Two/Four-bolt Blocks

[Stallion]

I was just reading my book, and Newton talks about two bolt and four bolt blocks and that four bolt were more necessary for racing, etc. Two bolt, he said, were for normal street use.

But, what does he mean with these bolt indications? Where are these bolts, and what are they for (of course, I guess for applying to attach parts?) where these numbers come from?

Can somebody explain to me the significance of this "option"? Thanks!

TR

 

[Eric]

Stallion,

Here's the description I found in the Corvette Glossary.

2-Bolt, 4-Bolt Mains
The number of bolts holding the main journal caps on. The 4 bolt main is stronger than the 2 bolt main and so is more desirable to racers. However, all small journal engines were only 2 bolt mains and survived many racing series. The need for 4 bolt mains on the street is greatly exaggerated except for heavy load towing.

 

[Stallion]

Thanks, Eric! From now on, I'll check the glossary before posting. But, I have a question of that definition (one which wasn't in the glossary ): "main journal caps". What are these? What part of the blocks are they? Thanks!

And, sorry about the wrong forum posting.

Thanks again, Eric!

TR

 

[Ken]

The reference to how many bolts the crank has, comes from the fact that the main bearing caps are different for differing applications. Race applications where the engine will routinely see the rpms get into the seven-thousand revolutions per minute, the main caps should be fastened to the block with four bolts, preferably with the outer two "splayed" at an angle to the middle two. Engines the seldom see rpms in the high-six-thousand revolutions per minute range such as one in a daily street-driven vehicle require no more than two bolt main caps.

Regular production 350s that will see high rpms should have splayed four-bolt main caps. The 400ci small block from the truck is another story, it's a little beefier...

This excerpt came from Chevy High Performance magazine's Performance Q&A by Kevin McClelland

The 400 small-blocks are a different animal. They have larger main journals (2.65 versus 2.45 inches), and the main caps are the same width in both the four-bolts and two-bolts. The important things here are a good align-hone job and quality fasteners. (Note: I have both.) The difference between the two- and four-bolts is in the main webs of the block. The two-bolt blocks actually have a stronger main web area than the four-bolts do. If you plan to build a nasty 400, start with a two-bolt block and install aftermarket splayed four-bolt caps. A properly prepared two-bolt block will hold up to 500 hp.

Hope this helps you some.

 

[Eric]

Thanks, Eric! From now on, I'll check the glossary before posting. But, I have a question of that definition (one which wasn't in the glossary ): "main journal caps". What are these? What part of the blocks are they? Thanks!
And, sorry about the wrong forum posting.
Thanks again, Eric!

TR

Hey no problem and you didn't post in the wrong forum necessarily since the questions do apply to C3s but I thought they fit better in general tech since it applies to all cars.

I think I have an exploded cross section of a SBC (small block chevy) somewhere around here. I'm on my way to bed now but I'll try to dig it up tomorrow and scan it for you.

- Eric

 

[Stallion]

>> I thing I have an esploded cross section of a SBC (small block chevy) somewhere around here. I'm on my way to bed now but I'll try to dig it up tomorrow and scan it for you. <<

Thanks, Eric! I appreciate it.

And yes, Ken, your description has helped me. But, just another quick question. The bolts (whether two or four) are on the "main bearing caps" as you say, but what do these caps cap? I think I remember reading about some sort of caps on the block, but I'm not sure and it doesn't seem to be fitting in place. Would these caps have anything to do with sealing off pistons or maybe above the valves?

Thanks again!

TR

 

[Ken]

What you need is...

...A VISIBLE V-8!! :J



Compare prices and read reviews on the Visible V-8 here.

_ken :J

 

[vigman]

Caps Cranks & Bearings .....Oh my!

Here's the deal,( simple version )

The crank needs a bearing to support the loads.. in the case of a small block Chevy there are 5 bearings to support the entire length of the crank.

The block is manufactured in such a fashion that it is only 1/2 of the diameter of the crank journal is supported in the actual block.. the other half is the bearing caps... the bearing caps mount into the block via bolts.... the discussion then happens whether you need 2 ( bolts ) or 4 to hold the bearing caps on to the block.

As far as the actual bearings go.. the bearing surface is a flat piece of composite metal with oil channels in an U shape... this bit sits inside of the bearing cap, there is a mirror of this bearing in the block itself.. So the sandwich goes ( from top to bottom)

Top of block
bearing(Top half)
crank
bearing (Bottom half)
Bearing cap

and the bearings actually aren't, it's the oil film that the crank rides on
( when everything is kosher)

So the more ponies you generate...( 400+) the bigger bearing cap SUPPORT you need to keep the crank from BLOWING out the bottom of the block.

A 375hp motor will run for YEARS in a 2 bolt configuration.

So yeah.. 4 bolt is better IF you race PROFESSIONALLY

Or operate a tow truck or other heavy hauler.


Vig!

 

[Ken]

A properly prepared two-bolt block will hold up to 500 hp.

 

[Stallion]

I understand now, thanks a lot!

But, why aren't all blocks just a default of 4 bolts? After all, it's not that much more hardware, but you might as well take the extra step, right? So in other words, why wouldn't you want to just have a four bolter? You know, better to be safe than sorry.

TR

 

[Stallion]

And also, when I'm going to look at Vettes, where would I look to see if it's two or four bolt block? Any way easily accessed, or should I just take his word for it? Or, should it not really matter which is when I go to buy a Vette?

Thanks again!

TR

 

[Ken]

You know, I hope you guys don't think that I was joking when I mentioned the "Visible V-8" engine; it's a great learning tool!

_ken