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Old 02-28-2003, 10:55 AM
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Post balance for 400 sbc

I'm building a 409 out of a 400 sbc. When I had the bottom end assembled, the machine shop balanced the internals, I notice a large weld of glob in one of the crankshaft counterwhight. the same shop sold me a new balancer and flexplate for a 400. If he balanced the inside will I throw it off with this combo?

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Old 02-28-2003, 11:09 AM
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Balance and blueprint procedures do not affect the natural designed-in internal or external balance of an engine. You just end up with a smoother, tighter, excellent engine.
Is a 400 bored to what a 409, .030, .060?
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Old 02-28-2003, 11:29 AM
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[quote]Originally posted by pasadenahotrod:
<strong>Balance and blueprint procedures do not affect the natural designed-in internal or external balance of an engine....</strong><hr></blockquote>

Yeah Maybe, then again maybe not. Personally, I prefer to have the whole assembly balanced together. Most quality shops will want to have the damper and flexplate/flywheel in hand when balancing an assembly.
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Old 02-28-2003, 11:55 AM
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ok two good ansers. the 400 makes 409 when it is .040 over
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Old 02-28-2003, 12:03 PM
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You khow I have seen a shop show where they replaced each piston and rod with a chunk of metal the same weight as the assy. and connected to the crank journals with strapping tape and balance the whole thing. Don't quote me on the strapping tape. The idea was to balance the crank and rods and pistons outside of their bores.
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Old 02-28-2003, 12:25 PM
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Yeah. There are several different balancing methods. It's basically about matching the Rod/Piston weights, as close as possible, and balancing the crank so it spins true (simply put).
Think of it this way: If you have a perfectly balanced assembly (as in Pistons, Rods, and Crank), do you really want to take a chance and just put any Balancer and Flywheel on it? Or, would you play it smart, pay a few bucks extra, and balance everything? Technically speaking, a new Balancer and/or Flex Plate should aready be balanced, but we all know about assuming anything....right? The best answer is to ask the shop that balanced your assembly for advice.

[ February 28, 2003: Message edited by: Airport Towing ]</p>
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Old 02-28-2003, 02:06 PM
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why does the flexplate on a 400 have such a big weight on it? Ihave another guy telling me if i'm balanced on the inside I should use 350 or 305 flex, and harmonic. I need more input please. <img src="confused.gif" border="0">
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Old 02-28-2003, 02:40 PM
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I've got both a 383 and a 400. Both were balanced. My shop used the crank, rods, pistons, rings, bearings, balancer (400), and the flywheel (400). I always use the 400 style balancer. There is the possibility of an internally balanced 400 assembly but that involves $$$ and a special type welding.
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Old 02-28-2003, 06:39 PM
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your balance shop probably used the standard factory balance figure to compensate for the stock flywheel and balancer, if your crank is truely internally balanced they would have used "Mallory Metal" (tungstun)and if they did your total price would have been quite a bit more than a standard balance job.
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Old 02-28-2003, 07:25 PM
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Gaino,

I think you are misuderstanding internal balancing, external balancing and precision engine balancing. Typical 400 small blocks are use counter weights on the flexplate/flywheel and harmonic balancer instead of heavy counter weights inside the engine. They can be internally balanced by adding heavy metal to the crankshaft counterweights.

Now there is also engine balancing involving perfectly matching the piston rod weight to the crank counter weights. If this is done, your machinist will drill and/or weld on the counter weights to get a perfect balance between all parts. This process can be done on an externally balanced engine. I think this is what your machinist did.

You should be fine.

Chris
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