[455firebird1969]

I used three technics during build-up of my 467 stock block bracket motor, all aimed at stress relief of this known weak link.

1. Flex honed the oil feed holes in the block. A clean hole will have less stress risers within.

2. Wire brushed the edges of the oil feel holes, rounding the sharpness, again eliminating stress risers.

3. Burnished the sharp edges if the block and caps that create the base where the bearing sits. A burnished edge is another form of stress relief, as the stress risers are smoothed over, minimizing places where a crack might start.

Casting flash and sharp edges are removed on the entire block, everywhere possible. Whether or not it makes a difference is up for debate. I think the extra time spent is worth the effort, when the engine is planned to make 700 HP.

[LMSRACER]

O.K. Here We Go...... I'm going to make multiple posts with many photos so give me about a 1/2 Hour to Finish.

First off is the 1971 455 Block Cast #485428 with a Date Code of B221.

It's unusual due to the Casting. It actually looks very much like a 1970 Cast #9799140 without the Two Outer Bolt Holes for Four Bolt Main. This Block is now Drilled and Tapped for 7/16" "Splayed Cap" Outer Bolt Holes.











More to Come,
Larry S.

[LMSRACER]

This is a 1972 455 Block with Cast #485428 and Date Code J291.

This is what I normally see when I look at a #485428 Casting. If you'll notice, this Casting in the Main Webbing Area is much different than the Casting in my previous Post.





O.K.... The Next Posts are going to Compare this Casting #485428/Dated J291 (1972) to a 400 Cast #9786133/Dated F077 (1967) and a 400 Casting #481988/Dated D211 (1971).

More to Come,
Larry S.

[LMSRACER]

I'm going to make two separate posts to show different views of the three castings.

This will be the first of the posts.

1972 455 #485428

1971 400 #481988

1967 400 #9786133

Front View of the #2 Main Webbing.

More to Come,
Larry S.

[LMSRACER]

Here's the Second Post regarding the visual differences between these three castings.

1972 455 #485428

1971 400 #481988

1967 400 #9786133

Rear View of the #2 Main Webbing.

More to Come,
Larry S.

[LPI]

Great Pictures Larry, Thanks!

Just a side note in post #204 the 1967 block clearly shows the "M" stamp on the pan rail.

That is a note to the assembly department saying that journal diameter is different.

Again great pictures showing the block casting changes from year to year.

[LMSRACER]

Here's a better visual utilizing a Straight Edge to show all of the Scalloped/Undercut/Thin Areas in the 400 Castings in Relation to the 455 #485428 (1972) Casting.

I'm going to make multiple posts to show a variety of angles for each Casting.

Here's the Passenger's Side Front View.

1972 455 #485428

1967 400 #9786133

1971 400 #481988

More to Come,
Larry S.

[LMSRACER]

Here's the Driver's Side of the Blocks showing yet again the Front View.
Keep in mind that all of these photos are of the #2 Main Webbing.

1972 455 #485428

1967 400 #9786133

1971 400 #481988

More to Come,
Larry S.

[LMSRACER]

O.k., now here's the Rear View of the #2 Main Webbing in the Three Block Castings.
First off is the Passenger's Side of the Block.

1972 455 #485428

1967 400 #9786133

1971 400 #481988

One more post to come showing a visual with the aid of a straight edge.

Larry S.

[LMSRACER]

So now here's the Rear View of the #2 Main Webbing on the Driver's Side of the Blocks.

1972 455 #485428

1967 400 #9786133

1971 400 #481988

O.K. that's it for the Visuals....
Now on to the Measurements.

Larry S.

[LMSRACER]

I'm going to make Several Posts that will not only Specify the Measurements, but will also Illustrate EXACTLY where the Measurements were made.

First off is the Cam Tunnel Area.



Results:
1) 1967 400 = 0.688"
2) 1971 400 = 0.688"
3) 1972 455 = 0.758"

Winner 455..

Larry S.

[LMSRACER]

Next is the Measurement directly below the Machined Main Bearing Saddle Area.



Results:
1) 1967 400 = 0.828"
2) 1971 400 = 0.826"
3) 1972 455 = 0.878"

Winner 455...

Larry S.

[LMSRACER]

Next is the Measurement Across the Main Bearing Saddle Itself.



Results:
1) 1967 400 = 0.976"
2) 1971 400 = 0.970"
3) 1972 455 = 0.970"

NOTE: The Machining of the Main Saddle on the 1967 Block was quite rough and therefore measured thicker than the others.

Results = Same..

Larry S.

[LMSRACER]

This next measurement is across the Block's Machined Surface at the Dowel Pin Location.



Results:
1) 1967 400 = 0.926" Average (Not Exactly a Straight Surface)
2) 1971 400 = 0.924" Average (Not Exactly a Straight Surface)
3) 1972 455 = 0.883"

Winner 400s

Larry S.

