Which flex plate?

[Bill Cleveland]

My 350 block casting no. indicates it is a "1995 or later Chevy Vortec truck" block (casting #10243880) and I am confused about which flex plate to use - internal vs external balance? Any thoughts on this?

[Dewey Burton]

I assume you are building this block , when you take it to have the rotating assembly balanced , you will need the flex plate and vibration damper that you are going to use...if I remember all 350s are internally balanced , 400s and 454s are externally ....

[Bill Cleveland]

I have ordered a 168 tooth internal balance version from Summit; I hope it is the correct one. My block/crank are 1 pc. rear seal. My mild stall convertor (1900 - 2100 RPM) will accept either bolt pattern.

[cooter]

if im not mistaken the one piece oil seal blocks require the flexplate that has a balance weight on it.. my two piece oil seal flexplate on my 1958 283 does not have said weight. im also running the larger 168T

[cooter]

this is for one piece oil seal.. see weight..

[Bill Cleveland]

Thanks, cooter. Actually, my block is the one-piece later style 350 block, but my crank is an early-style 2-piece unit. Thus I had to use an adapter from Speedway for the rear main seal. So . . . will I still need to use the weighted flex plate?

(Speedway's description of the adapter:
"Enables a rebuilder to install a 2-piece design crankshaft in a one-piece seal design block. Billet aluminum. Alignment tool required for installation. Uses a 1986 and later 1-pc rear main style oil pan and gasket.")

[cooter]

Thanks, cooter. Actually, my block is the one-piece later style 350 block, but my crank is an early-style 2-piece unit. Thus I had to use an adapter from Speedway for the rear main seal. So . . . will I still need to use the weighted flex plate?

(Speedway's description of the adapter:
"Enables a rebuilder to install a 2-piece design crankshaft in a one-piece seal design block. Billet aluminum. Alignment tool required for installation. Uses a 1986 and later 1-pc rear main style oil pan and gasket.")

You have asked me a question I don't know answer too. I do know that the two piece crank has an external counter weight next to flexplate.. An educated guess and I stress guess would be that it would use the flexplate for that crank beins they are designed for each other, not necessarily the block. The one piece crank has no external weight but a weight on flexplate its self, they also are a pair.. Best I can do my friend..

[Bill Cleveland]

Thanks anyway for helping me think through the issue; I think I'm on the right track, to be guided in my choice for flex plate by the crank, not the block. Therefore, I will use the non-counterweighted item for my "2-piece-style" crank.

[cooter]