Technical Decking an engine block

I got to thinking , again , after reading a post where a guy is decking his block a few thousands, an FE in this case.
In all the engines I ever built, I cannot remember ever milling the deck on any engine! Mostly because I had no way of really checking it to be square with the crank. Also none of my local machine shops at that time had the capacity to mill the head surface a block.
Over the years I have built many engines, maybe a hundred or so, some just get you down the road, some heavy duty working engines ,some winning racing engines.

What are the thoughts here on the HAMB to milling the deck on engines.






Bones

 

Machine shops that have invested money in the tooling to square a block, can get the block square. And as you've noticed, not doing so doesn't seem to cause problems in most applications.

 

I started hanging around machine shops and racecar shops 45 years ago with my dad. Our local shops all had the capability to deck and line bore blocks.

 

I like to have them machined to 0 the deck to the pistons.

 

I have built quite a few with the decks milled. It is common to zero deck one if you are squeezing the last morsel out of it. It runs right up there with align boring. it gives you two advantages. makes it easier to set your quench and squares the decks with the crank.

I think it is not your normal backyard modification. Most engines come from the factory close enough for a daily hot rod. If you are just screwing one together for a general overhaul the way it came will be fine.

 

Same as Beaner, I had blocks decked mostly for tight quench/squish...And you need to make sure all the rods are exactly the same length..
A GMC 302 I built had the deck tilted to the back and one side, the rod center to center varied by .007...The shop made custom offset bushings made for the rods and squared up the block

 

I know from the factory 460 Fords can have as much as .015 or more from front to back, which is acceptable for factory tollarences. So, yes for a performance build a comptitant machine shop should be able to square up your block and also 0 deck it according to your stack height if you wanted.

 

When I was using 400 SBC blocks in the race car, I always had the deck surfaced. When you were running them hard, they had the tendency to have head gasket leaks between the center cylinders that were siamesed. While I never blew a head gasket, I did see evidence of some leakage in that area when I tore the engines down.

The machine shop that did my 401 nailhead block did a light cut on the deck. I'm pretty sure he also did this on my 312. After all the heat cycles on blocks that are over 40 years old, not everything is as true as it once was.

 

I’ve had all mine decked one so much the intake needed work. Great fix a problem but bad to fit other parts..

 

A lot of the time, perhaps most of the time, you have to float the pistons (bush the rods). Sometimes you get lucky. I pulled an Olds motor down once for inspection/freshening. It came out of a willys coupe that someone had wadded up in the early '60s. the slugs came up even with the decks. The rods were bushed and they had actually drilled oil holes from the big end to the bushings. Off topic for the thread i know but it was freakin cool.

My 355 is running pinks. We got lucky and they were all within about 3 tenths. More than close enough, and totally unheard of for factory rods.

 

All my performance engines get squared in fact I can only remember one that was bored that didn't get decked, back in the 80s I rebuilt the 360 in my shop truck.

 

good way to help fool others as to what you have with ID numbers on right front of block get eliminated

 

Actually in a decent machine shop the numbers get put back on after decking. At least any shop I ever worked at put the numbers back on.

 

The last 4 GMC blocks I built were decked for various reasons ...
One was Korean war US Army 302 - after doing 3 302 Army heads which had been screwed up in numerous ways, I thought it best to deck the block for peace of mind.
One was a 270 that had been hot enough to warp the head .015'', so that block got decked.
A third engine was brought in by a $$$ guy who said "make it as close to brand new as you can."
The last was my '54 248 which had some surface pitting from poor storage that needed to be cleaned up. None of them needed more than .002 - .003 to clean ....

 

True that Beaner but I have never seen a shop replicate the GM factory broach marks in the original decking process. They were wide sweeping arcs probably because of the speed the machines were performing that task on virgin iron. When you are going for big money in the snob-eat-snob 1st gen camaro world, out comes the magnifying glass to inspect the deck. For that reason I try to avoid decking expensive chevy engines for a resto ride. For a performance car, shave away! That's why I refer T/A's, Pontiacs have the ID numbers are the right front cover boss.

 

The person that I learned the most about building engines from taught me to "always check the block for straight & square before you do any thing else : you can't build it correctly if it isn't right to start with, as it is the basis of your engine. It's like trying to build a house with the foundation out of square & not level : sure, you can shim to correct it, but why not do it the right way to begin with?" He had me measure from the crank centerline to the deck surface on both ends of the block, (& on both banks on a V-8) to make sure the crank was parallel to the deck (on both sides on a V-8), then to use a straight edge to check for warp on the deck(just like we check on heads), & (on V-8s) use a framing square to determine that the decks were at 90 degrees to each other. On a stock rebuild this level of care probably isn't really necessary, but it does make for an engine that tends to last longer, & with less problems.

