[trifive]

I have always heard that everyone wants a 4-bolt main, rather than a 2 bolt main.

To me it doesn't matter.

I am sure I will get tons of lectures on this issue.

But here is my reasoning, I have seen people break rods, pistons, cranks etc, But I haven't heard of anyone ever braking a main cap because it was a 2 bolt cap instead of a 4 bolt cap.

So lets have all the discussions on this issue.

Otis

 

[belairrudy]

:confused0006: I think the purpose of the four bolt was to keep the bearing from spinning.

 

[trifive]

I thought that the bearings only spun when the crank was bad, or loose rod nuts, bad bearings etc? I haven't heard of bearings being bad due to 2 bolts v 4 bolts.

I really don't know the answer though.

Otis

 

[belairrudy]

Neither do I... But I'm sure we will find out.

 

[aafc1]

Hi, The reasoning for four bolts caps is so on high horsepower [600 and above] and high revving engines will keep the harmonics in check. Otherwise these engines would vibrate themselves apart.

 

[r66ss]

Hi, The reasoning for four bolts caps is so on high horsepower [600 and above] and high revving engines will keep the harmonics in check. Otherwise these engines would vibrate themselves apart.

basically hes right on , even tho Ive seen and actually have( 2 ) 4 bolt and (2) bolt big block motors
The 2 bolts been spun to 6 thousand rpms occisionaly and still holding up, the 496 is naturally a 4 bolt motor.

 

[bowtieblue57]

blocks

i have to agree with several of the guys i have being building race engines for over thirty years and it all boils down to hp and compression if you build a 9.1 compression motor no need of 4 bolt main it's overkill but if you are going to build a 13.1 compression motor a lot of changes go on in the motor the pressure increases putting more pressure on the bearings and this is when the extra bolts help keep everything in place this is why high dollar blocks all come with 4 and now even 6 bolt main blocks
thanks hope this helps
bob

 

[mickeywestsr]

I have friends that run "round D round" racing and they don't prefer one over the other.

 

[Rick_L]

The purpose of 4 bolt mains is not to keep the cap together because it's fine. The purpose is to spread the load out in the block to keep the bolt holes in the block from breaking.

I had a 316 cubic inch drag race engine years back that was built using a 283 2 bolt block (they all are). It made about 525 hp and was spun to 8000+ rpm. It ran fine with no troubles and I ran it quite lot for about half a seaon. I tore it down to hone and re-ring it, as was normal practice. While unloading the block out of my pickup, my engine builder's eagle eye noticed a crack adjacent to one of the main cap bolt holes. Turned out that the main webs were cracked at the bolt holes on all 3 center caps, 12 places in all (fore and aft on each bolt). So much for honing that block, I ended up getting another block machined and put aftermarket 4 bolt caps on it. It ran perfectly after that, and I had 4 bolt mains on every race engine I built or used after that.

I think it's the rpm that kills them, not the power. But it really doesn't matter because power and rpm go hand in hand.

So I would recommend 4 bolt mains for any small block that turns over 6500-7000 rpm regularly. I've never had a big block performance engine that didn't have 4 bolt mains, but I think the same guideline would apply.

And you're right Otis, spinning bearings generally has to do with oiling, having the proper crush on the bearings, and the proper bearing clearance and crankshaft finish. But if you run an engine with cracked bolt bosses, you are losing crush, and that could lead to a spun bearing. In my case the bearings were still fine because it was caught soon enough.

 

[finallyhavea57]

Thanks for this post Otis! Never new the difference and never got around to asking. I guess with my driving it doesn't make a difference which I use.

Nice to finally know though.

Don

 

[moses]

I've seen 4 bolt break in between the bolts where the step is and I've seen 2 bolts take over 750HP in a 4000# plus car for over two yrs of abuse so to me its the luck of the draw.

 

[56owner]

Stressed OUT??

I've seen 4 bolt break in between the bolts where the step is and I've seen 2 bolts take over 750HP in a 4000# plus car for over two yrs of abuse so to me its the luck of the draw.

Or maybe stress incured during maching?? Back in the day World of Outlaw sprint cars could use stock 400 block and crank but were uually replaced at 9-13 races.

 

[CNC BLOCKS]

On the 350 blocks if we are building an engine over 400 horse we will start with a 4 bolt block and if we can fined a 2482 cap that is what we prefer.

