Originally Posted by 83 sierra classic
Thanks guys. Im still learning alot of this stuff but all I know is my engine has an external weigh on the crankshaft where the flywheel bolts up. On the donor truck it does not. My engine is a 350 as is the donor truck and both tooth counts on there flywheels are 168. Also both starter look exactlly alike.
The 1986 - up SB Chevrolet V8/4.3L V6 engines with a one-piece rear main seal use a 168 tooth counter weighted flywheel and use a starter with off-set starter bolts. The flex plate counter weight is to compensate for internally balanced engine that uses a one piece main seal crank flange that does not have a counterweight.
The 153 tooth flex plate has a 3.58" crank flange bolt circle and the 163 tooth flex plate has a 3.00" crank flange bolt circle. The smart fellers at the factory made them that way so they would be mechanic proof.
I don't know what 3-bolt torque converter bolt circle is used with the different transmissions. I used a TCI flex plate with 10.750" and 11.000" torque converter bolt patterns on my 1991 S10 Blazer 4.3L V6 with a 700R4 transmission which was 10.750"