400 flywheel on a 350 and vise versus - Chevelle Tech
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post #1 of 6 (permalink) Old Mar 26th, 99, 2:05 AM Thread Starter
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400 flywheel are balanced, right? 350's do not balance the flywheel right? What is the harm in putting a balanced flywheel on an engine that doesn't need a balanced one? I was told that I could use a 350 flywheel on a 400 if I had it balanced. Does it work the other way too? I ask because I ordered a custom flywheel for my car and it has some metal removed form it in various places. I am assuming that this means it is balanced. I told the shop my application and I assume they are compitent and know what they are doing. I hope this is not a problem. I don't think it will be. Let me know if I'm wrong.

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post #2 of 6 (permalink) Old Mar 26th, 99, 3:52 AM
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400SB and 454BB are externally balanced engines. That means that both the flywheel and the harmonic balancer for these engines are designed to be out-of-balance. In other words, Chevrolet couldn't find space inside the crankcase for large enough balance weights on the crank so they put some of the balance weight externally on the flywheel and harmonic balancer. Good balance shop can sort all this out.

Fred Aldrich
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post #3 of 6 (permalink) Old Mar 26th, 99, 11:01 AM
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In other words, the 400/454 flywheel has counterweights built into it, thus by itself is NOT balanced, but when properly installed on the right engine, the entire assembly is balanced. All other flywheels ARE balanced by themselves thus are interchangeable.

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post #4 of 6 (permalink) Old Mar 26th, 99, 11:33 AM
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ALL SB(except 400) & BB (except 454) flywheels are "neutral" balanced. SB400 & BB454 flywheels have, as has been mentioned, an additional counterweight.
If you are building a 400 or 454 and DO NOT have the counter balanced flywheel, you have 2 choices. You can pay extra to have the engine INTERNALLY balanced, or, you can use a large diameter (14in) flywheel (these flywheels are common) and have additional weight REMOVED from the opposite side.
Now, if you have a 400/454 flywheel and are building a 350 or 427BB, DO NOT use it and have the counterweight removed! These flywheels are somewhat scarce and you need to save this flywheel for use on a SB400/454BB----------------or sell it to me.

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post #5 of 6 (permalink) Old Mar 26th, 99, 12:14 PM Thread Starter
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I am building a 350, so the flywheel I got is fine. It appears balanced, it has material removed at various points. It is a custom 153 tooth flywheel, I can't use the 14" flywheel with the T56 I'm putting in the car. The bellhousing is too small.
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post #6 of 6 (permalink) Old Mar 26th, 99, 6:13 PM
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Hi guys,
I would just like to add that all of the above changed in 1986 when Chevy switched to the one piece rear main seal type crankshafts. The one piece seal 350's and 305's are also require a flywheel that has a weight on it. The same is true for the new Big Blocks, and they confuse the subject even more by using a different flywheel weight for cast and steel cranks ! If you are not absolutely sure, ask a local balance shop for help !

Bill Koustenis
Advanced Automotive Machine
Waldorf Md
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