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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old December 20th, 2013, 03:39 AM
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Default 351 V6 swap to 478 V6

Have a 351C and want to swap to a 478M does anyone know if the 478M will bolt up to my 540 new process transmission
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Old December 20th, 2013, 04:08 PM
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Default Re: 351 V6 swap to 478 V6

Should be problem, that's the transmission I have behind my 432. As long as you have the "big truck" bell housing and larger clutch with the 478 I believe It's a direct swap. That's assuming it's going in a truck, 5500?
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Old December 20th, 2013, 06:33 PM
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Default Re: 351 V6 swap to 478 V6

Opps, that should have read "Shouldn't be a problem" dang spell check
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Old December 20th, 2013, 06:46 PM
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Lightbulb Re: 351 V6 swap to 478 V6

Here's some pic's (hopefully) of mine 14" clutch and truck bell housing
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Old December 20th, 2013, 08:34 PM
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Default Re: 351 V6 swap to 478 V6

5500 GMC:
Do you have the flywheel for the 478? That will be different from the 351. The 478 is externally balanced and the 351 is internally balanced.
regards,
Steve
New Orleans
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Old December 20th, 2013, 10:39 PM
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Default Re: 351 V6 swap to 478 V6

its going in the bus shown in the avatar
my bell-housing has a flat bottom with inspection cover and the starter has two bolts
it also is one piece ,it looks like the bell-housing in the picture is a two piece ?
the motors i am looking at have flywheel and possible bell-housing
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Old December 21st, 2013, 03:45 AM
bigblockv6 bigblockv6 is offline
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Default Re: 351 V6 swap to 478 V6

The flywheel as mentioned in a previous post is really the only issue. You really don't need the bigger bell housing or clutch provided you use a 379 or 432 V6 flywheel which also is externally balanced and has the 8 bolt mating pattern. Definitely a scarce part, I ended up having a custom flywheel built for my 478M conversion.
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Old December 24th, 2013, 08:45 AM
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Default Re: 351 V6 swap to 478 V6

Yeah, I guess I wasn't very clear there. What I should have said was I think life would be easier on you if you use the bigger 478 parts. True, you could keep the smaller 351 bell housing if you really wanted to, but in this application I'm not sure why you would.

Correct me if I'm wrong here... its happened before!

The 5500 series also came with the 401, which used the same bigger truck bell housing as the 478. Unlike putting one in a pickup, room for the bigger bell is not an issue, so you don't have to use the smaller bell housing and hard to find smaller eight bolt 379 flywheel (1973-1974 only) . The 478 had a 13 year run (1962-1974) so these parts shouldn't be as hard to come by, even if they don't come with your replacement engine. Plus, then you have a heavier duty clutch thats made to go with your bigger engine. Seems better/easier all around to me.

Now I'm curious. The 432's I've seen all have the larger flywheel like the 478 and 14" clutch, hadn't heard of them coming with the smaller one like a 379. Did they come both ways? Information on the 379 and especially 432 seems harder to find - I'm always willing to learn!
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Old December 24th, 2013, 06:45 PM
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Default Re: 351 V6 swap to 478 V6

My mistake, you're right the 432 did not use the smaller bell housing that the 379 used. As far as the 5500 series using a 401 what production years are you referring to? I know for a fact that the only gas V6 engines available on 5500 series trucks from 1967-72 were the 305C and 351C, of course that may be diiferent for 1965 and prior years of the BW,LW 5500 series trucks.
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Old December 26th, 2013, 08:43 PM
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Default Re: 351 V6 swap to 478 V6

Well, now I'm not so sure. Maybe I have my wires crossed. Questioning bigblockv6 kinda feels like asking a fish if he's sure he knows how to swim. It sure seems like I've seen the 401 listed in 5500's- maybe in one of Dad's older books then? Was starting to think I may just be crazy, but if so I'm in good company. I checked with the V6 data page on Jolly's site and it lists the 401 (note #8) as "used in the 5500, 6000, & H - 5000 and optional in W & SP -5000." Not sure which years.
The "Motor Truck & Diesel Repair Manual" I have list the Diesel 478 as optionional for conventional model CG 5500 & school bus Model SG 5500- (D478 in 1970 & DH478 in 1971 & 1972). Don't know if that helps you though- not sure which bell housing the Diesel's used. Not trying to muddy the water and I'd hate to give false information. Looks like I need to do more homework here....
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