I have an SBC block that I am going to take to the machine shop for decking. I have built a lot of SBCs without measuring the deck height. I always just took it to a machine shop with a cnc machine. It somehow measures the deck height. I just tell him I want a 9.00" deck height. And that's what I get. But I am interested in how deck height is measured in a home shop. I know it is center of crank to top of deck. Without a crank in the block, I tried measuring this with a dial indicator. It was really unhandy trying to get the caliper in the crank main bore and hit the deck with a straight shot. I never did get a measurement that I would trust. Short of a solid bar or tube machined to main journal diameter, does anybody have a good method for measuring deck height?
Yeah, that's what I tried to use. I just never could get a measurement that I trusted to take to a machinist and tell him to take .XXX amount off. As I said I don't really have to measure this, the machine shop will take care of it. I'm just interested. I enjoy measuring everything that needs measured before putting an engine together. Especially things that come back from the machine shop. I have all the necessary tools for measuring everything else but have never been able to verify this particular dimension. I know I can pretty much verify the deck job by putting pistons in all 4 corners and checking. But that is not quite the same due to piston rod stack-up variations, as knowing by direct measurement. I'll give the caliper another try, but I'm starting to wonder if I could measure from the rod journal at TDC and do a little math to come up with deck height? Add half the rod journal and half the stroke?
For something that I really care about I will have it bored and take it home to mock it up. I will install the crank and install a piston and rod****embly at each corner , at that point I will measure the piston to deck height at 4 corners.
Even if you trust the machine shop, you may want to verify their work. You can install a single piston in each corner of the block to compare variation of deck height if you are careful. Another way to get exact readings is with a height guage and a set of gage blocks........or better yer a height gage and a Cadillac gage. You aren't likely to find a Cadillac gage easily/cheaply. It is simply a vertical column with a surface every inch. You turn the top of it and it raises and lowers the gage surface so basically it is an adjustable set of gage blocks. Gage blocks are sometimes called Jo blocks......short for Johanson. They are simple precision ground blocks in various sizes that you set on top of each other until you have the dimension you want. That dimension would be the actual deck height. (minus half of the mainbearing hole diameter) (more on that in a second) You remove the head locating dowels from the block. Then take a sanding block and lightly remove and debris or pulled thread on the deck surface to insure its clean and flat. Flip the block over and set it on a smooth flat surface. With the block sitting on the deck surface, you take the height gage with a small dial indicator installed...........and insert it into the main bearing bore till you find the lowest point. Then stack your gage blocks to the dimension that is the same as the reading you got in the main bearing bore. NOW, add that 1/2 of the main bearing diameter to the gage block reading and you have your deck height. Repeat at each corner of the block. That will give you a very accurate measurement. Gage block sets can be found on line for $100 or less, but you will also see them for a lot more than that. You want a set that has a lot of blocks in it in order to make the right combinations. There are some real basic sets that only have a few blocks. The gage blocks are also handy for checking any outside micrometer and even inside micrometers to see if they are still accurate . Micrometers go out of calibration and can be adjusted. Gage blocks never go out of calibration or change size. Anyway, these tools can be used in other ways and are a nice addition to any tool collection. Need this kind of indicator and the brackets to mount it Simply invert the block so it sits on the deck and use the height gage and indicator to find the low point of the main bore. Then build a set of precision gage blocks till you get the stack to give you the same indicator reading. Add half the bore diameter to it and thats your deck height.
I have an 18" electronic height stand that's accurate too within 5 tenths (.0005") which I use at work...
I watched a few videos on decking and squaring a block. Although it wasn’t shown (it had to be though) a bar was bolted to the mains. Long gauge inserted in the cylinder at the corner holes. I****ume the bar was the same diameter as crank journals. Probably overkill for at-home use. Why @ekimneirbo says about a piston****embly moved to 4 corners would get you pretty darn close on squareness for sure. Edit: I suppose if you did the math on the piston rod****embly it would get you the actual deck height as well.
My dad would do the same thing, only he would use the SAME rod, piston, and bearing****embly on each corner for taking measurements. I rolled my eyes at him at the time, but later on it made sense...
One doesn't. But I would expect the stroke tolerance to be measured in the magnitude of a few ten thousandths of an inch. I also know that I can install 4 piston/rods in the corners and check the down in the hole measurement, then put different piston/rod combinations from the same set back in the 4 corners and come up with measurements that can be .001- .002" different due to rod length/piston pin height stack up. I'm thinking that if I measure from the rod journal up, my measurement is only subject to the few ten thousandths of stroke variation. I think that .0001 measurements are important when doing the rod and main bearing clearances, but I 'm not too concerned about a deck measurement being accurate to the ten thousandth.
I absolutely agree with this! As I said above, due to rod length and wrist pin placement in the piston machining tolerances no 2 piston/ rod combos are exactly the same. I have played Tetris with rods and pistons trying to achieve the same in the hole measurements. I've gotten it closer, but I don't believe I have ever put an engine together where all the in the hole measurements were the same. Sometimes it will make you scratch your head and swear that the decks aren't square. The same piston in all 4 holes is the best way to check. EDIT: In case you haven't noticed I am a little***** about precise measurements.
