Technical Squaring a block vs decking a block

Truing/squaring the block should also included checking & resurfacing if needed, the bellhousing flange, so's that it also is perpendicular in both planes to the crank bore. Lots were not all that accurate, esp when tooling got a bit "loose".
Marcus...

 

Yeah, and a CNC is only as good as the operator and the shop. Tools wear, tolerances stack and the jigs and clamps need to be monitored for clean surfaces and proper clamping.

 

We are rapidly loosing machine shops here.

 

I have seen SBC's that were what I would consider way off.

Many had somewhere between 200k to 300k miles on them, and did not have issues but extreme uniform wear.

You'd be surprised how few specs are exact from back in the day.

 

I had a 1965 283 that was .015 out of square on one side

 

I was going to check 4 corners yesterday, but got busy with something else. Should be able to the end of the week.

 

Not all that uncommon.

 

Mike bore it first ,Then dummy assemble the 4 corner pistons and rods [with no rings] and measure the corners at TDC
I did this on my 283 and then I swapped out the 4 pistons with the remaining 4 and measured again [just in case there was a rod length/compression height tolerance]

My block was decked so the pistons were .005" out of the hole. And we used standard .039" Fel-pro 1043 gaskets leaving .034" quench.

You can go a lot higher out of the hole with careful measuring and parts selection

 

Make sure that if you are boring before decking to have it bored with a bar that registers of the crank bores. If your shop has one that registers off of deck, you would have to deck first, then possibly re deck to get piston tops where you want.

 

I’m trying to keep the static CR at 9.4-9.5. I’m checking finances. Been a very expensive past month or so, and my daily is giving me some issues. So need to hold some in reserve.
I need to call the shop when I have time this week get a rough estimate on boring it, honing it and square decking it and balancing the rotating assembly.
I feel I have the crank in pretty good shape, chucked it up in my lathe and polished the journals with 600 or 800 emery cloth with WD as my line, mains with .001 undersized bearings were looking good at pretty close to .002. I never checked the rod journals though.
The thrust bearing was a bit tight, but fit it to .003, I may go a bit more, I know it’s the low end of the spec, so will MMO and 600 grit them down another .001 to be safe.
But it all hinges on what the shop cost they tell me is. It may be a little now, a little later, etc.

Life is fun when that bastard “unexpected Bill” knocks on your door!

 

Its not just "Not uncommon" - its EXPECTED! I don't recall ever having a SBC block on the Blockmaster where both decks were at the same height, unless someone had previously made that correction. 15 thou off is normal, unfortunately. Its also common to find a 5-7 thou dip in the block surface.

 

Be careful when measuring off piston tops to get deck hight, the piston can and will rock in the bore. I measured off the center or along the wrist pin line of the piston. You can also wedge the piston to one side, just be sure to do the same thing for each piston for repeatable measurements.

 

On the now imploded WebRodder site they did a build on a 331 Hemi. When checked the decks wern't square front to back or top to bottom, also the 2 decks wern't equal distance from the center line of the crank.

 

You should be able to simply measure the length of the rod and piston and calculate the needed deck height without assembling the rotating parts. Check all piston pin heights and all rod lengths for accuracy, but these days most of them are pretty close. If they are off, there is no way to get a deck height thats correct for all of them.....but its usually very close. Like you mentioned, assembling and checking is time consuming and expensive. Whoever assembles the finished engine should be the one verifying actual assembled dimensions........

Yes, it should.......thats why its important to locate off the main journals. Look at it like this.........

When a cast part was originally machined while in its raw state, its put into a "holding fixture" for machining. That fixture only has cast surfaces to initially locate the part. Castings vary, so there can be some initial differences in where the holes are put into them. In the distant past, after the initial holes were put in, if the casting looked OK, then there were additional locating fixtures on different machines that used these holes to align the block as it moved from machine to machine. Each machine will then have a tolerance of size/location as it performs its specific operation. One machine may perform an operation that uses all of its tolerance in one direction. The next machine maty perform its operation and use all of its tolerance in the opposite direction. Everything ends up being in tolerance but moving from machine to machine increase the chances of variation.

Today, the casting processes are much more accurate, so there is less variation in making the initial locating holes. Then the blocks are placed on machines that can move in multiple directions at the same time and even tilt and/or rotate the part mounted in it. Instead of moving the casting from machine to machine, virtually all the machining is done at one time on one machine...........so everything is easier to keep in relation to the other features.

Now you take your 40+ year old casting to the small machine shop for machining. Most do not have CNC machines and they must work with older stuff which is still expensive. If you are only needing a block decked, it should be a simple operation to do correctly if that shop has the right tooling to mount the block on the machine with the main bearings. If they don't.........go somewhere else.

We've all seen blocks where the cast cam boss at the front of the block was not centered very well in the casting. The more important dimensional consideration is if its the correct distance above main bearing bores. This location usually has a reasonably close tolerance..........but with CNC today I would expect much more precise even with production tolerances. The thing is, it all starts with trying to accurately locate a raw casting with no precision surface to locate from.

Below is a special tool I made for my Cad engines. While I could use a crankshaft throw to measure, I cobbled this up because I had the stuff on hand and it makes things easy and accurate. There is a larger diameter that sits in the bore. I mount it in the 2 rearmost main bearings. Then all I have to do is take a depth mic and measure down to the larger diameter. It could just as well be a straight shaft tho. I measure the deck on the two rear most cylinders, then install it in the front ones and check the front deck heights.

It also has the ability to check the alignment of the bellhousing at this early stage of "blueprinting" (?). Its easy to check the bellhousing at this time and make any alignment corrections before the engine is completely assembled.