 

The only one I ever had decked is a 263 Buick Straight 8. I had the shop cut .02 off the deck and .02 off the head. It was the cheaper option than custom pistons to get the compression where I wanted it. I did have to do a small bit of trimming to clearance the pistons where the boss for the spark plugs hangs into the combustion chamber.

 

Odds are if a shop can surface a head the same machine can do a block. Not a matter of can't, matter of effort.

 

Hey Billy ,
You are right about the markings,,,,,,it was done with a broach,,,,,at least Mopar was .
Machine shops use a mill,,,totally different marks .

Tommy

 

Well, that kinda depends on the machine shop. My go to machine shop , back forty years ago, when I did most of my building , did not have those capabilities.
In my shop back then I always kept a 350 Chevy rebuilt/ overhauled ready to go. Some needed a lot, some didn’t need much. But I never decked one! Lol!
I never had any complaints!
The deck was what they lined up the boring bar on!
New, modern machine shops seem to have more equipment, than back in the old days…..or at least around my area. Of course the majority of my engines went into just passenger cars or trucks! Around 1979 I built some winning circle track 350s…….and I am a Ford guy!




Bones

 

We always do the decks square to the crank centerline. Factory tolerances are always off maybe by not to much but decking is just part of the blueprinting that makes a difference where it counts.
Ronnieroadster

 

Lately, with fuel being what it is today.............I think having an accurate quench area has become more important. Bought a Chevy core a couple months ago and the guy was telling me he had rebuilt the engine in his 51 Chevy Hot Rod V8 to use in a roundy round. Then he quit racing and put it in his street driver. Didn't have real high compression, but he had to add some octane booster with every tankful to keep it from knocking. I asked him about his quench and saw a puzzeled look.

I think a good way to check what someone has is to take one piston and rod assy and install it in each corner of the engine. Bring it to TDC and use a depth mic (or a dial caliper) and see what it reads from the deck to the top of the piston. Leave the rings on it to help square it. You can probably check a couple places if you think the piston might be cocked. Anyway, by using only one piston you should be able to get an accurate measurement and judge whether your deck is parallel to the crank.

Second, you should also be able to calculate what your quench is by comparing the pin height of your old and new pistons.......if you are using the same rods again. Unless you change rod length, there should be little variation even with new rods. At any rate, this gives you an opportunity to set the correct deck height/quench when building an engine.

Personally, I would ONLY use a machine shop that locates off the main bores when decking an engine. Now the guy doing a cheap bearing and rering isn't going to do any of this stuff, and his engine will probably run just fine for awhile.

There are some guys that seem to be able to fix anything with a pair of pliers and a screwdriver. I'm not one of them. I leave a trail of tools everywhere and am always looking for another one like I just had. It takes me as long to clean up as it took to do any job. But when I do get done.....I'm usually happy with what I did.

 

If it's not a performance build I don't worry about it, but if it's a performance build I would want it decked to be square, and so it would give me between .001 to .005 deck clearance. It will raise the compression slightly but the added squish could help with creating a better burn and detonation tolerance. Depends on the cylinder head chamber style and pistons too, a lot of factors weigh into the equation.

 

I had the deck milled on my '22 Dodge Brothers original engine. Head too. Took a total of .125 off, mostly from the head. 1/8th may sound like a lot but on theses oldies that's like taking 1/8" off the top of a 5 gallon bucket! It all helps though. Managed 62.7 mph by GPS on the highway with my '22 DB Screenside.

Dave

 

I have decked blocks in my bridgeport. Even going going so far as doing it with crank rods and pistons installed no rings lots of grease on the pistons with a degree wheel. measure to find the lowest piston and cut the deck that amount turning each piston to the top when the cutter is there. you get a zero deck engine . Use .040 head gaskets. You do get to reclean every thing.

 

Even a "mundane" rebuild can require milling the deck. Nailhead Buick cast pistons being sold today have a lower compression height, and if you use composite head gaskets instead of the original style steel ones, the deck needs to be milled to have a decent CR.

 

The shop I used decked my 355 just to clean it up and make sure it was square. It was part of the package they sold me, he does a ton of race engines for cars and boats. Mine is .022 in the hole, which is fine for me.

 

Unless they are using one of these


Mike

 

that's a rotary broach, Chevy block decks have a straight line finish on them.

 

The shop I use has big heavy block they bolt to the engine, it's precision ground to match the block angles. I believe he aligns it to the crank, then measures off the fixture so the decks end up parallel to the crank and 45 degrees off true level if that makes sense. When done, top of deck to crank center line is even front to back, with that, any differences in piston hight comes from rod and piston differences.