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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old March 8th, 2023, 10:12 PM
arepoff arepoff is offline
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Default Internally or externally balanced?

I am in process of building a 478 for my K1000. Need to know if the engine is internally or externally balanced. I have to figure out a flywheel to bolt to a light truck tranny. I know others have done this with a custom flywheel but I can't find any info. If internally balanced I thought about having the 478 flywheel turned down the the smaller diameter and installing the ring gear. Any help appreciated. Thanks.
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  #2  
Old March 9th, 2023, 07:15 PM
Prowbar Prowbar is offline
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Default Re: Internally or externally balanced?

Nice to hear, a fellow 478 swapper
The 478 is externally balanced, in the front pulley and flywheel. Take a look at my 478 build thread, I am converting my 478 flywheel to work with the light duty bellhousing and clutch.
For the front pulley I'm planning on making a bolt on weight to use the 305 pulley. The 478 4 groove pulley will not work with the light duty timing cover.

Read through my build thread, lots of questions are answered there.
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Old March 9th, 2023, 09:34 PM
arepoff arepoff is offline
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Default Re: Internally or externally balanced?

Thank you. I will check into your thread. I have everything sorted except for this piece.
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Old March 9th, 2023, 11:45 PM
arepoff arepoff is offline
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Default Re: Internally or externally balanced?

You got lucky on your flywheel diameter. I believe mine is the larger diameter that will need to be turned down. What is your plan to balance your rotational assembly since you have assembled your engine?
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Old March 10th, 2023, 12:56 AM
lizziemeister'sV6 lizziemeister'sV6 is offline
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Default Re: Internally or externally balanced?

Talking about balances - my machine shop guy and I went thru a total of 17 new pistons before he found 6 he would use - he weighed every one and picked the 6 that was the closest. This was on a 351E. I used 379 pistons and had new rods made because the piston pin was higher towards the top of the piston - this increased the rod ratio which was a good thing - the cost of the custom billet rods was the bad thing. Probably would not do that again.
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Old March 10th, 2023, 06:06 AM
Prowbar Prowbar is offline
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Default Re: Internally or externally balanced?

Quote:
Originally Posted by arepoff View Post
You got lucky on your flywheel diameter. I believe mine is the larger diameter that will need to be turned down. What is your plan to balance your rotational assembly since you have assembled your engine?
I'm somewhat thinking I can't get away without a rebalance... I know, this isn't the 'right' way.. These engines have an inbalance due to the configuration already and if you see how much dirt there was in the front pulley and flywheel, it would have added at least 20 grams of external weight.. Yet it ran fine.

The best way would be to re-balance your setup, but the bob weights should be calculated for a V6. Not the typical 50/50 rule that happened to work pretty well on a 90-degree V8.

Have you compared your flywheel to a 305 flywheel? You're certain it is a larger diameter?
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