Proper flexplate/starter

[AH55]

Hey guys, got a couple of questions I need some help with. I have a Chevy 385, internally balanced with a one piece rear main. Well, I've chewed up 3 brand new starters this week, so I need to replace the flexplate just out of process of elimination. I've tried every combination of shims I can think of and it still chews them up so I'm guessing flexplate is bent or something, although I've never heard of that.

Well my question is, do I need a stock 400 flexplate (current one has weights on it) or a stock 350 flexplate? I was sure it was going to be a 400 flexplate due to the 400 crank, but now I'm hearing a 350 works also. also, does it matter between 153 tooth or 168 tooth. I dont have the one in it out yet so I havent gotten an oppurtunity to count the teeth. I have tried starters from an 86 silverado and a 95 silverado (high torque mini) and it chewed em both up, so hopefully its as simple as a bent flexplate. Thanks for your help.
Armond

[usafracer]

If you have in internal balance motor then you need the pre 86 chevy internal balance 153 tooth flex plate. Sounds to me that you also need to shim the starter but also a shim or two behind the flex plate.

[stpmotorsports]

flexplate

Pre 86 flexplate will not bolt onto a 1 piece rear main crank. All of the stock 1-piece rear main flexplates have a weight on them, this is to make up for not having the rear flange on the crank like the old ones did. They are still considered internal balance.
If it is a truly internally balanced crank, you may have to get a late 80s-early 90s camaro flex and knock the weight off of it. Best to go back to whoever balanced the engine and ask them what you need.

[AH55]

I have a correction. It is externally balanced. I was confusing balancing the rods and pistons with the crank. It's just an eagle cast crank that is not balanced. I got the flexplate off tonight and it does not look that beat up but I'm still replacing it. I read somewhere that they dont make a 400 flexplate for a one pc rear main, hope this isn't true. Thanks for your help.

[Egoracing]

I have a correction. It is externally balanced. I was confusing balancing the rods and pistons with the crank. It's just an eagle cast crank that is not balanced. I got the flexplate off tonight and it does not look that beat up but I'm still replacing it. I read somewhere that they dont make a 400 flexplate for a one pc rear main, hope this isn't true. Thanks for your help.

A factory one peice seal is external ballanced, all GM crate motors are one piece seals and are external. You need a newer 350 truck/camaro flexplate. This is NOT the same extarnal ballance of the 400 so it's parts will not work.

[parrot69777]

2 piece flywheels will not bolt onto a 1 piece seal cranks and vice versa. The bolt pattern is different.

All one piece seal flexplates/flywheels have a counterweight to make up for the flange missing on the end of the crank. This does not mean the crankshaft is externally balanced as the balancer is not counterweighted as well.

I have seen people put 2 piece seal cranks in one piece blocks with the use of a seal adapter.

[AH55]

Thanks alot for the help guys. All my buddies have 2 piece motors and I'm the "fortunate" one that ended up with a one pc. I've been told to get a one pc 400 flexplate but then found out the last 400 block was produced in '81.

So a one piece 350 flexplate it is. Thanks again guys.
Armond