Technical Squaring a block vs decking a block

Is there a cost difference? Rough ideas between the two, or is it “hey, we just spend a few more minutes”?
Thanks

PS. No shop opened today/tomorrow to ask.

 

If just decking, they may just take a cut off the deck not knowing if deck surface is square to crank or not. Squaring, would need to check each corner bore, by taking ONE rod and piston combination and measured deck height in each corner bore. If all corner holes have same deck height, safe to say the decks are parallel, or square to crank.

 

might depend on what equipment the shop has...where I worked years ago, we could machine the deck relative to the crank/cam bores. It did cost a bit more for this setup, than a normal deck resurfacing based off the existing surface

 

My machine shop checks all 4 corners relative to the crank before cutting.

 

Decking = cutting the area flat. HOW they are setting up that cut could be many things.
Squaring = cutting the area flat and true to the crankshaft centerline.
First could be second, but second is more particular.

 

You would be amazed at how far off some factory engines are.....

 

I noticed that chevy 350s were invariably way out of square...over 10 thou usually...Ford were not so bad

 

Wow, I wouldn't have guessed that much...

 

The most often used is the BHJ Blok-Tru square deck fixture. It positions the block off the crank main bores and cam bores. When done this way, the finished block has both decks the same height and at 90-degrees to each other.




And yes, many older V8s are way off; Chevys are usually the worst.

jack vines

 

I would have thought decking would square the block as well.
So I guess I should ask them to square and deck the block?

 

You should ask what they have to offer and see if it meets your criteria and budget.
There are a ton of videos describing automotive machining and "blueprinting".
If all you need is a basic rebuild, you don't need anything but the warranty and what's needed to meet the requirements in case it fails.
If you want good reliable power say for bracket racing or fairly open road racing, you will need some things done for longevity and supporting the additional power. This can range widely, but this area applies to most street cars and amateur racing.
If you are going for bleeding edge power within the rules to place in a race, you need to understand the limits, discuss each spec and be right up against it, and also try to get as little HP loss as possible from each part. This is where some or all of your competitors may read the rules carefully and consider everything not exactly prohibited as basis for the build.

 

Nothing extreme here. But, I had a plan. Unfortunately I have to change my plans and somewhat “back yard” this engine.
But in order to do this, deck needs to be lowered, or heads shaved.
I’d prefer the deck be done and squared.

 

See in red above !
In most "modern" shops, when the block is setup in the machine, the main saddles in the block are the MAIN feature that all machining is done off of.
So when the block is "decked, it's ALSO..."squared", and visa-versa !

Mike

 

Good!
Just remember, tolerances can stack up. You said heads. Here that usually means V something, not a big straight diesel.
When the deck is cut (or the heads shaved), the head to intake mating surface changes. Small amounts usually still bolt up. Big changes will require checking and possible further machining. The heads moving closer together can move the intake bolt holes or the intake cut and/or need the china walls to be cut.
Check head bolt length, too.

 

So, this should actually go back to factory. The engine used a .022-.026 (I forget) compressed head gasket. If it decked and I use a .041 compressed gasket, she’ll be close so no alignment issue occur.

 

Once the deck is cut and square to your liking, I would check how far down in the hole the pistons are. That may determine which head gasket thickness you choose to have correct quench.

 

Thanks, @big duece . I was going to ask what the deck height was, what cut was needed, what the crankshaft throw was, rod length, piston compression height and if the heads have been also checked.
Stuff gets complicated when there is so much all at a single surface! Haven't even asked if the cam/valve lift is the same!

 

@RodStRace has the info and why, but it’s a 1 pc RMS 350 that my plans changed from “doing it right” to “getting it done “.

 

PM replied!

 

Some rebuilder pistons may have a lower compression height assuming your deck is being cut. If you have the deck cut with a "0" deck height, you would run a .040-.045 gasket to get that same distance for quench. I would rather see having a deck cut just the clean and square it up. If you cut it strait to 0 deck height right away, no room to do further work.

 

Yes, pistons I’m looking at have 1.56? Not 1.54 pin height.

 

I also want to throw this out there. Don't assume the casting is all meat. It is a good idea to sonic check bores on an engine when you are going to sink dough in it on machining. Head and deck surfaces can get unnesarily thin and cause big problems. If this is an engine for the street you may be throwing money away on stuff you won't be able to appreciate. All this stuff can be measured prior and guide you to consider finding a better block. I am all for starting with good foundation. Everthing lining up and at correct angles is the first step to building horsepower.

 

When working on a Pontiac 455, I measured very carefully every cylinder using the same piston and rod in each hole to see how far off the deck was end to end and top to bottom. I wrote each measurement down and took the block to my machinist. It was slightly tapered front to back and each deck was slightly tilted. He used a fixture like the one shown above to cut each deck square to the crank. The decks were level, and true 90 degrees from each other. When I mocked up the engine again to check piston hight, I found them all still slightly at different heights. The factory crank turned out to be not 100% right as far as rod journal distances from the center of crank. By swapping rods and pistons around the block I was able to even out the small discrepancy's and get a pretty even deck hight.

 

Just ask the machine shop whether they locate the block off the main bearings when decking? If they don't, then use a different shop. While the quality of the work being done can often be controlled by a good machinist without the best equipment, as a machinist I will tell you that having the proper equipment makes the work easier and faster to perform. Time is money.......... You usually get better results from shops that have the right (not necessarily the newest) equipment.

 

Using the fixture shown above that indexes from both the crank and cam centerlines might offer one other slight advantage. It would also ensure that not only would both decks be 90° apart, but that each deck would also be 45° from the centerline between the crank and camshaft. That seems like really splitting hairs, though I imagine it could have some very slight effect on camshaft timing from side to side.

Or maybe I'm just seriously overthinking things here.

 

I always wondered how accurately the cam bore was located in blocks...???

 

For true. Many older factory cranks were not perfectly indexed and on stroke. In theory, when regrinding a crankshaft undersize, if the guy operating the crank grinder wants to take the time, he can get the crank with all the throws the same degrees apart and the strokes the same length. The reality is it takes too long and too many cranks would go junk or at the least end up .030" under. It's always more cost-effective to just live with the slight variances.

FWIW, we hamburgers don't always want to accept it, but because of CNC, any of today's economy car engines are more precisely built than the best blueprinted race engine from back in the day.

jack vines, who was there back in the day

 

My shop in McMinnville uses a CNC machine,,,they load it like Jacks pic .
Then the machine turns it 90 degrees one way and uses an electronic probe to measure the deck surface,,,,,several areas on the deck .
Then back to center,,,and 90 degrees the other way,,,,,again using the probe .
Then they now the exact deck height and how much to cut from each surface .
Not cheap,,,,,but very precise .

Modern technology,,,,,like Jack said,,,,most modern factory stuff is almost dead on .

Tommy

 

Where do y'all find machine shops that still do this kind of work?

 

We still do it every day. The easy, affordable part is square-decking the block. The expensive PITA is when the customer wants the piston to be in an exact relationship to the deck. That requires assembling the crank, rods, pistons, measuring everything, calculating the required deck height, disassembling everything and cutting exactly that. Speed costs money; how fast can you afford to go?

jack vines