[jamaca85]

just thought i would ask...wouldnt a block drilled for 4 bolt mains with two bolt mains be weaker than a block with just the two bolt mains with no provision for the 4 bolt mains drilled in it. for the block has no extra holes drilled in it, so this making it stronger on the bottom end? thoughts?

[mgarblik]

A two bolt block not drilled would be slightly better than a 4 bolt block drilled and run with 2 bolt caps installed. In that weak part of the block, drilling, taping and leaving the holes open removes valuable material and exposes lots of sharp edges to potential cracking in the iron at the threads. Personally, I would install 4 bolt caps or use a dedicated 2 bolt block. If you are planning to make 400-450 HP, and keep the RPM's below 5500-5800 RPM, I wouldn't worry about it either way. Not sure exactly why many, many Pontiac blocks were drilled and tapped and assembled with 2 bolt caps. Some old timer who worked in the engine plant during that time probably has the real answer. My guess is it had to do with availability of 4 bolt caps, the cost of changing the machining operation to make some 2 bolt and some 4 bolt blocks, or a last minute decision from some bean counter to save $15.00 per engine on lower output models which didn't really need the 4 bolt set-up. The cost of the larger caps and 6 additional fasteners would amount to millions of dollars in savings per year at the production levels Pontiac was running in those glory years.

[steve25]

I think you are right in terms of cost and time for the added holes even if they do go used as drilling and tapping 6 more holes with factory mass production set up's involves nothing more than loading 6 more drill's into the drill head , and 6 more tap's into the tap head, but the 4 bolt main caps themselves cost a good amount more as they where cast in ductle iron as opposed to plain cast!

[mgarblik]

I forgot about the material difference. Were all 5 ductile iron vs gray iron? That would make for a better bottom for sure. Many SBC's I have worked on when they get hot and spin a main bearing, they lose their register in the block. (no dowel pins). To fix those, I VERY CAREFULLY put the caps in a press and push on the center to spread them back out to restore the snap fit before line honing. You have to be super careful on a SBC with gray iron caps. They will fracture, extremely brittle. Ductile iron caps are almost plastic in nature and can be easily pressed back into shape on SBC engines equipped with these better caps. I would expect Pontiac caps to behave the same.

[steve25]

well I may have used the wrong term, all 5 where listed as being Armasteel, not ductile, but non the less better then gray iron!

[Tom Vaught]

Armasteel was not a steel material but a form of cast iron. Used on cranks a lot by Pontiac - A Trade Name started in the 1930s.

ARMA STEEL = PMI Pearlitic Malleable cast iron. ARMA STEEL logo may not be present on all cranks.
ARMA STEEL is not steel, but a form of cast iron. ARMA STEEL was registered trademark #0393916 GM used starting October of 1937. The trademark was last renewed in 1982 and expired in 2002.

Good info here (posted on the wallace site and other places).
http://www.wallaceracing.com/crank_info.htm

Tom V.

ps Any of the offshore "4340 material" may be ASSUMED to be better vs the old Pontiac cranks but the real test is how much of the material is contaminated with dirt, etc that makes the material weak due to the "voids" in the crank structure.

[ra5gto]

Jim Mino's race block that was used in all his cars since the seventies was a 4 bolt block with two bolt caps and no failures.

You have a better chance of getting poor quality machine work trying to do the upgrade than a failure from the original setup and you'll spend alot of money for nothing.

The best feature of the Pontiac engine is the design and quality of the factory machine work.

[racegto65]

Originally Posted by steve25

You can't just add studs and run without getting the line Bore checked to see if it has shifted, as Murphy's law will prevail here!

I've done it many times. No problems.

[dmac]

Originally Posted by ra5gto

Jim Mino's race block that was used in all his cars since the seventies was a 4 bolt block with two bolt caps and no failures.

You have a better chance of getting poor quality machine work trying to do the upgrade than a failure from the original setup and you'll spend alot of money for nothing.

The best feature of the Pontiac engine is the design and quality of the factory machine work.

Speaking about the quality of work- racegto65 sent me a used front cap after I posted a pic of the original I had with the 'ear' broken off at the pin/dowel.

The cap he sent lined up perfectly at the parting lines and when placed on a flat surface, the height of the bore felt identical. It is as close by touch in fit as the remaining caps. That goes for the face of the cap from front and back of engine.

I know I need to have it checked but I think this shows something about the quality of the machining on these old pontiacs. Maybe the front main cap is going to be closer simply due to starting at the front, and caps for the other mains might not have been so close. But the fact that the machining is that close, but on my engine and others, caps were broken very similarly at the dowel pin, apparently from the factory, shows a lack of concern over areas other than the machining. I think the engineering of the Pontiacs was probably top-notch, but the assembly work/QA maybe not so much.

