Technical Decking an engine block

I guess somebody is wrong here.
I know where you can go to get "Wide sweeping arcs", anyhow.
The trick to setting up a big rotary broach is getting all of the cutters ground to the same height. You can tell when it's right from across the room by the "song" it plays. A tall one will leave it's mark, and play a different note . Mike

https://www.accurate-machine.com/
http://www.accuratepower.com/Machine/

 

In the hole measurements are taken in line with the wrist pin. The way that is being measured in the picture, 90 degrees from the wrist pin, at the edge of the bore, allows piston rock to affect the measurement. Piston in the hole measurements must be measured directly above the centerline of the wrist pin. I would re-check this for proper head gasket selection.
If it is really .022" in the hole, for proper quench you only have room for a .015" steel shim gasket to put quench at .037". Recommended quench for SBC is .035-.045". If you happened to be running aluminum heads, you have to use a composite gasket to prevent fretting at the combustion ring in the gasket. The thinnest of these is .026". Which with your.022" in the hole you would be at .048" quench. A little high, but probably OK with aluminum heads.

 

yeah, that's how life is

I've only seen curved machining marks on the decks of Chevys after they've been decked. But I could be wrong.

 

With todays head gaskets is block surface that important?

 

Crank index can also come into play

 

I'd guess no.

Several years ago I took a pair of SBC heads in for some guide work. Father in-law has a valve and seat grinder so all I needed was to have the guides worked on. When I went to pick them up the shop owner suggested I get the heads resurfaced due to them being out X amount (can't remember what amount I was told). I responded with "these came off a good running engine and are going back on the same engine so I don't believe they need to be cut". I declined to have them surfaced.

I plopped the heads back on and never had an issue with head gasket failing to seal. Was the deck surface truly out enough to matter or was the machinist just looking to tack on an extra charge? That I can't answer.

 

I’m not sure what you are saying Mike. The machine tool in post #30 is a Storm-Vulcan resurfacer and it’s a variation of a milling machine. They made some that only did heads and a taller one for heads and blocks. Early ones had high speed steel cutting edges and those would be sharpened when dull, and yes, a cutter or two could be too high. Later machines had carbide inserts that you index for new edges ensuring that all are at the same height.
Chevy blocks (really all GM blocks) BITD were broached, not milled. The block is held stationary and the broaching cutter is mounted on a slide that passes over the deck of the block. Broaches have a series of progressively taller cutting edges that “shave” material as they pass from end to end over the block.
The Storm-Vulcan can never produce the factory broach marks, it uses a rotary cutting action.
Maybe I misunderstood what you were saying but the S-V will never duplicate broach marks.

 

Were they out of spec from being straight or surface? Heads that are low in the middle as small as .003 can cause problems. High in the middle will usually be OK.

 

Actually, it is a Van Norman rotary broach.

Like I have already said, I was responding to "wide sweeping arcs". Made with a rotary broach. Like the one in the picture. Mike

 

Back in the day , when I was building most of my engines, the machine shop I used the most only had a machine that had a long flat table with a grinding stone in the center of it. Pete would just “ slide” the heads back and forth on the table, over the grinding stone. Gave a great surface! I always wondered how “ straight “ they were, but never had any trouble with them! Obviously he couldn’t do an engine block that way!

And he bored blocks , based off the deck! At that time, in my town, there were no machines that bored based off the center line of the crank.






Bones

 

Used one just like it at Garnett auto supply Wichita Ks.

 

I do not remember him specifying where they were allegedly out or by how much. Since I wasn't going to be using steel shim head gaskets and since the engine had no previous head gasket issues, I just assumed I was being sold a service I really didn't need. They may have been out of spec but I still felt I would be fine and I turned out I was correct.

 

It turns out that engines will work pretty damn well, being out of spec in most ways....

If you ever want a really good lesson in what an engine can survive with, overhaul a model T engine.

