Are big block trucks 2-bolt or 4-bolt mains? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

davepl · 12-30-2011, 07:22 PM

My 1970 has the L-47 402, which I assume is pretty close to the Impala/Camaro 396/325.

I'm wondering if trucks got 4-bolt mains... I couldn't find any specs on the L-47 (if someone knows, please point me at them!).

Or is it a case of "some were, some weren't"?

1968SWBBigBlock · 12-30-2011, 11:30 PM

According to my books they could have been 2 or 4 bolts in the trucks
It really is not that important in the big skeem on things

**special-K** · 12-31-2011, 08:32 AM

Get your casting numbers off the front of the block and look it up on www.nastyz28.com . BTW,all '70s were 402s,even SS396s.

davepl · 12-31-2011, 03:32 PM

I did look it up on nastyz28, but it just said "L-47 402 310hp". Is there some other resource on that site that breaks it down by 2-bolt vs 4-bolt? I couldn't find one.

**too much stuff** · 12-31-2011, 03:39 PM

If you really need to know, drop the oil pan.

1972RedNeck · 12-31-2011, 03:51 PM

You might be able to see through the oil plug hole with a flashlight.

ProStreet68SB · 12-31-2011, 07:22 PM

Why is it really all that important?

71 super · 12-31-2011, 10:42 PM

It is more than likely a two bolt. the one in my 71 is a 2 bolt. Heck it does not matter these things in stock form dont turn enough rpm to worry nor do they need to. Drive it and enjoy the bb

Livrat · 12-31-2011, 10:45 PM

I do believe there were no 4 bolt 396's or 402's in our trucks, from the factory the only 4 bolts were the 375hp/396, 425hp/396's and higher hp 427's.
I have been lead to believe from personal experience, (I have owned and built many a big block in the last 30 years):
One way to tell is look above the oil filter boss.. all the early 4 bolt blocks were drilled and tapped for an external oil cooler, if the block has two pipe plugs (one 1/2" and one 1/4') its a 4 bolt. the 2 bolts only had a single 1/4' threaded boss, (its where your oil pressure gauge line is attached).

prostreetC-10 · 01-01-2012, 02:42 AM

I have played the 2 bolt/4 bolt lottery so many times and have never came up with a 4 bolt. A 2 bolt with a steel crank is good for about 600 HP. One place to find 4 bolts is in motorhomes!

ProStreet68SB · 01-01-2012, 03:00 AM

Quote:

Originally Posted by prostreetC-10

I have played the 2 bolt/4 bolt lottery so many times and have never came up with a 4 bolt. A 2 bolt with a steel crank is good for about 600 HP. One place to find 4 bolts is in motorhomes!

I'll be at 800hp on a stock 2bolt block.

But lets not forget that 4-bolts are weaker.

1972RedNeck · 01-01-2012, 11:40 AM

Quote:

Originally Posted by ProStreet68SB

But lets not forget that 4-bolts are weaker.

What? How?

mightymouse · 01-01-2012, 11:54 AM

if its like a small block i always heard a 2-bolt is stronger. cause the main webbing is thicker than a 4-bolt . Ive heard the best thing to do is have 2-bolt block machined for 4-bolt main caps. looking at it makes sense.but i'm no motor man just things Ive been told...

ProStreet68SB · 01-01-2012, 10:58 PM

Quote:

Originally Posted by 1972RedNeck

What? How?

Quote:

Originally Posted by mightymouse

if its like a small block i always heard a 2-bolt is stronger. cause the main webbing is thicker than a 4-bolt . Ive heard the best thing to do is have 2-bolt block machined for 4-bolt main caps. looking at it makes sense.but i'm no motor man just things Ive been told...

This. Except you have 2 bolt bolt block machined for splayed 4 bolt mains.

gearys 5600 · 01-01-2012, 11:27 PM

Quote:

Originally Posted by Livrat

I do believe there were no 4 bolt 396's or 402's in our trucks, from the factory the only 4 bolts were the 375hp/396, 425hp/396's and higher hp 427's.
I have been lead to believe from personal experience, (I have owned and built many a big block in the last 30 years):
One way to tell is look above the oil filter boss.. all the early 4 bolt blocks were drilled and tapped for an external oil cooler, if the block has two pipe plugs (one 1/2" and one 1/4') its a 4 bolt. the 2 bolts only had a single 1/4' threaded boss, (its where your oil pressure gauge line is attached).

This x2^^^ The only 4-bolts that I personally have seen are L-78 375hp 396,Ls-6 and Ls7 454's, and the high horse 427's

indianbullet · 01-01-2012, 11:40 PM

If you find a big block look at the pipe plug above the oil filter. If it has a huge plug 1" pipe rather than the 3/4" pipe plug it will be a 4-bolt. At least this has held true on all the blocks built before the early 80's when I was in the machine shop.
As for small blocks back in the day. I've seen many a case of beer lost by those that thought they could pin point one via casting #'s etc. gotta pull the pan.

