I have a Question. Why does every one worry about a block having a 4 bolt main. Just my thinking, If a motor is turning hard enough to brake a main cap, does to bolts to the far out side of center really help. The only couple of broke main caps that I have seen broke in the middle. And the crank was also broke. So why is 4 bolt so important and coast more? If a motor is making that kind of power wouldn't a bridge on the cap be more help than two bolts to the outer edge. May be you can help me learn some thing, thanks
Bolts are, esp. when torqued, a stiff spring. Four per cap, 2 at an angle, serve to stiffen the assembly.
Some people touting 4 bolt mains tend to forget or ignore what happened to 4 bolt main Chevies when first raced in NASCAR. It seems that the 4 bolt caps were thinner in the center and when dynamic forces came into play, the crankshaft would be forced down ever so slightly causing the a ring to pinch the journal and bang , lost motor. They cured the problem by counter boring the block and main caps and inserting stainless bushings that prevented cap walk. The street and drag race guys never saw that because they never experienced long periods of high speed dynamics. The best 4 bolt blocks are ones with aftermarket splayed main bolts that draw the bottom end together and counteract the high speed dynamics. The 4 bolt in my El Camino became dreadfully tired and needed sleeving which I didn't want to spend money on. I bought a '69 Chevelle 300 hp 2 bolt block and for over 270,000 miles , beat the snot out of it. It's tired now but never a hint of main or rod bearing problems. In my opinion, 4 bolts are nice but a well built 2 bolt delivers all you need.
Back in the previous century, when I was building sbc s I read everything I could about them. Don’t chisel this in granite, but I belive it was Smokie that said you don’t need four bolt mains till you get over 600 horse power.... and very few people can get 600 out of a small block. Now before you jump on the horse power figures ... this was in the late seventies. But 600 back then, is the same 600 today. Just my recollection. Bones
In my Chebbie days the best blocks I found were from C60s . Under the timing cover was .020 not .010 cast into the block . High Nickle 4 bolt block . There have been many 2 bolt blocks regularly spun to 10K . I really would not worry too much about finding and spending big money on a 4 bolt block , it’s not needed for the driving habits 99.9 % , most of have lived to see . I have a Cummins 4 cyl Diesel in my Power Wagon daily driver that I bet is getting way more pounding on the crank every day than most gas engines will see in a lifetime , it’s a 2 bolt block with 2 1/4 in wide bearings . Don’t stress over stuff you don’t need to .
Splayed caps actually work. Straight 4 bolts weaken the main webs. Studded 2 bolts are plenty strong. There are differences in factory cap material (Nodular Iron vs Grey Iron) No offense, but that High Nickel production block myth was debunked by people that worked at the foundry.
I agree with tomcat, the current GM race blocks use nodular main caps but they don't mention the old Bow Tie ( I think it was late '70's- early '80's) High Tin blocks anymore that were available under p/n 366246 and there was also p/n 366287 that had siamesed bores and thick cylinder walls. I always found it interesting that Jenkins or Yunick never mentioned the 010/020 thing, I imagine that was so they could keep a ready supply of blocks for themselves. Vizard did mention it in a book of his and he says the percentage of tin was 10% but Google has a metallurgical paper written by a professor that says tin can be alloyed with cast iron on the order of 1 or 2/10's of a percent. That is a far cry from ten percent.
Again thanks for a correction notice. I quess I fall in the you can’t fix stupid line , concerning nickel content of a SBC . Im sorry if I mislead anyone, just passing on what I was told, many moons ago. I haven’t touched any BowTies in years , I suspect it is because there are so many NASCAR , High Nickel blocks floating around , I just wanted to be different and try an engine out with the distributer on the wrong end of the cam and it only has a lowly 2 bolt main cap block also. It really seems to work as well as the high dollar stuff , I looked for many years ago . Again don’t stress the small stuff , dare to be different and use what you have, all for the cause of having fun with your car .
All of the above, otherwise a 4-bolt block is little more than bragging rights. My 355 is a 2-bolt block and I used all ARP hardware to assemble it, Scat rods with 7/16" bolts. We used 2-bolt blocks in the stock cars, wound those up to 7k a couple nights a week.
6-bolt mains on my dad's 1975 Mercedes-Benz V8, too. Four vertical and two horizontal. I was surprised to find 4-bolt mains on the little Alfa Romeo Alfasud flat-4. Unusually for a horizontally-opposed engine the iron block is one piece, with conventional bearing caps except in that they are cross-bolted through the bottom part of the block.
Big 3 did not spend many $$$ making 4 bolt mains just to spend the money or train engineers, they ARE more stable. As many have stated 2 bolt mains are up to the task 99.9% of the time. I certainly would not take a good running 2-bolt block out of a vehicle to put in a 4-bolt just so I could say I had one.
Chevy made far more truck 4 bolt main engines, than car 4 bolt main engines. What is it about trucks and high performance cars, that would make them think the extra parts and machine work of adding extra bolts, would be worth the effort?
Thanks for all the replies. I just see motors for sale and people want more for a 4 bolt than a 2 bolt and wonder way the different s and is it really worth more.
If I was going to build high horsepower, which translates to high bucks, I would invest a little more at the start by selecting a four bolt main. A small cam, headers, high rise, Four barrel.... two bolt would be fine. Bones
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