 

The broach for a block deck is extremely long,,,,,,and has many sections of tooling assembled on the fixture .
The tooling is set on the desired deck angle ,,,and cuts both decks at once .

How accurate the total flatness,, end to end ,,can be a combination of tolerance stack up .
Because,,,,,the mains must be dead on accurate,,,,to locate the decks correctly for cutting .

As the broach goes through it’s travel,,,,,it is shaving a few thousandths at a time .
From raw surface iron from the mold,,,,,to a finished machined deck .
However,,,,,,it can still be out,,,,end to end,,,,side to side even .
The broach is only as accurate as the setup ,,,and the tooling .
These large tooling sections become dull,,,,,and must be sharpened,,,,,then they must be correctly shimmed into position each time .
And each of these sections can become out of tolerance by being angled from front to back .
One section to another even .
And the factory had an allowance of tolerance in these machine operations,,,,,you know ,,an allowable spec . ,,before correction .

A good broach man was an extremely talented worker back then,,,,even now I guess,,,I don’t
know how they do it now .
It always amazed me how they could cut an iron piece ,,as accurate,, as fast as they did .

Tommy

 

I think the 350 Chevy is that way! Back when I kept one or two in my shop for sale, I had various conditions and prices! Some bored some reringed.
Some times I would have a guy bring one in and want it “ fixed” as cheap as possible! Clean and lap the valves, reuse the bearings, new rings and gaskets! Suckers would run great!
Here on the HAMB we tend to build to perfection and rightly should, as it is our hobby! But some of the short cuts that were done , back in the day, just to get a vehicle down the road a few more miles would simply amaze most people!
It is odd that me being a Ford man , I have built twice as many 350 Chevies and all other engines combined! ……and still have never decked one! Lol








Bones

 

Sorry. Still figuring things out.
I have a friend that has a early low HP Fuelie C2.
Ya know how some Vette guys are. He found someone in Michigan I think that has one of the old factory broaches for blocks. Friend went so far as to get his decked for the sake of having it 'factory'
Even got the ok from the Vette judges at Bloomington??

 

Here is a Storm-Vulcan 85B, it can be used to surface blocks, heads and I guess even intake and exhaust manifolds with the proper tooling. I’ve known these machines as Storm-Vulcans for 50+ years, but it’s possible Van Norman bought them out. While I cannot see the name clearly on the machine in your photo it sure looks like S-V to me.
And no matter what Van Norman might describe as a rotary broach the one pictured here sure looks like a variation of a milling machine to me. The cutter is below the ways and the machine operates like an upside down vertical mill.

 

I worked at a machine shop for a little while, about 20 years ago. We had a surfacing machine (mill) that could handle blocks as well as heads. And had a jig to set it up to deck a block based on the location of the mains and cam bore. I did several 350s, they were all out to lunch...and I did one ford, it was only off a couple thou. I was impressed both with Fords machining, and also how far off the Chevys could be and still work.

 

Later in my career, I switched to my friends machine shop after he went out on his own! I think he was about as good a machinist as there was in this area.
One thing he told me about Chevy crankshafts we’re they had a tendency to be off! Not in diameter, but the index as to the throws in relation to each other.
The OEMs had tolaerances and I guess they were quite large.
I always though that maybe that one engine , that everyone had “ one “ of ,that just seemed to run great, was an engine that had closer tolaerances than the average engine! Maybe?








Bones

 

First engine I ever built High tech oiling system

 

Oldsmobile rockets being machined, skip forward to the 15 minute mark. Looks like rotary tools were used on these.

 

Pav ,
Sorry,,,,but an actual factory broach to do production blocks is enormous .
Probably 50 feet long or better .
These machines did it all,,,,,,load and index the block correctly,,,,,then a massive cut that took maybe 20 seconds to complete .
One lick,,,it was done ,,,,,,,that’s what production work is like,,,,,,otherwise they couldn’t afford to build the engines .