Yes to the above !!! Asking for a specific number...UNLESS...you've ACTUALLY measured with a piston and rod, is asking for trouble, OR, not getting what you THINK...you want ! 1 - Put tape on the piston skirt so it will fit into the bores snugly, and NOT rock at all. 2 - As above, you NEED to use "one" piston/rod combination. Put into each corner bore (all four). 3 - With a "depth" micrometer (a real measuring tool, NOT a caliper !!), measure what you have NOW...for the deck height (in that bore). 4 - Put the SAME piston/rod into all four corners of the block and do the EXACT...same thing. NOW...you have starting point from which you can start the machining process to correct the block. NOW, and ONLY NOW...do you have a starting point ! You MAY find that the block is twisted or off, with two, bore different than the other two measured heights. They "could" be all the same...ideal ! The current "deck height" may be, .010", it may be .005", in many early engines, it could be even .025" (piston in the bore). So now.., you pick a number, usually small or even a .000" (or zero deck) dimension that you tell the machine shop you want. Again, JUST PICKING A NUMBER OUT OF THE AIR IS COMPLETELY INCORRECT, and can get you in trouble ! Mike
If your going for zero deck height, check all 8 rod/piston combinations in one hole to find the longest one, then you would be safe to get a deck cut measure.
I am in total agreement. This method will get you there. But I would still like to be able to get a good direct measurement that I can trust to be able to intelligently inform the machinist and be able to check his work after the fact. Like I said the 4-corner method will get you there. On the engine blueprinting form that I always use when I build an engine, I always record the in-the-hole numbers for each cylinder. It also has a line item for "deck height". I'd like to be able to fill that line. I'm thinking of taking a 2-1/2" schedule 40 pipe (2.875" diameter), I can turn it down to 2.641 (sbc main bore diameter) and still have enough wall thickness. It would only need to be long enough to reach between 2 main bearing bores. My son has a lathe at work available to him that would do the job. Cheap enough to do a mock crank. I think it would be pretty handy to have in the toolbox.
Yes, if done correctly it would serve as a "standard" and you could get the deck height. You would however have to have a way to measure the bore of the rod accurately and the distance to the piston top so you know what the length is. You are exactly right. In many cases people think they can measure accurately in .0001 (tenth of a thousandth) measurement. They can do it if they have the proper tools........but from experience I can tell you that when someone works to tenths, there will be variation. Yes there are expensive machines and inspection tools that can hold tolerances that close and closer.......but what most of us have available to us just allows us to get "in the neighborhood". What I mean by that is if we mic something and the mic or gage reads 2.0025............we may not really be 2.0025 but we are working with such a miniscule tolerance that if we are off by .0001 in either direction..........its gonna be fine. Back when I ran a cylindrical grinder or a hone at work, even though we had micrometers that were graduated in .0001 increments.......we didn't use them on production runs. We had what was called an air gage. A certified standard was placed in a hole and air pressure adjusted till the gage read zero. Then we insered each finished part into it after grinding. It was more accurate. There is always some variation, seldom is anything perfect. So you have to know when you need to work within tenths of a thousandth and when you only need to work in thousandths. Don't think that you are going to get perfect readings and every measurement is going to be "perfect". They aren't, but you should be "in the neighborhood" by an acceptable variance. On deck height I would hope for less than .005 variation and hopefully .003 or less. If you get that, you have done well. ALL machined parts have tolerances.
My hunch is****uming all the strokes on a pre 2000 OEM crank are within "a few ten thousandths of an inch" might end in disappointment. Maybe modern ones come closer. Others with modern era experiences surely know better. Any reground crank would be suspect. Another case where the more I measure my sh*t today, the less ignorant I'll feel tomorrow.
You may very well be right about older cranks not having consistent stroke. I wouldn't know how to measure crank stroke independently of the block. But after measuring half a dozen new aftermarket cranks and the rod and main journals being within just a couple of tenths, makes me think the stroke is probably that close also. As far as feeling ignorant, I think it is more a matter of wanting to get everything right on a new $5-6-7-8000 or more build. I guess it depends how lucky you feel! Me, I want to hit that start*****on with all the confidence I can muster. I know I could throw an engine together without measuring a thing and have done so when I was a kid. They always ran, and sometimes they ran but didn't last very long. Now I like to be a little more careful.
Stroke length on crankshafts is usually pretty consistant on OEM crankshafts, but its not really important that all journals be within tenths of a thousandth of each other. Thats one of those dimensions that is not necessary to get that close. Its basically a non-factor. They may actually be that close or they might be .001/.002 different and it won't make any real difference. The diameter of the crank journals however is critical that it be within tenths of a thousandth........and with the grinding equipment that is used.......thats reasonably easy to do. Thats what I was referring to when I mentioned above that you need to know "when" you need which degree of tolerance. Off the top of my head, I'd say the most precise need in an engine is between the wristpin and the piston.
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