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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old August 28th, 2020, 02:29 AM
Mulana Mulana is offline
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Default Flywheel Modification ???

Question: I purchased a flywheel, exhaust manifolds, flywheel housing and pressure plate assembly off a 351 V6 hoping it would fit my 432. Everything fits except the flywheel. The 351 has a 6 bolt and the 432 has an 8 bolt flywheel mount. Two of the opposing holes fit fine... could I press slugs into 4 of the holes and have 6 new holes machined? Has anyone tried this? Will there be a balance problem?

Thanks-a-bunch.
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Old August 28th, 2020, 08:19 PM
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Default Re: Flywheel Modification ???

Welcome to the Forum Mulana!


Have not heard of too many 432's being used here. Kind of rare I think. Where did you get it?

Anyways here is information from a post by BigblockV6.

Quote:
305,351 & 401 V6 engines are internally balanced so flywheels for these engines are zero balance. Swapping compatible flywheels on these engines isn't an issue provided engines still have the factory balance on them. Engine builders do balance the whole rotating assembly together on just about any engines and if they do add or remove any weight on the flywheel then that flywheel will throw the engine out of balance if it's put on another engine. 379, 432 and 478 V6 engines are externally balanced so there is weight added to the flywheel as well as the front balancer. In my 478M conversion I had a custom flywheel, when the engine was balanced a good amount of weight was welded to the flywheel as well as the front pulley.
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Old August 30th, 2020, 04:28 AM
Mulana Mulana is offline
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Default Re: Flywheel Modification ???

Bigblock V6: Thanks for the quick reply. Your information is exactly what I was looking for. I had hoped the 432 was internally balanced, but I guess not. Onwards and upwards.

I was originally looking for a 478 for my 1-ton pickup, but I couldn't readily find one with the resources I have. I stumbled across the 432 at Anderson Brothers Truck Equipment (used trucks, parts, etc. in Eugene, OR.). This was the biggest GMC V6 they had. They also have three 351's. I scoured through all the parts to find what I needed to complete the 432. I did find a pair of good ToroFlow exhaust manifolds and a pair of 432 manifolds, but one of them is cracked, so I settled with a slightly smaller 351 set of exhaust manifolds.

I did find a 401 with a 5sp. for $1,000 but passed it up. This guy is selling a bunch of GMC body parts/trucks and motors through Craigslist in the Salem, OR. area. He also has a 351 or two.

Thanks-a-bunch, Mx.
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Old August 30th, 2020, 05:07 PM
bigblockv6 bigblockv6 is offline
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Default Re: Flywheel Modification ???

If I were you I would grab that 432, search for a 16 inch diameter 379 flywheel or have one custom made and balance it with the 432's rotating assembly.
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Old August 30th, 2020, 06:19 PM
abus319 abus319 is offline
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Default Re: Flywheel Modification ???

I have an 8 bolt flywheel possibly off of a 401 that I Probably won’t be using.
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Old August 31st, 2020, 02:38 AM
BillT BillT is offline
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Default Re: Flywheel Modification ???

You can even see that it is Externally Balanced.

Nice.

Date Code looks like August 1, 1967.
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-'71 GMC 9500 Flatbed Dump, 637 V-8

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Old August 31st, 2020, 08:11 PM
Mulana Mulana is offline
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Default Re: Flywheel Modification ???

Quote:
Originally Posted by abus319 View Post
I have an 8 bolt flywheel possibly off of a 401 that I Probably won’t be using.
I have a handle on a 401 flywheel at the moment. If it doesn't work out, I'll let you know.

Thanks-a-bunch.
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Old September 16th, 2020, 03:42 AM
Mulana Mulana is offline
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Default Re: Flywheel Modification ???

Hey, everybody.... thanks for your help. I purchased a 401 flywheel from one of the subscribers, and I will get it balanced for my 432.

Thanks again, Mx.
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