He might have had another type of broach,,,,or at least what some call a broach .
Actually,,,,,most are mills,,,,or rotary mills,,,,not a true broach .

Until people get into the automotive world,,,,,OEM,,,,,it’s really hard to imagine how quickly some things can be done .
But,,,, because of the volume of production,,,,,they can afford the enormous overhead and all the setup time .
It can possibly take hours to set up a machine,,,,that is huge money in a factory .
That is why they usually have multiple tools,,,,,duplicates,,,of the same tooling .
You can literally swap tooling and be running again in 5 minutes.
Massive capital involved,,,,but it equals huge returns .

Tommy

 

I think that today most manufacturers realize that the crankshaft bore of an engine is the starting point from which all other dimensions should be held. BUT............backing up from that point, a cast block is after all a raw casting with variations in it. Having machined raw castings as an apprentice and a machinist, I can tell you that they often varied greatly. Lots have been done to increase the accuracy of castings thru the years. If you remember, the nice little all aluminum Buick/Olds/Pontiac 215 suffered so badly from casting accuracy (liner placement) that a large % of the engines were scrapped and the mfg rights were sold to Rover who improved the process. Thes Chevys and Olds were manufactured about the same time so one can expect that they suffered somewhat as well. Being cast iron they didn't have the liner problem but still some engines were known to have thinner walls on one side. Its also well known that the angle of the V was not always perfect and the decks were not always parallel to the crank. The point here is that you start with a rough casting which itself must be reasonably accurately located in order to begin machining. "To put the crankshaft main bores in place", so to speak.

So the starting point for all the initial machining is a casting with variations that affect its initial location for beginning that machining.

As I said, casting processes have improved.....but also machining processes have improved. Now the CNC process often holds the block on ONE fixture for the bulk of the machining. Not having to move thru multiple set ups and holding fixtures gives a better chance for every dimension to be correct and correct to other dimensions and planes.

The vast majority of automotive machine shops out there are using dated/prehistoric machinery. When you are doing one off set ups, this can work very well............if you have a skilled/talented machinist operating the machines. Lots of excellent work can/is done by automotive machinists in small shops using these well designed (but old) machines. Lets face it, the results obtained are usually excellent if the person doing the work is motivated to do good work.

As for whether its better to have a broached finish or a milled finish. There are certain head gaskets today that need more attention in high performance set ups. The other 99% won't really make a difference as long as the machining is done properly.

 

Remember reading one of Hot Rod magazine 400 sbc budget builds that number 8 piston TDC was .060 down in the hole while the front number 2 was about .020
They were disappointed in the power it put out but it would have been interesting to see how much power loss there was by doing back to back dynos after 0 decking.

 

BHJ Blok-Tru

Yeah it'll run, but you're costing yourself power and longevity if you're not squaring up the block.

http://www.bhjproducts.com/bhj_content/products/blueprintfixt/bt1_intro.php

 

For me it depends on the purpose of what I'm doing. If I'm building an engine for myself, it's a cost is no object deal, to a point. The block is going to be made sure the crank centerline is straight and the decks zero'd as well. I may not put the absolute best parts in it, but the best I can afford.

Now on the other hand, we've thrown a lot of junk together for my son. He's young and hard on stuff. He can break stuff more than anybody I've known. Being that he's young, he doesn't have the cash to put good parts into stuff every time. We've done a lot of cam/head/rering deals for him and he finds other ways to break them.

Back to the OP, my parts chaser, on O/T Bumpside Ford has a turd 360 in it. I redid the stock heads a couple of years ago. I'm avoiding doing the bottom end because I know I'll do it right and have it all squared up if needed and drop a 428 crank in it to make it a 410 with appropriate rods and pistons. It runs reliably right now even though it's down on power, so I save the money and leave it alone.

Devin

 

It probably wasn’t the deck! It was probably a poor indexexed crank!






Bones

 

Or both.