4 bolt mains

Quick survey who has had 2 bolt block fail.

 

I haven't. But I'm interested in this one. Seems like from what I hear the 2 bolt main blocks do fine for street application, RPM's up to about 6k.

 

A friend had one fail....but we think the overdose of nitrous by the previous owner was responsible.

 

I've run them in stock cars up to 7000 RPMs with no problems. In a claimer class, the 4-bolt main blocks were out of the question $$ wise.

Bob

 

I blew my 327, but the mains didn't fail...

 

This is kind of a half-assed question. Are we talking Ford, Chevy, MoPar, other? Some of it matters.

A 2 bolt 509 Chevy 400 block is stronger as a 2 bolt than its 400 4 bolt brother. If a 509 400 block is drilled for 4 bolt it will become weaker and will not hold up as well as if it were left alone.

So it does matter on the manufacturer as well as the block and its application.

 

Next time you go too a scrap yard, ask for a 350 4-bbl motor out of a '70 (if possible) chevy/GMC pickup... I lucked out a few times with 4-bolt blocks with a "steel" crank...
For only 100 bucks...

 

im pretty sure you can blow up any engine with enough beating.

 

I have blown up 2 bolt engines. And I have run two bolt 468 inch engines for several years at El Mirage and Bonneville with no failures. The engines that failed didn't have anything to do with main studs.

 

^ ^ ^ Words to live by! ^ ^ ^

 

2 bolt what block? Some only come in 2 bolt configuration.

I have seen 2 bolt GM blocks fail but only under extreme use.

 

Ive had a 4 400 sbc 4 bolts and they all had cracks in the main webs when taken apart.Theres more too it than the 4 bolt 2 bolt thing,I think having a 2 bolt 350 with studs and factory nodular caps is better than a 4 bolt with standard grey cast caps.Nodular caps are more important imho.I make sure to use nodular caps on every chevy in my fleet seen too many cast caps break in the center..

 

If a 509 400 block is drilled for 4 bolt it will become weaker and will not hold up as well as if it were left alone.

If drilled for a factory style 4 bolt cap, that's true due to the extra material taken out of the web area of the block. If drilled for a 4 bolt cap with splayed outter bolts, some strength can be gained.

 

According to what I've seen on Craigslist,aren't they all 4 bolt mains?

 

2 bolt what GM blocks?

I have never personally seen a 2 bolt Chevrolet engine fail from main cap failure. And often wondered why we get excited about a 4 bolt block.

~Alden

 

I have had two four bolt main Chevy small blocks break the caps in two on the center mains, but never on a two bolt.

 

18 psi and just a drop or two nitric acid for good measure. Pretty sure that the main caps let loose before the forged crank busted but how would you know.
Did I mention extreme?

For the average street engine a 2 bolt block will hold up just fine, but when you start throwing the meat to anything you need to help it all that you can.

 

Sometimes $100 was a budget-buster and most of our engines came right out of junk cars that ran good and were doctored up from there.

I had one 350... just swapped in the solid cam, intake manifold, carb, distributor and went a runnin'... good enough for a top 10 finish all the time and a top 5 now and then. Those I'd run at a conservative 6300 RPMs.

Bob

 

And out of a Vette

 

If used as intended there are very few engines with 2 bolt mains that have main cap problems. Generally speaking, a lot of people who think they need a 4 bolt block really don't. Depending on the engine, at some point increased RPMs, a large large power increase, or in some cases heavy use like truck or boat, can make better caps and fastening necessary.

The caps on early SB Chevy engines were known to move around when the engine was modified a little. The 472/500 Cadillac is fine in normal use, but the stock caps will move around if RPMs are increased too far. The Buick/Olds/Pontiac/Rover aluminum V-8 tended to have problems with the caps moving around on the block. Those engines eventually got 4 bold mains.

 

Aren't they all!

 

4-bold mains????.. I guess they could be if they were BiG enough..

 

We ran 265 two bolt main engines in our Gasser. would shift at 8500 never had a problem, but we ran studs rather than the factory style bolts

 

I recently rebuilt a motor using a low milage motor out of a 1981 Corvette. It had low compression heads and produced very low horse power numbers, something in the neighborhood of 185hp. And it wasn't the fabled four bolt main motor everyone desires. I replaced the heads, cam shaft, intake, pistons, etc, etc with newer, better components and ended up with a very strong, smooth running engine. And the missing main cap bolts don't seem to be hurting it's performance any.

 

Odd bearing wear patterns that indicated either the block or crank twisting longitudinally as well as loss of main cap register in a 650hp BB. I would say failure was pending...

 

Sorry to shatter your perception that I am perfect, but I'm not sure that my typo makes much difference in whether one needs a 4 bolt block. Nearly all my typing is done with only two fingers. Considering that I'm pretty fast, but obviously fat finger typing is possible even with just two fingers.

 

..... and fretting on the mounting faces indicates cap movement on the block.

 

hell I got skinny fingers and still screw it up.

Well I got to zoom to the nursing home, one of my favorite things to do and I want to say something out of oure meaness:

A long time ago I was in the Ol' man's shop using his late to make an axle for my bike and this guy came in and asked him if he needed a stud girdle for his engine. The Ol' Man relied, "if you have to ask there are two things that come to mind, one is if you have to ask you don't need one or you are in over your head and should be paying someone else to build your engine for you."

The same can be applied to 4 bolt blocks, most of the engines that we see on here will never ever need any stouter lower end than came stock from the manufacturer and if they do need a stouter lower end they already know that they do or their engine builder does.

 

We ran a 67 Chevelle back in 74-76 it was a 327 +060 we had to run all GM parts we also ran a 6:17 gear, we ran at Lawerence KS. 1/8 mile and KCIR 1/4 mile, you do the math at KCIR with a 6:17 gear 28" tall tire. We replaced a lot of the so called Turbo heads, we angled milled them .200 and broke many many of them in the thinned out combustion area but never broke anything in the block even the stock rods with the HD rod bolts. Don't get me wrong we maintained the thing on a constant basis but never lost a lower end.

 

I'm pretty sure you are talking about small block chevy's so I'll kick my 2 cents which is what it's worth! Chevrolet ran 2 bolt mains on all the early motors 265, 283 and 327 all of which have strokes of 3.00-3.250. Even when Chevrolet went to large journals on the 327 they were still 2 bolt main blocks. I have had many claim to have the "rare" 4 bolt 327, but they don't exist short of installing a large journal 327 crankshaft in a 350 4 bolt block. I have run 283-310 inch small blocks 7500-8500rpm regularly and had very few if any issues with proper preperation. I think that Chevrolet felt that once they increased the stroke to close to 3 1/2 inches in the 350 that 4 bolt blocks may become a good idea. Couple this with their experience with big blocks of the time and their involvement in endurance racing in the late 60's and I think you have the background for 4 bolt main blocks.