What is meant by 4-bolt mains?

What is meant by 4-bolt mains?
There are 4 bolts that bolt down the 2, 3, 4 main caps on a SBC
http://www.finitesite.com/markwallas/mains.jpg

Understood thankyou very much! 4 bolt mains = good!

2 bolt converted to 4 bolt and splayed=BETTER than regular 4 bolt!

And to expand on that, 2-bolt w/ main-studs in place of stock type bolts works well too for a cheaper, stronger deal.

More info, the 400 SB's outer bolts punch through the main bearing webs so are a tad weaker than the 2-bolt 400 blocks. That's why it would be better to use a 2-bolt 400 SB block and install splayed-maincaps like already mentioned by Berry b/c the outer bolts tie into the pan rails better for more strength.

pdq67

And to expand on that, 2-bolt w/ main-studs in place of stock type bolts works well too for a cheaper, stronger deal.

More info, the 400 SB's outer bolts punch through the main bearing webs so are a tad weaker than the 2-bolt 400 blocks. That's why it would be better to use a 2-bolt 400 SB block and install splayed-maincaps like already mentioned by Berry b/c the outer bolts tie into the pan rails better for more strength.

pdq67

Studs don't make the caps and stronger as its still a grey cast cap with better hardware same as putting a new set of rod bolts in a set of rods it doesn't make the rods any stronger it just better hardware.

Right, the stronger the fastener, the more clamping force it can withstand, the harder it is to move the parts apart so therefore stronger the assembly, imho!!

pdq67

PS., and you can't create a crack in compression!!

Right, the stronger the fastener, the more clamping force it can withstand, the harder it is to move the parts apart so therefore stronger the assembly, imho!!

pdq67

PS., and you can't create a crack in compression!!

It still does not change the material of the caps as they are a gey cast cap in a very narrow register unlike the 2 bolt 400 block the caps are a lot wider to handle the extra side load from the extra stroke or even a BBC has wide registers to accomadate more stroke and torque.

After 36 years of seeing 2 bolt main blocks with there registers fretted from the caps moving around and we have seen that happen with studs or bolts so studs from what we have seen does not really solve anything. If its under 350 horse a 2 bolt will work fine any more then that then we start to seeing problems with caps moving or uneven wear on the main bearings as it not to hard to see whats going on.

Here is an interesting link to look over http://ls1tech.com/forums/showthread.php?t=652566

Carl,

I torqued my 2-stud 496 BB to 130 pounds so I am not worried about cap fretting like the pic's show b/c I'm not going to rpm her!

But you are right!!

pdq67

Carl,

I torqued my 2-stud 496 BB to 130 pounds so I am not worried about cap fretting like the pic's show b/c I'm not going to rpm her!

But you are right!!

pdq67

BBC have a wide register and you don't the fretting like you would see on a 350 2 bolt block and the 2 bolt BBC's we build for high performance use we also use studs on and line hone the block as well.

Am not quite clear on the numbers above by Carl.

Im sure the space across the main bearings for the point where the caps fit is the same on the 350 small blocks and the 400s. The caps are slightly thicker measured from the front to the back by about .035". The 400 caps are stronger by design. They are also slightly thicker where the shells sit from the top to the bottom at the center. This is on the 2 bolt main blocks, I don't have a 4 bolt mian here today

The studs are necessary on all the small blocks because of the thread sizes. They will the the caps from cahttering more than the factory bolts like pdq says!

Harry P.Hunter

Am not quite clear on the numbers above by Carl.

Im sure the space across the main bearings for the point where the caps fit is the same on the 350 small blocks and the 400s. The caps are slightly thicker measured from the front to the back by about .035". The 400 caps are stronger by design. They are also slightly thicker where the shells sit from the top to the bottom at the center. This is on the 2 bolt main blocks, I don't have a 4 bolt mian here today

The studs are necessary on all the small blocks because of the thread sizes. They will the the caps from cahttering more than the factory bolts like pdq says!

Harry P.Hunter


A 2 bolt 400 cap is far wider then a 350 2 bolt cap and using studs may help on the clamping force but we still see studed 2 bolt caps walk around due to the caps are stock caps and they do flex wether you are using studs or bolts on a 350 2 bolt cap block

We deal with about 200 blocks a year and we see a lot of guys having problems with over powering 2 bolt caps WITH studs or bolts and we get calls and emails about this all the time so we don't just base our info on one or two blocks that guys have run for years.

Hi carl I can't be sure now but I think the caps and register sizes are the same on the small block 2 bolt main engines. I'm pretty certain about that but I will measure one tromorrow.

I remember the bolts being separated further apart but where the caps rest is the same. Not a big deal anyway, thanks.

Harry P.Hunter