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Old 12-30-2011, 07:22 PM   #1
davepl
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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"?
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Old 12-30-2011, 11:30 PM   #2
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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
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Old 12-31-2011, 08:32 AM   #3
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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.
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Old 12-31-2011, 03:32 PM   #4
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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.
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Old 12-31-2011, 03:39 PM   #5
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Re: Are big block trucks 2-bolt or 4-bolt mains?

If you really need to know, drop the oil pan.
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Old 12-31-2011, 03:51 PM   #6
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Re: Are big block trucks 2-bolt or 4-bolt mains?

You might be able to see through the oil plug hole with a flashlight.
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Old 12-31-2011, 07:22 PM   #7
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Re: Are big block trucks 2-bolt or 4-bolt mains?

Why is it really all that important?
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Old 12-31-2011, 10:42 PM   #8
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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
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Old 12-31-2011, 10:45 PM   #9
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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
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Old 01-01-2012, 02:42 AM   #10
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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!
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Old 01-01-2012, 03:00 AM   #11
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Re: Are big block trucks 2-bolt or 4-bolt mains?

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Originally Posted by prostreetC-10 View Post
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.
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Old 01-01-2012, 11:40 AM   #12
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Re: Are big block trucks 2-bolt or 4-bolt mains?

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But lets not forget that 4-bolts are weaker.
What? How?
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Old 01-01-2012, 11:54 AM   #13
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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...
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Old 01-01-2012, 10:58 PM   #14
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Re: Are big block trucks 2-bolt or 4-bolt mains?

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Originally Posted by 1972RedNeck View Post
What? How?
Quote:
Originally Posted by mightymouse View Post
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.
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Old 01-01-2012, 11:27 PM   #15
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Re: Are big block trucks 2-bolt or 4-bolt mains?

Quote:
Originally Posted by Livrat View Post
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
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Old 01-01-2012, 11:40 PM   #16
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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.
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Old 01-01-2012, 11:52 PM   #17
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Re: Are big block trucks 2-bolt or 4-bolt mains?

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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!
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Old 01-02-2012, 12:13 AM   #18
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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.
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Old 01-02-2012, 07:46 AM   #19
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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)...
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Old 01-02-2012, 08:15 AM   #20
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Re: Are big block trucks 2-bolt or 4-bolt mains?

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Originally Posted by ProStreet68SB View Post
This. Except you have 2 bolt bolt block machined for splayed 4 bolt mains.
x2.
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Old 01-03-2012, 10:37 PM   #21
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Re: Are big block trucks 2-bolt or 4-bolt mains?

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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.
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