[Formulas]

If the deck is to tall to start with the heads should end up where they were supposed to be in the first place

[Formulajones]

There are a bunch more reasons to deck a block other than just trying to get the piston near the deck height.

Surface finish is one depending on the head gasket planned, but the bigger reasons are to get the darn thing square in the first place.

I've had brand spanking new blocks that weren't straight, and most all of your factory stuff will not have a straight deck surface. I've had them higher on one end than the other and even twisted from end to end several thou. This alone will determine how much needs to come off in the first place, then worry about piston to deck clearance and what you're willing to do there.

Decking the block is just a normal part of the engine building process as far as I'm concerned if for nothing else just to make sure it's square. Even the last 455 I built that didn't have but a few thousand miles when it came to me from another builder, I went through again for a member here, and even though it had been decked, it was not square at all, and Paul took a fair amount off to correct that thing.

What I haven't seen or experienced yet, is after a proper deck surface is established and that engine is run for years and 10's of thousands of miles and thousands of heat cycles, does the deck surface move? Is it going to need another correction? I haven't revisited that myself with my own personal engines. If it does, did you achieve zero deck by moving the piston pin height or did you shave the block a bunch? Is there enough left to clean it up?
Maybe it's smart to leave the pistons .005" down for some wiggle room. Or maybe you just want to order custom pistons and move the pin height.
I would certainly hate to back myself into a corner the next time I have to go through the engine. Just things to think about.

[Cliff R]

Main bore diameter divided by two added to the distance from the edge of the bore to the deck......I hope I got that right it's pretty early in the morning and my coffee isn't done brewing yet!.....

[mgarblik]

We have a squaring fixture like most shops that corrects the deck to the cam/crankshaft centerline. Every block is different but speaking in generalities, Pontiac blocks are better than the average iron V-8 vintage block. I think the very worst Pontiac I have personally squared was .009" out of square. Typical is .003-.004. Worst blocks as a group are the old school SBC ones cast in Mexico! All I can say is WOW! Had one last year from a student that was .021" out of square. High on one end , low on the other, twisted to hell and back. I made him re-set it up in the mill 2 times before I really spent a bunch of time with him. Was sure he had something under the parallels or in the main pucks. Nope, just a terrible Chevy piece of junk. As expected, we had issues with the cam tunnel as well. It turned out OK after a bunch of work.

[Formulajones]

I've had cam tunnel issues with Pontiac and Chevrolet, Ford not so much.
Just seems like the decks are always out of square no matter what brand engine it is. Even brand new blocks.

[hurryinhoosier62]

[QUOTE=track73;6413924]

Originally Posted by Cliff R

I don't do either but it's still a good plan.

I will NOT use a block that needs line bored/honed. If the block has "moved" or not thru thru the center of the main bores or other line bore issue or problem, and the crank doesn't turn freely with two fingers (no rear seal installed) I woln't use it.

When I started the Pontiac hobby I read the HO "bible". It says Pontiac blocks rarely need Line boring.

Align boring and align HONING are two entirely different machining processes. I would agree on align boring. Align boring should be left to main cap replacement or saddle repairs after a spun bearing.

[tom s]

We have seen more cam tunnel issues with 455 blocks.Tom

[lust4speed]

Don't think anyone has mentioned that the magic number for the main journal size is not the 3" or 3.25" since that diameter is the crank, and the bearing thickness and running clearance is also in that number. Someone please confirm my numbers but pretty sure the radius numbers I use are 1.595" for three inch mains and 1.720" for three and a quarter inch mains. Too cold to get out to the garage to dig out my notes.

While I do my measuring with a 12" caliper, I prefer the setup the machinist uses. I figure that if we agree then neither of us probably made a mistake. Corny, but measure twice, cut once applies to more than carpentry.

I would agree that the 455 block cam tunnels are the worse, but most of the tunnels are always out a little bit and require just a very minor touchup with the cam bearing tool. Also agree most original Pontiac blocks are within .004" and the only disasters I've seen have been previously decked blocks and some of those remind me of ocean waves. I rebuilt a friend's original 1972 455 H.O. block that was previously rebuilt by a "race shop" in Los Angeles and I swear it looked like they decked it with a belt sander.

[Formulajones]

Originally Posted by lust4speed

Don't think anyone has mentioned that the magic number for the main journal size is not the 3" or 3.25" since that diameter is the crank, and the bearing thickness and running clearance is also in that number. Someone please confirm my numbers but pretty sure the radius numbers I use are 1.595" for three inch mains and 1.720" for three and a quarter inch mains. Too cold to get out to the garage to dig out my notes.

.

Been a long time since I talked to Paul about that subject but if I remember any of it at all, it seemed to me that he likes a certain amount of bearing "crush" and a favorite brand of bearing that holds it's shape better (doesn't go out of round) In the end better bearing "wear" Of course the cap and block need to be perfectly round.
So with that almost always involves cutting the caps and align honing. Especially when the bolts are changed to something that torques differently.

As far as dimensions, each machinist is probably different in what they like to see. I don't remember those specifics but that's why I pay Paul to do it

[Ram Air IV Jack]

Originally Posted by Cliff R

I don't do either but it's still a good plan.

I will NOT use a block that needs line bored/honed. If the block has "moved" or not thru thru the center of the main bores or other line bore issue or problem, and the crank doesn't turn freely with two fingers (no rear seal installed) I woln't use it. I'm NOT saying here there is anything wrong with line honing and such, I've just had a few issues with machine shops NOT doing a good job and throwing more problems into the equation. In other words, from what I've seen with this sort of thing is that it's better to trust the work Pontiac did 50 years ago vs what a machine shop is going to do for you today. It's also rare to find a Pontiac block that isn't true thru the main bores right to start with. In all the years I built them can only remember a couple that didn't make the grade in that area. Same with having crankshafts machined. More come back WORSE than when you sent them out, so do your homework in that arena before you send out a crank that needs more than just polished and put back in service. I was actually lucky in that deal as I found the BEST crankshaft machinist on the planet early in the game and used him for every single engine I built here with absolutely ZERO issues anyplace. Sadly, like many other folks who do excellent work he retired a few years back, which was fine with me because I was done with engine builds anyhow and had also moved on to other things that pay the bills with a LOT less effort on my part.

Anyhow, back to zero decking. I used to have the blocks bored, bring them back to the shop, then go thru the process of mocking things up to determine how much to remove when decking/squaring for zero deck height. Of course that can lead to some "oh-chit" scenarios if you happend to buy pistons that were a bit shorter than they should have been!

Got better at it over the years and did the math instead. This simply involves measuring cranksahft center line to the existing deck and buying rods and pistons that would only require a small amount removed from the deck to square things up. This means only one to the machine shop instead of two. Of course you need to double and triple check your math, but every single build I did in that fashion came out dead nuts on the money when we checked them right before final assembly......

Machine shop quality seems to be a roll of the dice today. There is a large shop near me, but their reputation is not good and if you have a rare block, look out. In these days of poor employee work/ training, service and narcissistic attitudes at an all-time high, many shops can't be trusted. Unless there was some catastrophic event within the engine, I would leave it alone as Cliff mentioned. Check everything of course and go from there. Poor machining work can really create more headaches than you had before.

[65 Lamnas]

Thanks for all the pertinent info, guys. I used to live in IA but am in IL now, between Joliet and Bloomington-Normal (yes, Pontiac, no joke).....I'm getting ready to start on an engine project for my latest Lamnas, which I'm picking up in a couple weeks.

I think I'll start a machine shop thread