Big Block help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Patch** · 05-19-2021, 01:54 PM

I'm looking at a 454 engine today. 12550313 casting number. 4 bolt main engine WITH the mechanical fuel pump boss machined into it and it has a pump on it now. 6 bolt aluminum timing cover and 1 piece rear main seal. If I did my investigating correctly, this should be a Gen VI...yes? Any input would be greatly appreciated....Patch

geezer#99 · 05-19-2021, 02:02 PM

According to mortec it could be a gen 5 too.

https://www.mortec.com/bbc.htm

**Patch** · 05-19-2021, 02:05 PM

With the 6 bolt cover I believe that designates it a 6...but that's what I'm trying to verify. I've also read that Gen V's did not have the mech fuel pump boss machined or even present....so much too learn...lol. Thanks...

b454rat · 05-19-2021, 06:51 PM

Could be a crate motor...

**AussieinNC** · 05-20-2021, 04:29 PM

Details for 12550313

Manufacturer Chevrolet
Category Engine Blocks
Type Big Block V8
Date 1991+
Notes 454, 4 bolt, Generation V crate motor,
Generation VI 4.25 bare block, fuel pump boss

More info if you are interested...

No Gen 5 has a fuel pump boss. Gen 6 crate and service blocks do.
Gen 5 timing covers LOOK like MK IV but are different at the pan seal.
Gen 6 timing covers only have 6 bolts. Gen 5 and MK IV have 10,
The lifter bores on the Gen 6 are approx. .300 taller than MKs and Gen 5.

Be very careful if you are considering a flat tappet mechanical cam for a Gen VI ...lots of areas where it can go very wrong...hyd roller is the way to go IMHO

**Patch** · 05-23-2021, 06:22 PM

Got it apart yesterday. Definitely a Gen VI replacement block. Still has crosshatch in the cylinders. Could be fun to rebuild it as a roller! Interesting that the guide plates are marked Mark V. The stamp on the back of the block I don't know what it means either.

05-19-2021, 01:54 PM	#1
Patch Senior Member Join Date: Jul 2002 Location: Oak Harbor, WA Posts: 703	Big Block help I'm looking at a 454 engine today. 12550313 casting number. 4 bolt main engine WITH the mechanical fuel pump boss machined into it and it has a pump on it now. 6 bolt aluminum timing cover and 1 piece rear main seal. If I did my investigating correctly, this should be a Gen VI...yes? Any input would be greatly appreciated....Patch __________________ Patch

05-19-2021, 02:02 PM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,512	Re: Big Block help According to mortec it could be a gen 5 too. https://www.mortec.com/bbc.htm

05-19-2021, 02:05 PM	#3
Patch Senior Member Join Date: Jul 2002 Location: Oak Harbor, WA Posts: 703	Re: Big Block help With the 6 bolt cover I believe that designates it a 6...but that's what I'm trying to verify. I've also read that Gen V's did not have the mech fuel pump boss machined or even present....so much too learn...lol. Thanks... __________________ Patch

05-19-2021, 06:51 PM	#4
b454rat Senior Member Join Date: May 2004 Location: Binghamton, NY Posts: 3,453	Re: Big Block help Could be a crate motor...

05-20-2021, 04:29 PM	#5
AussieinNC Moderator Join Date: Jun 2017 Location: Cherryville, NC Posts: 2,154	Re: Big Block help Details for 12550313 Manufacturer Chevrolet Category Engine Blocks Type Big Block V8 Date 1991+ Notes 454, 4 bolt, Generation V crate motor, Generation VI 4.25 bare block, fuel pump boss More info if you are interested... No Gen 5 has a fuel pump boss. Gen 6 crate and service blocks do. Gen 5 timing covers LOOK like MK IV but are different at the pan seal. Gen 6 timing covers only have 6 bolts. Gen 5 and MK IV have 10, The lifter bores on the Gen 6 are approx. .300 taller than MKs and Gen 5. Be very careful if you are considering a flat tappet mechanical cam for a Gen VI ...lots of areas where it can go very wrong...hyd roller is the way to go IMHO __________________ Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox Last edited by AussieinNC; 05-20-2021 at 04:39 PM.

05-23-2021, 06:22 PM	#6
Patch Senior Member Join Date: Jul 2002 Location: Oak Harbor, WA Posts: 703	Re: Big Block help Got it apart yesterday. Definitely a Gen VI replacement block. Still has crosshatch in the cylinders. Could be fun to rebuild it as a roller! Interesting that the guide plates are marked Mark V. The stamp on the back of the block I don't know what it means either. Attached Images __________________ Patch



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