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Topic: 4 Bolt main?

in Forum: C3 Engines

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4 Bolt main? (1/10)
2/26/13 2:22pm

RedVetteinprogress
Former Member
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West Bend, WI - USA

Vette(s):
1985 silver coupe & 1975 red coupe

Joined: 3/18/2010
Posts: 46

Need a little help here. I am attempting to sell the 350 I pulled out of my 1975 Vette to install a really nice GM crate motor. People ask me if the thing is a 2 or 4 bolt main motor and I have no idea. Short of pulling off the oil pan is there a way to tell? The code on the front of the engine is VO122TXD. Does that help? Also, it's a wimpy L48. What do you guys think? Thanks, Darrell

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Re: 4 Bolt main? (2/10)
2/26/13 2:54pm

Gunslinger
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Frederick, MD - USA

Vette(s):
1969 convertible L71 427/435 4-speed black interior

Joined: 9/8/2003
Posts: 3398

I know to never say never, but an L48 is a 2-bolt engine. That being said, if one uses a 2-bolt block and uses ARP bolts it will withstand prodigious power.

When you get down to it, back then an L48 and L82 used the same block casting...the primary difference was how many holes were drilled for main bearing bolts. The casting numbers should be the same during that time period but the other numbers tell the tale of where the block was cast, what car or truck it was destined for, the horsepower rating and the VIN for the individual vehicle.

Re: 4 Bolt main? (3/10)
2/26/13 7:58pm

Adams' Apple

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 20203

A '75 L48 will almost certainly be a 2 bolt main block. It would be highly unlikely that they had to use a 4 bolt for a shortage of the 2 bolt blocks. It has happened, but prolly not for the '75 era engines.
I agree with Bruce...the two bolt is fine for most applications, unless using a really high compression ratio, nitrous, or forced induction. Many a fine engine has been built using the 2 bolt main casting.
Since you're selling it, of course the 4 bolt will always command more $$$ than the 2 bolt main.

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Re: 4 Bolt main? (4/10)
3/1/13 9:36am

nosal1
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Dunedin, FL - USA

Vette(s):
1980 Corvette Torch Red with Gold metallic 370HP/350 CU.IN.Turbo 350 w/shift kit.Originally CA.Car with 305 CU.IN.

Joined: 3/21/2006
Posts: 262

Good Morning The code from the front tab tells me that you have a 1975-77 Truck motor RPO LS-9 in front of a manual trans. which was engines in 20,30,and CK trucks and were Federal exempt trucks. If you look at the left rear of the block where it bolts to the bell housing or tranny you will see(if cleaned) an embossed GM and numbers.If the 3970010 number is there then it is a good chance it is a 4 bolt block especially when it is used in a truck of those years.In '79 they started 2 bolts in 1/2 ton trucks with the same casting number 3970010. I hope this helps.Have a great day. Sal C

Re: 4 Bolt main? (5/10)
3/1/13 11:08am

73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day. 2023 Accelerate Yellow HTC Stingray

Joined: 7/9/2003
Posts: 908

Aren't most, if not all, 4-bolt engines equipped w/ a forged crank? They usually have a 8" harmonic balancer.

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1973 L-82 4 spd

Re: 4 Bolt main? (6/10)
3/1/13 12:59pm

Hello All, No to the statement that "all 4 bolt have forged cranks,in fact not very many came with forged,albeit there are a list of early engines that had forged starting with the 283 when from '56 to 60-62 the were predominantly forged cranks.Only performance cars i.e.Camaro with 302 some 327's and early 350's. I have all the casting numbers available if anyone would like to peruse them.Most of the 350 and all the 267 and 305 had cast cranks with the last four numbers being 2442,hence not all 4 bolt mains had forged steel cranks. Sorry Sal C

Re: 4 Bolt main? (7/10)
3/1/13 5:56pm

Pretty sure that the LT-1s and L-82s were 4-bolt w/ forged cranks and pickup trucks in at least the early 70s were also. I imagine the Z-28s of that era were also.

Would be interested in any documentation on 4-bolt engines and forged cranks.

BTW, I didn't say "all" 4-bolts came w/ forged cranks.

|UPDATED|3/1/2013 5:56:43 PM (AZT)|/UPDATED|

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1973 L-82 4 spd

Re: 4 Bolt main? (8/10)
3/2/13 4:20am

The LT 1(370 hp) were definitely Steel cranks,however not all L 82 engines were with steel cranks.As mentioned before special edition Camaro's Z-28 with 302 engines and LT 1's used steel cranks. If you would like a listing of all info on identifying Chevy engine parts,send me an email address and I will send the listings,way to much to send here. Have a great day..

Sal C Pacific Performance Motors Florida

Re: 4 Bolt main? (9/10)
3/2/13 6:38am

lukesvette

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HOWELL, NJ - USA

Vette(s):
1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.

Joined: 5/18/2004
Posts: 6812

My 79's original power plant was an L48 and when we pulled the pan, low and behold, it was a victim of 2 bolt main shortages, and I'll be darned if I wasn't staring at 4 bolt man in caps!!

Ya never know...

LukesVette

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Re: 4 Bolt main? (10/10)
3/2/13 10:15am

As I had mentioned in a previous reply,that in '79 cars trucks,Vette's,and Impala's with the GM casting #3970010,had used 2 and 4 bolt mains,hence would not be out of reality if a Corvette of that year would be a 4 bolt main system.They also produced a casting #3970014 that was 4 bolt main for specific vehicles. Again send me PM with your return email address and I will send the casting ID's of all Chevy engines.It is much too large to send in this venue. Have a great day.. Sal C

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