 

With the old factory machining processes, would it be likely that the cam bore centerline would not necessarily be parallel to the centerline of the main bearing bores? Maybe both these boring operations were done with the block in the same fixture to eliminate that problem.

 

Factories have been using CNC in some form since the 60s. They were pretty good back then but used old mylar tapes with holes punched in them. One bad hole and they had to make a whole new tape to correct or change anything. Most of the refinement today is in the ease of programming them.......no mylar tapes for sure.

My guess is that you are correct that they probably machined all holes or features that that are in the same plane at the same time on one machine. Then they moved to another machine and did a different plane. I remember one machine at the weapons facility that operated in 5 planes. X,Y,Z, with a rotating table that could also be tilted . It was a BIG machine and all the axis could be operated in unison with each other, but most machines were more limited in how many planes they could machine with one set up fixture.

 

1963 Olds,
1962 Ford,

It took some pretty big machines to make blocks! Wonder how may the inspector looked at before he could spot defects just by eye balling them?

 

I have bored several inline 71 series detroit diesels for oversize sleeves. Doing these in a horizontal boring mill, what I found was moving from one hole to the next using the factory bore spacing, the original spacing doesn't necessarily match the factory spec. I first thought this might be due to the block being stress relieved over time via heating-cooling cycles during operation, but realized that's likely not the case as the spacing variation was random.

Its possible to determine where the nearest bore center should be based on measurements from the machined surfaces of the main saddle that carries the thrust bearings, and from that center as zero you can sweep each bore with an indicator and have a map of the actual vs theoretical center for each bore. Takes maybe 45 minutes to do the measurements and know where you are before you start cutting. The worst hole center determines how much oversize you need to bore to end up with all the centers where they should be and all the holes the same size since you wouldn't want to have to use different size sleeves for different holes. You actually could do that, but most people would consider that sloppy work.

Anyway, in doing that work, it made me wonder how accurate the bore spacing is on the run of the mill car engine, and if that is something that's normally checked when doing machine work on a block destined for performance use.

 

Before I had machining done on a BBC I was told all of em are "high" on opposite corners after a time due to stresses in operation and production stds. I might be backward cuz it was a while ago (30+yrs) but I think it was high in the pass rear and drivers front. .018 off, and we wanted it down a bit so we took off .024, and yes squared to the crank center line.

 

and that seems to me to be something that won't affect performance at all....

 

Let me try to explain something that may be right or wrong here depending on how you meant what you said. I want people unfamiliar with machining to be sure they understand what you said....or meant to say (?).

They load it like Jack's picture...........I assume you mean they have a similar or the same type of fixture that locates the block by the main bores and the cam bore for centerline and vertical centerline. Thats the best way for any shop to start when machining. Then all machining is done from that "reference" location. The block tilts in the movable (rotatable) fixture to the desired angle and a milling cutter passes across the deck surface front to back (or vice versa). As it makes this pass it will cut the deck surface flat and parallel to the main bores. You can adjust the depth of the cut to take what you want. It will automatically be "square" unless the holding fixture is damaged or worn. Rotating the block 90 degrees (or whatever that type engine needs) from the first cut will pass the "centerline" and end up exactly 45 degrees from vertical on the other deck. Without adjusting the milling cutter, the machinist can then pass over that deck surface and it should be exactly the same height as the first deck and also automatically be square.

Its a really simple operation and the squaring happens as the cuts are made. If piston and rod assemblies are the same length, inserting any of them in a bore should give the same reading on a micrometer.

I would suggest anyone wanting to build an engine purchase an inexpensive digital scale and make a simple holder for balancing their rods, pistons, rings bearings at home. Spend the time to get them balanced closely rather than pay a machine shop. They can only spend so much time matching them or the customer will gripe about the charge, so match them yourself, and then the machine shop only has to balance the crank using the weight you tell them.

If replacing a crank (or using a stroker crank) the lighter the piston and rod assembly.....the easier it is to balance. Many people try to save money by buying a cheaper but heavier rod and piston........then they get bit on the other end when the machine shop has to add expensive Mallory metal to balance the whole assembly. If you are light enough with the pistons and rods, they only have to drill a hole in the crank throw to remove metal....not add metal.

 

This is an interesting tidbit. The beloved flathead V8 ford camshaft is off center. I'd never owned or worked on one when I saw the blueprint for it.
https://www.jalopyjournal.com/forum/threads/flathead-ford-asymmetrical-why.457580/

 

And the cylinders are not on the cl of crank either, by .168. Some engine manufacturers are doing the offset as it changes the piston dwell. Think Ford new that?

 

Seems like there are always exceptions, and I had never heard of this about flatheads. In a case like this or any other uncommon configuretion, its simply a matter of having a mounting fixture thats designed to work with that difference. In this case, the locating pin for the cam journal would have to be offset .0242 to work properly, but rotating the block 45 degrees each way would work the same. Wonder how many of these old engines got machined by someone who didn't know about the offset? That example is why I say its best to go to a machine shop that has the proper tooling............and I also should have said..........experience with the engine being machined.

 

Cloned Hot Rod magazines Junk Yard Jewel vortec head project about 26 years ago with a few more improvements, among them we also bored and 0-decked a 4-bolt main 350 block for the build.
This was the first block the local machinist 0-decked as he had just bought the grinder capable to deck a block, so I was his first customer, he made a short set of head location dowel pins and installed them too the same height as T.D.C. of a piston and rod installed in all 4 corners, he then set up grind to equal the height of the pins.

Used .041 Fel-Pro head gaskets with forged flat top pistons and it's still running strong.

 

After looking at the engine diagram, my suspicion is that they had to move the cylinder downward to make room for the valves between the cylinder and head stud/head sealing area..........and maybe to have better geometry for the valve to cam relationship. But that's just my SWAG......