[LMSRACER]

Originally Posted by grandville455

I talked to my machinist today and he said same thing, He wants the most straight down clamping force possible, and will sometimes ream out caps .030-.060 so there is absolutely no side pressure on the shoulder of the bolt and its all on the washer!...

You may already know this, but it's imperative that when you assemble your engine, that you do so with the "Same Exact" fasteners that were employed during the align boring and honing process. In your case, the Grade 8 Bolts that were supplied by Butlers.

ARP Studs don't stretch as much, (when torqued to the same specification), providing greater clamping forces, and the body of the stud tends to be larger in diameter than the body of the bolts that were used. That last part pertains to, and is in relation to, the size of the hole that your machinist has reamed into the main caps.

Your machinist is 100% correct and having the outer "Splayed" holes drilled into the block at the exact angle/centerline as the Main Caps is critical. Although, believe me when I say that I've seen it done wrong.

Have a good one,
Larry S.

[GRX]

Great job Larry. The pontiac community is all the greater because of your efforts.

If I may ask ... have you noticed if the casting variances you mentioned relate in any way to the foundry numbers? (GME, GM5, GM10, etc ...) Would make identification of desirable blocks in fully assembled engines much easier if true.

[LMSRACER]

Originally Posted by JD311

I thought 7/16 would be fine as well. So should I send these back and get the 7/16 drilled caps? Or can I use these 1/2 in drilled caps and have the block drilled for 7/16? I think you can get arp bolts with a bigger head.

Well, I'd prefer the Caps with the correct hole size and the ARP Studs.

I like that the "Mating Surface" of the Main Cap, with the Smaller "Though Hole", is Greater and therefore contacts a Larger Area of the Block Mating Surface. I also prefer to have the Edge (Inside Diameter) of the Hole in the Main Cap closer to the (Outside Diameter) Threaded Hole in the Block Surface.

Larry S.

[LMSRACER]

Originally Posted by GRX

Great job Larry. The pontiac community is all the greater because of your efforts.

If I may ask ... have you noticed if the casting variances you mentioned relate in any way to the foundry numbers? (GME, GM5, GM10, etc ...) Would make identification of desirable blocks in fully assembled engines much easier if true.

Well , I can tell you that the 5 Blocks that are here in the Shop have 5 Different Block Codes. GMC, GM1, GM3, GM7 & GM8.

I've concentrated on Block Dates, Casting Numbers and Applications. (Such as, 2Bbl. or 4Bbl., Low Performance or High Performance, Etc.)

I believe that in order to be able to determine a correlation between Block Castings and "Pontiac Foundry Casting Line Coding", that it would take a Large Number of Blocks with the same Block Casting Number and Different Build Dates. Then you could analyze the Foundry Codes to see if there's a trend.

I've never had enough Blocks with the same Casting Number to do that accurately.

If you get it wrong, then you may end up passing on a Good Block.

It is a Good Idea and It could be done with a combined effort on the part of the PY Forum Members.

Larry S.

[grandville455]

Originally Posted by JD311

I checked my program splayed caps and they are drilled for 1/2 in as well. Looks like it would still work for the 59 block I have though. I have had these for awhile and just noticed it. Wonder if I should try to send them back or use them?

Thats exactly what my guy did, just drilled and tapped it for 7/16"...

[JD311]

Are you using the"regular" dowels or just the ones around the studs now?

[Chipped Tooth]

Just my 2¢ but wouldn't it be beneficial to eliminate the dowell pin and step the cap surface block side then take the extra material off the cap?

Oh BTW I'm still working on my girdle setup.

[BruceWilkie]

No... dowels stop movement in all directions stepped only stops movement in 2 directions. Fore/aft control just as important as side to side.

Dowel fitment is important... I'd say critical on high powered high rpm engines.

[Chipped Tooth]

Agreed, hence my girdle plans.

But it also seems a dowel pin is a excellent source for a crack to start..... Obvious in the 557 blocks.

The dowel pin design that surrounds the study seems like a better option than drilling into the main webbing.

[Tom Vaught]

Big Block Chebbys have a "registered main cap" that Keeps the main cap from moving side to side. Deal is it doesn't really work vs a dowel set-up.

When the main cap sees a high load, the high load causes the center if the main cap to get "taller" vs stock and the edges of the main cap move inward. This means that the main cap "register" now has even more slop to it when using vertical 4 bolt mains or a 2 bolt main block.

A Pontiac block uses dowels but the dowels are typically loose and the cap can still move around under load.

A IA-2 (All Pontiac) Block has the chevy register but uses splayed outer bolt caps that when tightened pull the cap tighter to the block register. They also use dowels that keep the cap from moving front to back under load.

The old 59-60 type blocks used a much thicker cap (top of cap to block surface) so the cap could bow upward less vs the later caps, (as mentioned earlier).

In my mind the hot set-up is select fit and longer dowels along with splayed capson a two bolt main factory block for the low buck deal. Use 7/16" fasteners on the ends of the splayed caps as that means more block meat surrounding the 7/16" bolt vs the larger 1/2" bolt.

Tom V.

[Tom Vaught]

Originally Posted by Chipped Tooth

The dowel pin design that surrounds the study seems like a better option than drilling into the main webbing.

"Study" Probably a fat finger and you meant stud. I do those occasionally or the PY spelling deal does it for you and you do not notice.

But back on your "Timing Cover Ring" around the stud or bolt deal.

