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Old 12-23-2010, 03:33 PM   #1
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Stock LT1 flywheel balance weight Question

Hey Guys,

I checked around for this answer but couldn't find one...

I want to bolt a stock LT1 flywheel to my stock 1 piece rear main 350TPI for a t56 swap. I know the flexplate on the car now is balance weighted, and the LT1 stock flywheel is also balanced with a weight. Does the balance weight of the Lt1 flywheel need to match the balance weight of the flexplate for the engine to run smoothly?
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Old 12-23-2010, 04:17 PM   #2
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Re: Stock LT1 flywheel balance weight Question

I believe so. If the engine is externally balanced it need the counterweight to be the same as the flexplate and if the engine is internally balanced it needs to be neutrally balanced
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Old 12-23-2010, 08:25 PM   #3
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Re: Stock LT1 flywheel balance weight Question

Yes, they need to weigh the same. I don't know off-hand if they are the same as the LT1 used a different rotating assembly than the L98, possibly requiring a different counterweight.
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Old 12-24-2010, 12:34 AM   #4
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Re: Stock LT1 flywheel balance weight Question

Thanks for the replys, well maybe someone can pipe in that knows if the L98 counterweight is the same as the LT1.....
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Old 12-24-2010, 09:56 AM   #5
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Re: Stock LT1 flywheel balance weight Question

Quote:
Originally Posted by 89blues View Post
Thanks for the replys, well maybe someone can pipe in that knows if the L98 counterweight is the same as the LT1.....
I don't know if this will help, but I had a vortec 350, stock balance, with a stock balance, LT1/T56 flywheel, and it worked fine.
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Old 12-25-2010, 11:31 PM   #6
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Re: Stock LT1 flywheel balance weight Question

All 86-up production 305 and 350 engines can use all 86-up production 305 and 350 flywheels. The LT1 and LT4 had nothing different at the rear of the crank, nor the rear of the block as far as flywheels and bellhousings are concerned.
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Old 12-26-2010, 11:16 AM   #7
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Re: Stock LT1 flywheel balance weight Question

Since both the LT1 and the other 1-pc RMS 305s and 350s are all internally balanced, with just the last little bit of INTERNAL balance weight mounted on the flywheel or flex plate, they all balance the same.

Look at a 2-pc RMS crank flange sometime. You'll observe that it's a funny shape. That shape is the rearmost INTERNAL balance weight. But since the 1-pc RMS is yerbasic lip seal and therefore requires that the flange be round, that last INTERNAL balance weight had to be moved from the crank to the flywheel. It is the same amount of weight on all of those cranks.

The only SBC that is TRULY "externally" balanced is the 400. The short stock 400 rods do not allow the crank counterweights in the center of the crank to be large enough to completely balance the other stuff. "Internal" and "external" balance DO NOT refer to what the weight is fastened to, and this terminolgy should be avoided if at all possible, to prevent confusion.

ALL 305s and 350s (including the LT1 which is a 350 just like any other 350 in this regard) have the same balance, subject to the rearmost couple of inch-ounces being mounted on either the crank in the early style or on the flywheel in the later.
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Old 09-17-2011, 04:30 PM   #8
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Re: Stock LT1 flywheel balance weight Question

Im having vibration issues using a stock LT1 flywheel, Atleast that's what the seller told me, behind a sbc 350 1piece RMS engine...but the flywheel seem to have been drilled to fit the dial pin of the 1 piece RMS crank...do you think this could throw off the balance of the flywheel and will a LT1 flywheel come without the seventh hole?
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Old 09-29-2011, 01:32 AM   #9
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Re: Stock LT1 flywheel balance weight Question

Does it have a weight cast into it or otherwise attached on the back side?

No.

You might want to take that flywheel and a known-good '86-up flywheel to a machine shoppe and ask if they have the same imbalance built into them.
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Old 09-29-2011, 01:32 AM
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