[LMSRACER]

This Next Measurement was made just below the Block Rail towards the Base of the Dowel Pin Area.



Results:
1) 1967 400 = 0.807"
2) 1971 400 = 0.805"
3) 1972 455 = 0.883"

Clear Winner 455
Larry S.

[PAUL K]

Good Job Larry! It looks like you might be debunking an old PY myth. Have you noticed any distinct difference in cylinder wall thickness between blocks?

[LMSRACER]

This Measurement is made across the Main Webbing at the Base of the Cylinder Bore. This area is just past the Cylinder Bore and is actually machined larger than the cylinder bore.



Results:
1) 1967 400 = 0.222"
2) 1971 400 = 0.185"
3) 1972 455 = 0.145"

Clear Winner = 1967 400
NOTE:
This Block also has some of the Thickest Cylinder Walls of ANY Pontiac Block that I have ever Sonic Tested.

This is where the 1967 400 Shines in My Mind.

Also, keep in mind that the Casting Lines in these 400 Blocks do not run up into the Dowel Pin Area of the Block the way that the 455 does.

So, along those lines of thinking, the 1967 400 is Probably the "Least Likely" 400 Block to Bust the Main Webbing out of the Block. (Through the Dowel Pin Area) Although, I don't see any reason to believe that it wouldn't be just as prone to Cracking down the Center (Up Through the Cam Bearing Oil Hole) as the 1971 400 Cast #481988 that I checked.

In Fact the Oil Hole that's Drilled from the Main Bearing Saddle to the Cam Tunnel to Supply Oil to the Cam Bearings is also Different between these two 400 Blocks.

Both Blocks have an 11/32" Oil Supply Hole that Steps down to a 5/16" Hole before the Passage Reaches the Cam Tunnel/Bearing. What's Different is that the 1967 has an 11/32" Hole with a Depth of 2.125" while the 1971 has the same 11/32" Hole, but it only has a "Drilled Depth" of 1.425" before it Transitions to the 5/16" Hole/Passage.

All that means is that there is a little more meat in that particular area on the 1971 Block Casting.

Next I'll point out what I meant when I said "Undercut" as it pertains to the 400 Castings.

Larry S.

[LMSRACER]

Let Me Point out the Areas of the Main Webbing that I called (Incorrectly) Undercut. I should have said Thin or Maybe Scalloped. I don't Know.......

Pictures are Worth a 1,000 Words......











These are All 400 Block Photos.

Larry S.

[LMSRACER]

My Intention Today is to show some of the Casting Areas that people need to look at when making a decision on which block to use.

Here's what I can tell anyone that wants to listen....

My Experience Is This:

There is No "Set in Stone" Rules when it comes to Block Selection. As I've shown, a Cast #485428 455, Both Cast in the Same Year, Date Codes B221 and J291 are ACTUALLY very different. Sure, One of them was Drilled and Tapped from the Factory for Four Bolt Main and the Other was never Drilled at all. What I MEAN is that the "Block Casting" is very different. The heck with the machining processes. The Castings are Different.

The 400 Blocks that I checked have Cam Bearing Oil Feed Passages of Different Dimensions. Who would have known that. In Fact I'd be willing to bet that if you checked Ten Different 400 Blocks that you would find that dimension to be inconsistent.
Don't get Me started on Cylinder Wall Thickness. That Dimension has been Different for every Block that I have ever checked. CHECK IT or wish that You Did.

I also showed that even though the 1967 400 Casting #9786133 has the same outward appearance as the 1971 400 Casting #481988, they actually differ greatly in their Main Web Thickness at the Base of the Cylinder Bores. That's not something that you can see by looking at the Block.

I'm not "Bad Mouthing" any of these Blocks. In Fact, they're some of the better Castings out there. I Know, they're not a SD455 Block or a Ram Air IV Block or a Ram Air V Block, but they're GOOD Blocks. I didn't pick any of the Newer Castings, such as the One that the OP Showed in His Initial Photos because those Blocks are Useless to Me.

Now, I've got a Question......
Has anyone ever measured the Main Web Thickness at the Base of the Cylinder Bore on an MR-1 or IA2 Block that has been Bored to 4.350" or Greater?
I'd love to know this dimension. I'll measure it myself as soon as I get the chance........

Have a Good Day,
Larry S.

[LMSRACER]

Originally Posted by LPI

Great Pictures Larry, Thanks!

Just a side note in post #204 the 1967 block clearly shows the "M" stamp on the pan rail.

That is a note to the assembly department saying that journal diameter is different.

Again great pictures showing the block casting changes from year to year.

So, What Does the Letter "M" Stand For?

Thanks,
Larry S.