A 2 bolt with a 3.480 stroke and 400 horse will live but add a 3.750 crank to the block and we have seen the caps move as the added stroke will add side load to the caps.Here is a link. http://www.ls1tech.com/forums/advanced-engineering-tech/652566-never-seen.html

Plus we build alot of circle track engines some 2 barrel we use only a good 4 bolt block as we have seen that a 2 bolt will not stand up for a season and these engines turn about 6500 to 6800

I have a 5 gallon bucket of old caps that have walked in the registers or have broke. here is another good link http://forums.corvetteforum.com/c4-...425-eagle-4-bolt-billet-main-caps-1992-a.html


We deal with a couple hundred blocks a years and problems guys have with blocks because they read in a book that two bolt 350 was good for 500 horse. HMMMM

Then you have the guy who builds one engine with a 2 bolt mains and lasted for 5 years give me a break:sign0020:

If you have alot of time to read this is another good link.
http://www.chevelles.com/forums/showthread.php?t=38173

Plus there is always the guy that says add studs and since when does studs make the caps stronger its still a grey cast cap with better hardware!!! Doesn't really do anything to make the caps stronger.

Again we deal with blocks every day and we probably see more issues with them then people.

We use to install alot of splayed caps on OEM blocks both 2 bolt and 4 bolt blocks but since Dart came out with the SHP that seems to be a block of choice and that block is rated at 600 horse and for some one to say a OEM stock block is rated the same. That would hard to believe.

Look at a GM catolog and see what GM rates their blocks at as they have done alot of testing on their stuff.

We have run the 2482 caps blocks that have sonic test good in some 525 horse applications and have worked out fine and any more then that we have gone to a splayed center caps billet front cap and strap the rear main cap.

 

[CNC BLOCKS]

I've seen 4 bolt break in between the bolts where the step is and I've seen 2 bolts take over 750HP in a 4000# plus car for over two yrs of abuse so to me its the luck of the draw.

I hope you are talking a BBC 2 bolt!!

 

[56owner]

HEY CNC BLOCKS

hAVE YOU ANY EXPERIENCE WITH BLOCKS THAT WERE STRESS RELIEVED ON A SHAKER TABLE . WONDERING if ITS WORTH THE TROUBLE?

 

[Rick_L]

56owner, I'm not CNC, but I can comment.

I had a Chevy Bow Tie block stress relieved in an oven at my engine machinist's suggestion. I had no problems with it except it came back with a nasty brown color. This was a good while back. The block was the one they sold back then that was finish machined except the bores.

The next block I built did not get that treatment. It was the same style casting except that we finished it with a smaller bore.

I never had any problems with the align bore or crankshafts in any race engine except that 2 bolt one. But you have to remember I was drag racing. Circle track racing is another step up due to the number of cycles put on the engine, though we drag racers tend to run more rpm.

Seems to me that there is no way a shaker table can impart the same forces as actual use, even with an elaborate fixture.

We fooled around with oven stress relieving for some large industrial vibrating equipment in my real job. Personally I was always suspicious of any benefit.

 

[HIGH ROLLER]

Ron Hutter was making in excess of 650 hp with a stock block before CNC machines were even made..http://web.a-znet.com/~dave1w/putting.htm oh i no this is some internet story well thats bs, before Bow tie blocks were even though of to.

 

[737Pilot]

I would have to ask what are/were the condition that the motor was being used. I have spent hours on the internet reading about this as I am looking for a 350 to build for my 56.

Some will have you convinced that a 2 bolt will barely hold together over 351hp and others will tell you they drag raced for 95 years with a 2 bolt with no issues.

The best quote I found on the 'net somewhere was "4 bolts are for people who can't sleep at night!"

 

[CNC BLOCKS]

Ron Hutter was making in excess of 650 hp with a stock block before CNC machines were even made..http://web.a-znet.com/~dave1w/putting.htm oh i no this is some internet story well thats bs, before Bow tie blocks were even though of to.

Thats interesting as I was making over 650 horse with some of my engines I have built over the last 38 years and some were before I had my CNC machines. Interesting though!!!

 

[CNC BLOCKS]

I would have to ask what are/were the condition that the motor was being used. I have spent hours on the internet reading about this as I am looking for a 350 to build for my 56.

Some will have you convinced that a 2 bolt will barely hold together over 351hp and others will tell you they drag raced for 95 years with a 2 bolt with no issues.

The best quote I found on the 'net somewhere was "4 bolts are for people who can't sleep at night!"

I have been around engines enough to see what has worked and what has not worked, Intersting on a 400 two bolt block GM left the center main wide because of the added stroke.

I wish I kept track of all the 2 bolt blocks we have had to put splayed caps on because they were fretting in the registers.