That said, thanks to racegto65 for sending the cap. I hope to save at least a couple hundred dollars by avoiding the align bore, and using the two bolt caps. If I was going to need an align bore, I was going to go ahead and replace all the caps, so this free cap that apparently will work is going to save me $600, maybe more since now, without new caps, I'm not going to use a new crank either. Posts confirming the reliability of two bolt mains for sub 500 hp leaves me comfortable.

I was facing what others always face- If you are needing to do this, you may as well do this while you are at it. For us on tight budgets, mission creep can be a huge issue. A simple rebuild can explode into a $6000 new engine and add months or years to just getting a car back on the road.. IF this free cap works out, I will be back on track to spending about $2500 for a short block. New rods are a definite, as are new pistons, oil pump, timing gears/chain.

Thanks to everyone who has replied to both my posts on my main cap issues.

[hurryinhoosier62]

Originally Posted by steve25

You can't just add studs and run without getting the line Bore checked to see if it has shifted, as Murphy's law will prevail here!

X 2. Since studs can cause the saddle bore diameter to actually tighten( I’ve personally seen as much as .0015) it’s a good idea to install the stud per manufacturer’s recommendation, torque the main caps and measure the new saddle sizes. Don’t be surprised if it indicates the saddle needs to be align honed to be in spec .

[hurryinhoosier62]

Originally Posted by racegto65

I've done it many times. No problems.

You got lucky...

[hurryinhoosier62]

Originally Posted by Tom Vaught

Thrust Cap can really bite you in the butt of it is wrong.
Especially if the customer bought a block and the thrust cap was machined wrong somewhere along the line. We are talking Leaning Tower of Pisa here (when the bolts are vertical) and the thrust surface is leaning front to back.)

Tom V.

Yep. I’ve had to fix a few of these over the years. The best way to avoid the situation is to install a modified thrust bearing in the cap while grinding it . This way, the cap can not be cut with a tilt in the mating surface.

[steve25]

Racegto65 if you have done that swap many times and gone racing without checking things then you owe your guardian Angel's a pay raise big time!!

[PAUL K]

Originally Posted by 64speed

I have the two 455s that I bought a while back and had Both of them cleaned up and checked at the machine shop to make sure both were viable candidates for rebuilds both passed the test and said they would clean up at 30 over but one has the factory main caps and one is missing it’s set.

You told me the block without the caps was cracked and not useable??

[Rocky Rotella]

Just wanted to point out that not all 4-bolt caps were a special alloy. Most 3.25-inch units were standard gray iron. Only a handful of 3 and 3.25-inch caps were special.

[Tom Vaught]

After a while, when you get old, you can't remember what day it is, much less what we said in a conversation. Give us old guys a break, Paul. (;>).

Tom V.

[Tom Vaught]

Originally Posted by Rocky Rotella

Just wanted to point out that not all 4-bolt caps were a special alloy. Most 3.25-inch units were standard gray iron.

I was told only the 421 SD caps were different material.
I was told that Arnie had some race blocks that Tom Nell supplied to him that had "Special Caps".
I saw an engine at Butler's, one of Arnie's blocks, that had splayed factory caps. Assume they were special material.

99% of the Production Pontiac engines I have looked at over the years looked like the caps and the block were identical material.

Tom V.

[Rocky Rotella]

Tom V,

I can't speak on the 421 SD caps, but I'd highly suspect you're correct.

And I'm sure Arnie had the proper connections (Tom Nell!) to get anything that would have helped durability!

There were definitely some special 3-inch 4-bolt caps (R/A V, R/A IV, etc.) that were PMI (Arma Steel).

The SD-455 had special 3.25-inch main caps constructed of ductile iron. That same alloy was used for the 3-inch caps on the NASCAR 366 block. Both were 4-bolt obviously.

While anything is possible, I believe the vast majority of standard production 421, 428, and 455 (including 71-72 455 HO) 4-bolt caps were constructed standard gray iron.

[Rocky Rotella]

And to clarify, whatever material/alloy the center three caps were constructed of on a given engine always applied to the front and rear caps.

Pontiac's main caps were cast as a single unit, rough machined, cut apart, and finished. They were then installed on the block, the crankshaft bore was machined, and the block/caps were treated as a matched/machined assembly.

Pontiac never offered block castings or main caps separately.

[johnta1]

Pontiac's main caps were cast as a single unit, rough machined, cut apart, and finished.

Like a loaf of bread?

Interesting info.