406 balance ?

[ScotI]

I'm hoping someone can help me w/this. I picked up a 406(8) shortblock & I'm trying to complete the assembly.

The problem is it has an aftermarket crank (supposed to anyway), speed-pro hyper pistons, & 5.7 PM rods (the P/N for the pistons shows they're intended for 5.7" rod 400's so I'm hoping everything else is what it should be).

Can aftermarket 400 cranks come both internally/externally balanced? How do I know what balancer (and flexplate)to get? I'm considering bringing what I have to a machinist to verify everything is what it's supposed to be & having them balance everything because I'm paranoid it will self destruct otherwise.



What would you do?

[Kenova]

I've seen aftermarket cranks for the 400SB in both internal and external balance. I'm not 100% sure, but I think most of the externally balanced cranks are cast. Most of the forged cranks I've seen seem to call for internally balancing the assembly.
I can only think of two ways to be sure. The first is to disassemble the engine and have it checked at a shop that does balancing. The second way is to toss on a dampner and flywheel (internal or external) and wind it up. If you have the wrong dampner/flywheel hanging off of the crank you won't be long finding out!
You could try posting your Question at http://mikestarkcfm.proboards21.com/index.cgi Some of the guys there are right into the engine building business.
Ken

[Chevyman73]

It is at least possible. I've got a Bryant crank in my 421 that's internal balance. It could have even been exernally balanced and then rebalanced with mallory metal. A give away to that would be the welded in plugs of metal. Since its an aftermarket crank you should see the manufacturers name and part number on the first counter weight. If you can find it you could just look it up in a cartalog or call the manufacturer. If nothing else works have a good machinist recheck it. Better safe than sorry and cleaning up engine nuggets.

[Q ship]

From everything I've seen, 3.75"stroke cranks that internally balance require 6" rods to clear the larger weights, or a lot of heavy metal. I would think yours is external balance, but the only way to know is to take it to a good shop.

[ScotI]

Thanks guys. I'll flip it over on the stand & see if I can find a manufactures' ID or P/N. I had to do that for the pistons but didn't think the crank would have anything.