Curious... balancing a SBC 400 vs other SBC's - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 05-03-2002, 10:22 AM
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Curious... balancing a SBC 400 vs other SBC\'s

I'm curious... I've heard it mentioned a bunch of times that SBC 400's are externally balanced. All other SBC's are internally balanced. I know from my experience building 350's in the past, you balance the rotating assembly by weighing the connecting rods and grinding the caps until they all match the weight of the lightest rod (there's more to it than that but that's the gist of it).

How are 400's balanced "externally"?
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post #2 of (permalink) Old 05-03-2002, 11:26 AM
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Re: Curious... balancing a SBC 400 vs other SBC\'s

hmmmm I know this, ohhhhh dang its on the tip of my tounge, I think they have an external flywheel. alright thats all Im gona say cause after saying that Im not so sure. someone else will know

Evan
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post #3 of (permalink) Old 05-03-2002, 12:51 PM
 
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Re: Curious... balancing a SBC 400 vs other SBC\'s

I believe that there is not enough room to balance the 400 with the crankshaft counterweights alone (due to it's longer stroke) hence the weighted flywheel and notched harmonic balancer
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post #4 of (permalink) Old 05-04-2002, 07:32 AM
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Re: Curious... balancing a SBC 400 vs other SBC\'s

Matching the weight of the pistons and rods is just part of it. After that, you take the weight of a piston, rings, pin, and the top half of the rod to get your bob weight. The crank is put on a balance machine with the dampner and flexplate installed. It is spun at around 500 rpm. The crank is balanced one half at a time. Balance can be adjusted by drilling out counter wieghts to lightnen or by drilling a hole in a counter weight and installing heavier metal slugs in the hole, mallory the metal is. It is expensive. Doing it this way you could balance a 400 crank internally. Stock car guys do it due to the type of direct drive or small clutch set up.
post #5 of (permalink) Old 05-04-2002, 08:46 AM
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Re: Curious... balancing a SBC 400 vs other SBC\'s

Yeah, anything but a 400 usually gets the balancing done by drilling holes in the crank. I've never had a crank that didn't look like swiss cheese from the factory. I know what you mean by grinding caps but that is to match the rods. Some guys match the pistons by grinding the inside of the piston also. The crank is usually balanced separately and they drill holes/add weight with some weird kind of metal (at least I think it's metal). "Real" high performance shops can balance everything at once but we're talking some serious money to have this done.

I've only seen a couple 400s in my life and I wish I could find one to buy. However, I can see why they're externally balanced. They've got a big crank and not much room to balance so they stuff a huge-assed harmonic balancer on the front of it and use that for more material to balance off. I've been told that you can balance off the flexplate/flywheel but that seems kind of stupid to me because they aren't the strongest thing in the world.
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post #6 of (permalink) Old 05-04-2002, 01:10 PM
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Re: Curious... balancing a SBC 400 vs other SBC\'s

I have a 400 block. It is already .030 over and needs to go .060. No crank and rods (at least i don't think i have them, but i might) Let me know if you are interested.
post #7 of (permalink) Old 05-04-2002, 01:46 PM
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Re: Curious... balancing a SBC 400 vs other SBC\'s

Well, how much do you want?

I'll be in downstate Michigan next week. It's a two and a half hour drive to Fort Wayne but I don't know where your city is.

thanks
-Brian
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post #8 of (permalink) Old 05-05-2002, 12:25 PM
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Re: Curious... balancing a SBC 400 vs other SBC\'s

Do you have any small block stuff laying around to trade? (I could use a 350 block) Or anything that might interest a gizmo/truck guy? I am about 1 hour south west of indy, Terre Haute IN.
post #9 of (permalink) Old 05-05-2002, 01:06 PM
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Re: Curious... balancing a SBC 400 vs other SBC\'s

Pretty much all my SBC stuff has a home except my 327 which someone would have to kill me to get ahold of. I mean, I have junk stuff like a pair of manifolds, a distributor (I think), and a dead TH400. I can probably find a carburetor or two in dire need of a rebuild. Pretty much all junk that I wouldn't want.

I just used expedia to see where that city is. It's a five hour drive from Lansing. Pretty long drive since I'll already have an 8 hour one from the U.P. of Michigan.


-Brian
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post #10 of (permalink) Old 05-05-2002, 02:45 PM
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Re: Curious... balancing a SBC 400 vs other SBC\'s

if you are interested I would take the th400 and distributor, I can always use more junk. I have always wanted to try rebuilding a tranny.
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