Livrat · 01-01-2012, 11:52 PM

Quote:

Originally Posted by indianbullet

If you find a big block look at the pipe plug above the oil filter. If it has a huge plug 1" pipe rather than the 3/4" pipe plug it will be a 4-bolt. At least this has held true on all the blocks built before the early 80's when I was in the machine shop.
As for small blocks back in the day. I've seen many a case of beer lost by those that thought they could pin point one via casting #'s etc. gotta pull the pan.

I stand corrected... it is a 1" pipe plug above the oil filter and not a 1/2" like I posted above, Indianbullet thanks for the clarification!

mcbassin · 01-02-2012, 12:13 AM

I pulled my pan to change the gasket back in the 80s only to be disappointed to see it was a 2 bolt. At the time I remember thinking someone put a car motor in my truck. I thought all truck big blocks were 4 bolts then. That was before I knew it really didn't make any difference.

bobs409 · 01-02-2012, 07:46 AM

Got a question then... My 69 wrecker has it's original 350 and it has 4 bolt mains. (I think I heard all the 350's in these trucks were 4 bolt but not sure)

Why would they use a 4 bolt in a small block and not the big block?

I can see why it's not important for a stock built engine so why did any of them have it? (just wondering & for conversation purposes)...

GRX · 01-02-2012, 08:15 AM

Quote:

Originally Posted by ProStreet68SB

This. Except you have 2 bolt bolt block machined for splayed 4 bolt mains.

x2.

indianbullet · 01-03-2012, 10:37 PM

Quote:

Originally Posted by bobs409

Got a question then... My 69 wrecker has it's original 350 and it has 4 bolt mains. (I think I heard all the 350's in these trucks were 4 bolt but not sure)

Why would they use a 4 bolt in a small block and not the big block?

I can see why it's not important for a stock built engine so why did any of them have it? (just wondering & for conversation purposes)...

Every stock 350 I have pulled out of these truck has been of the nodular Iron
4-bolt main cap variety. Very desirable blocks as the years progressed the blocks went to cast iron 4-bolt caps. Not as strong as the nodular iron caps.

12-30-2011, 07:22 PM	#1
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Are big block trucks 2-bolt or 4-bolt mains? My 1970 has the L-47 402, which I assume is pretty close to the Impala/Camaro 396/325. I'm wondering if trucks got 4-bolt mains... I couldn't find any specs on the L-47 (if someone knows, please point me at them!). Or is it a case of "some were, some weren't"? __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

12-30-2011, 11:30 PM	#2
1968SWBBigBlock Active Member Join Date: Oct 2006 Location: Ohio Posts: 1,643	Re: Are big block trucks 2-bolt or 4-bolt mains? According to my books they could have been 2 or 4 bolts in the trucks It really is not that important in the big skeem on things __________________ 1968 SWB 454 + .040, 490HP x 540 FT pounds of Torque 10-1 Kb Forged pistons, recon rods w/ ARP wave loc bolts 781 heads Ported with 2.19/1.88 SSTvalves Lunati 60204 cam, Micro Trol lifters, Ported Edelbrock Performer Rpm manifold armor coated, Pertronix Triple Strike Ignition Holley 770 Street Avenger carb,Headers armor coated Built by Watson Ruppel Performance in Sarahsville Ohio. Hardshift Tranny Built Turbo 350,TSI 10" 3000 stall 12 Bolt Eaton Posi 4.10 Richmond Gears moser axles 18.5" x 31" Hoosier Pro Street Radials ET Classic 5 Wheels - polished Power Steering, Power Brakes,Disc Brakes,Tach & Gauge Dash, Tilt,Factory Air (gone) Custom Paint & Body Work Special thanks to my wife, my son and my money tree

12-31-2011, 08:32 AM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Are big block trucks 2-bolt or 4-bolt mains? Get your casting numbers off the front of the block and look it up on www.nastyz28.com . BTW,all '70s were 402s,even SS396s. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

12-31-2011, 03:32 PM	#4
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Are big block trucks 2-bolt or 4-bolt mains? I did look it up on nastyz28, but it just said "L-47 402 310hp". Is there some other resource on that site that breaks it down by 2-bolt vs 4-bolt? I couldn't find one. __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

12-31-2011, 03:39 PM	#5
too much stuff Roadtrip! Join Date: Feb 2003 Location: Grand Rapids MN Posts: 13,786	Re: Are big block trucks 2-bolt or 4-bolt mains? If you really need to know, drop the oil pan. __________________ 67 gmc custom lwb dakota truck. Sold...And bought back 69 swb 4x4 project (in progress) 70 c-10 lwb texas truck 70 4x4/BB/bkts/posi/tach(retired) 70 swb (wifes) 70 jimmy camper 71 K-5 factory 2wd 71 cheyenne 4x4/tach/posi/ plow rig 71 Cheyenne20 BB, buckets, tach, tilt, 4 speed 72 jimmy CST wyoming rig 72 jimmy Colorado rig 72 lifted texas 4x4 3/4 ton burb 65 fury conv. 383/auto 65 chrysler 300 "L" 413 auto

12-31-2011, 07:22 PM	#7
ProStreet68SB The Engine Whisperer Join Date: Sep 2006 Location: Ohio Posts: 770	Re: Are big block trucks 2-bolt or 4-bolt mains? Why is it really all that important?

