope,... Your motor is known as an Internally balanced motor....

Only the old 400 SBC were Externally balanced....
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Old 02-18-2010, 12:42 PM
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SBC is internally balanced

but to answer can a externally balanced motor be change to internal by going to a nuetral flywheel/flexplate and very little mallory metal added to the inside , No its going totake alot of mallory metal to be added it mostly depends on what your bob weights add up to be , but you will net to change to th nuetral flexplate/flywheel and a nuetral dampner to make it internally balanced , easiest way to identify a external balanced motor is look at the backside of the dampner theres either going to be a cutout on one side or a bunch of metal offset to oneside by the hub ( and certain fords they actually have bobweights that slide on the crankshaft )
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Old 02-18-2010, 01:02 PM
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I believe the 1 piece seal engines use a neutral balance damper up front and an externally balanced flywheel/flexplate at the rear because of the different style crank flange.
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