To make that work you need to counter bore a precision pocket for the ring to sit in.
Not a big deal with the machining except you now created a "step" in the cap hole in a very high stress area of the cap. Much easier to use a normal longer dowel register and be able to finish hone the hole for a very smooth bore and no stress risers vs the step in the cap deal.

Food for thought. This is not a timing cover.

Tom Vaught

[Chipped Tooth]

I understand what your saying on the cap getting taller.

I still think the register design is a better option for a weak webbing block instead of drilling a hole for a pin.

I also believe the extended skirt block design is the best for a performance application.

[Chipped Tooth]

Yes I missed the study...... Spell check LOL

I don't agree with your timing cover theory.......

Reason is lots of performance connecting rods have this feature..... I think rods are a higher stressed item than a main cap.

But I'm not saying I'm right.

[JD311]

I called pro-gram about my caps being drilled for 1/2 in. Apparently they used to make the outer bolt holes 7/16, but the input they've gotten in the last few years was to make them 1/2 in. They can custom make 7/16, but they all come 1/2 standard now. Had a lengthy conversation on the phone. He also noted Pontiacs had two different dowel sizes, .309, and .3125 (5/16). My blocks all measure 5/16, their caps are 5/16 as well. He said I could still use them for 7/16 by using a insert like a t bolt washer. (like something you use on a 302 ford with 7/16 bolt holes and a 351w head with 1/2 in bolt holes. They also do main spacers for Pontiacs using 351c bearing.

[LMSRACER]

Originally Posted by JD311

I called pro-gram about my caps being drilled for 1/2 in. Apparently they used to make the outer bolt holes 7/16, but the input they've gotten in the last few years was to make them 1/2 in. They can custom make 7/16, but they all come 1/2 standard now. Had a lengthy conversation on the phone. He also noted Pontiacs had two different dowel sizes, .309, and .3125 (5/16). My blocks all measure 5/16, their caps are 5/16 as well. He said I could still use them for 7/16 by using a insert like a t bolt washer. (like something you use on a 302 ford with 7/16 bolt holes and a 351w head with 1/2 in bolt holes. They also do main spacers for Pontiacs using 351c bearing.

The Main Caps that I sent back were drilled 1/2" and the Main Caps that they're sending back are to be drilled 7/16". Like I said earlier, it's a preference thing. I listed why I prefer the smaller holes already.

Question:
What Year did Pontiac switch to 0.3125" Dowels?
I've checked many over the years and most of the time, I get 0.3090" to 0.3095".....

Another "Repeat" Question:
Let Me ask again, Has anyone actually measured the Main Webbing Thickness at the Base of the Cylinder Bores of an IA-2 or MR-1 that has been Bored 4.350" or Larger?
If so, then what was this Dimension?

Have a Good One,
Larry S.

[JD311]

We have an IAII in a car right now, I never measured it. Its bored to 4.35, it looks thick lol.

[LMSRACER]

O.K., I just checked Three Different Blocks for Dowel Pin Sizing.
1967 400 Block = 0.309"
1971 455 Block = 0.309"
1974 350 Block = 0.309"

The 1974 350 Block is the Newest Block that I currently have.
So, the Question is:
If Pontiac Changed over to a 0.3125" Dowel Pin, When did it Occur?

Regarding the Question on the IA-2 and MR-1 Blocks:
On an IA-2 or Mr-1 Block the Thickness Between the Bores at the Deck Surface is approximately 0.270" @ a 4.350" Bore. Therefore, I know that it is going to be Less than that at the Base of the Cylinder Bore. I'll bet that it is "Considerably" Less....

Larry S.

[gene simmons]

Larry,
I had a 1974 400 #481988 that the main web was cast with a notch,to clear the dipstick tube. It appeared to be one year only. None of the 67-78 blocks that i have seen had this.
Does your 74 350 have it, and if it does,do you have a photo?

If you were to drill for 4 bolt,the bolt hole would be thin on the dipstick tube side.

[Tom Vaught]

1)

Originally Posted by Chipped Tooth

I understand what your saying on the cap getting taller.

2) I still think the register design is a better option for a weak webbing block instead of drilling a hole for a pin.

3) I also believe the extended skirt block design is the best for a performance application.

1) Taller cap, more material at the bridge, more strength and less deflection

2) No factory Pontiac block has the cap register design (same as BB Chebby).
Your "register" is actually just a hollow dowel and has less strength vs a solid dowel.
Very easy to mod a cap and block for a 5/16" (.312) tall solid dowel vs machine for a 'ring" that effectively takes away some of the clamp load surface area on the block and the main cap. So the design is flawed.

3) I agree that an extended skirt is stronger. Even a 3/16" extended skirt (like the one added to the All Pontiac Block). In a perfect world you would have a Hemi deep skirt or Ford Deep Skirt design and a cross bolted 6 or 4 bolt attachment design. but most are in love with the Pontiac/chebby design as it is traditional Pontiac/GM design.

Tom V.

ps I have never seen a 5/16" dowel (.312) as stock on any pontiac block or any print showing that larger diameter dowel pin.

[Half-Inch Stud]

Originally Posted by Chipped Tooth

.....
Reason is lots of performance connecting rods have this feature..... I think rods are a higher stressed item than a main cap.

But I'm not saying I'm right.

Driver side Rear Axle Cap/Bolt had the toughest duty. See how thry run.