12-31-2011, 10:42 PM	#8
71 super Registered User Join Date: Sep 2005 Location: Canton North carolina Posts: 3,080	Re: Are big block trucks 2-bolt or 4-bolt mains? It is more than likely a two bolt. the one in my 71 is a 2 bolt. Heck it does not matter these things in stock form dont turn enough rpm to worry nor do they need to. Drive it and enjoy the bb __________________ 67 blue step side- bb 68 gold and white swb cst anniversary 68 custom swb hot rod Ls swap 69 swb cst 6 cylinder/ overdrive 69 black/black cst bb swb 70 orange and white cst Canada built truck swb bb 71 black and white super swb bb 71 red and white super swb 72 green and white super swb 4x4 62 nova wagon 400 series Ls swapped 68 Camaro 327/4 speed- 1 owner, original paint 66 Volkswagen bettle 69 auto stick Volkswagen Beetle

12-31-2011, 10:45 PM	#9
Livrat Member #1049 Join Date: Jun 2000 Location: Troy Montana Posts: 3,940	Re: Are big block trucks 2-bolt or 4-bolt mains? I do believe there were no 4 bolt 396's or 402's in our trucks, from the factory the only 4 bolts were the 375hp/396, 425hp/396's and higher hp 427's. I have been lead to believe from personal experience, (I have owned and built many a big block in the last 30 years): One way to tell is look above the oil filter boss.. all the early 4 bolt blocks were drilled and tapped for an external oil cooler, if the block has two pipe plugs (one 1/2" and one 1/4') its a 4 bolt. the 2 bolts only had a single 1/4' threaded boss, (its where your oil pressure gauge line is attached). Last edited by Livrat; 12-31-2011 at 10:45 PM. Reason: spelling

01-01-2012, 02:42 AM	#10
prostreetC-10 My Carbon Footprint Join Date: Oct 2008 Location: Orygun Posts: 5,527	Re: Are big block trucks 2-bolt or 4-bolt mains? I have played the 2 bolt/4 bolt lottery so many times and have never came up with a 4 bolt. A 2 bolt with a steel crank is good for about 600 HP. One place to find 4 bolts is in motorhomes! __________________ A quick "pedalfest" *Still getting loose (carb test)* 496 Initial fire up video!

01-01-2012, 11:54 AM	#13
mightymouse Registered User Join Date: Feb 2011 Location: Crowley TX Posts: 979	Re: Are big block trucks 2-bolt or 4-bolt mains? if its like a small block i always heard a 2-bolt is stronger. cause the main webbing is thicker than a 4-bolt . Ive heard the best thing to do is have 2-bolt block machined for 4-bolt main caps. looking at it makes sense.but i'm no motor man just things Ive been told...

01-01-2012, 11:40 PM	#16
indianbullet Registered User Join Date: Aug 2011 Location: North Cal and no Sac or Bay area is not NORTH Posts: 31	Re: Are big block trucks 2-bolt or 4-bolt mains? If you find a big block look at the pipe plug above the oil filter. If it has a huge plug 1" pipe rather than the 3/4" pipe plug it will be a 4-bolt. At least this has held true on all the blocks built before the early 80's when I was in the machine shop. As for small blocks back in the day. I've seen many a case of beer lost by those that thought they could pin point one via casting #'s etc. gotta pull the pan. __________________ Never argue with an idiot, they will bring you to their level and beat you with experience..

01-02-2012, 12:13 AM	#18
mcbassin Still Learning Join Date: Jul 2009 Location: Central Oklahoma Posts: 10,108	Re: Are big block trucks 2-bolt or 4-bolt mains? I pulled my pan to change the gasket back in the 80s only to be disappointed to see it was a 2 bolt. At the time I remember thinking someone put a car motor in my truck. I thought all truck big blocks were 4 bolts then. That was before I knew it really didn't make any difference. __________________ Mike "69 Short Wide" My Project 86 Silverado Landen's Project Instagram: @mcbassin My Website C/10 Club Oklahoma Facebook Group

01-02-2012, 07:46 AM	#19
bobs409 1969 Custom 30 wrecker Join Date: Sep 2001 Location: Pottsville, Pa Posts: 2,611	Re: Are big block trucks 2-bolt or 4-bolt mains? Got a question then... My 69 wrecker has it's original 350 and it has 4 bolt mains. (I think I heard all the 350's in these trucks were 4 bolt but not sure) Why would they use a 4 bolt in a small block and not the big block? I can see why it's not important for a stock built engine so why did any of them have it? (just wondering & for conversation purposes)... __________________ Bob 63 Impala 283/PG/3.36 (under restoration) 66 Impala 327/PG/3.36 66 Chevelle SS 409/M22/3.55 69 Chevelle 307/PG/3.08 (future restoration) 69 C10 short stepside 454/TH350/3.73 69 Custom 30 tow truck 350/4 spd/4.10 (resto done, CRUISIN TIME!) 71 Cheyenne 20 fleetside 350/4 spd/4.10 71 Chevelle 6/PG/3.08 72 Chevelle 454/M21/4.10



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