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Measurement, Instruments and Metrology

A recent thread about rolling-your-own rod bolt stretch gauge got me thinking about the practicalities of measuring various engine components on teardown. It seems to me that what is needed is a thread describing the various tools required to measure engine parts-- and how to use them.

Where I grew up you couldn't swing a dead cat without hitting a tool-and-die maker or an aircraft mechanic. As a result there was no shortage of competent, experienced people who could give you some experienced, curmudgeon-like "old guy" advice on measurement and machining, albeit in "thou." THEY learned it in Shop (Called Industrial Arts when I took it) or Trade School or during an apprenticeship. But the sun is setting on America's industrial age, and with it goes our collective experience gained in the days before CAD/CAM.

I am unwilling to accept the line "have the parts measured by your machine shop, you can't do a repeatable, accurate job yourself" anymore than I would accept being told I can't do a corner balance and alignment myself. The only way to learn something is to be taught by an expert and then practice, which is what this thread's all about.

So with the introductory BS out of the way, I'll start. I have the following instruments.

1) Mitutoyo Bore Gauge, 50-100mm measuring range, model 511-453. This is accompanied by a dial indicator, 2109F, which is accurate to 0.01mm. The way this works is you determine, using the caliper, the approximate dimension of what you're measuring, and then attach one of the "anvils" which are carbide-tipped extensions of the instrument, and one or more "washers" which come in .5, 1.0, 2.0 and 3.0mm sizes, until the instrument is approximately the right size for what you're measuring. You then set the gauge to zero using a ring gauge, which is basically a steel doughnut, or a micrometer set to the check dimension. You are supposed to "preload" the gauge by 20 or so to both move the indicator needle to the 12-o-clock position, bring the needle into the indicator's accurate range, and finally, give yourself the flexbility to have the needle swing oversize compared to the check dimension, i.e. less than "zero." Once set, the gauge must be oriented perfectly perpendicular to the bore and multiple measurements taken to verify an accurate reading. At the end, check against the standard to be sure things didn't slip, much like one would take a fifth tire temperature at the track, so you can know how much error was introduced due to temperature change during the process.

2) Digital Vernier Caliper, 0.1 accuracy, for rough measurement. Pretty simple: zero it, slide it, read it.

3) Mahr "Millimess" 1003. This is a comparator-type dial indicator, which means it doesn't measure absolute distance, but relative distance vs. a standard. This is used with a "comparator stand" which is a granite or steel base on which the part being checked rests. You first use gage blocks or a standard to set the gauge to zero at the check dimension, then remove the standard, introduce the part and read the difference.


4) Fowler Micrometers, made in China, four in total, 0-100mm coverage, 0.01mm accuracy. Not the most accurate but didn't break the bank.

Now for the Metrology part. The little white specification books call out the check dimensions for various parts. Here's an example:

Engine Type 2000-- Standard Size Cylinder-- Group 0

Bore Diameter 80.000- 80.010 mm

Piston Diameter 79.935-79.945 mm

Tolerance +/- 0.005mm


Now, remembering high school math, the zeroes to the right of the decimal are significant digits, which means that Porsche is telling us we better be capable of measuring to the thousandth of a millimeter. The Mitutoyo Bore gauge is only accurate to the hundredth of a millimeter, which means the best I can hope for is to nail the second digit, but if I can get it repeatably close to the same measurement, say in 20 trials, that will be enough to tell whether a) It's junk, if it's out of tolerance by 1mm or so or horribly ovaled, tapered or otherwise unusable. An otherwise unscratched, unridged cylinder that measures close to spec would be call for further inspection with a more precise instrument.

The pistons are an interesting case-- there is actually a photograph in the factory shop manual of the skirt being measured on a comparator stand with, you guessed it, a Mahr 1003 Millimess. For these the standard is higher, but according to Mahr, the 1003 is accurate to one Micron, or one millionth of a meter, or 0.001mm. The cylinder to piston clearance permissible is 0.045-0.065mm, so this should provide an accurate check, again using the standards to verify accuracy as you go and performing a high number of trials to make sure you're doing it right. This is where the old pros outshine us punks. . . the ability to make accurate, repeatable measurements rapidly separates the journeyman from the apprentice.

Anyway, you can see where this discussion is headed. Does anyone have their own measurement experiences to share? How about you, Chris Bennett, you've made many thoughtful contributions in the areas of deck height and verifying TDC, is there anything else that stands out? Grady, you posted a picture of a Mitutoyo bore gauge, do you have any tips for getting a repeatable measurment? No less a personage than the Late, Great Harry Pellow himself used to talk about keeping his Bore Gauge in a constant temperature oil bath, do you recommend this?

What equipment do the pros that hang out here use?
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Old 02-04-2007, 10:51 AM
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Not a pro here but what I use for my hobby:

Mitutoyo bore gage
Brown/Sharp outside Mics thru 4"
Lufkin Inside Mics thru 6"
Granite Surface Plate Grade B
Gage Blocks and Pins Grade B
Neway seat cutters
B&D valve grinder
9" Southbend lathe.
Bridgeport Mill

With this equipment I make a lot of the special tools needed for the job at hand, such as valve guide drivers/installers, heigth gages, seal installers, head facing jigs, seat pullers/installers etc, thats what I really have fun doing.
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Old 02-12-2007, 04:28 PM
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I don't have much other than vernier calipers. If something needs a tight measurement I take it to someone with the tools. What I have found though is that for the most part you can tell the wear on an item by looking at it.

For instance if you are looking at your pistons you can see the original machining lines and you can see where they are worn through those lines. Same with cylinders when you look at the hash marks. Cams you can see the step where the rockers follow the cam lobe. Piston clearance you can use a feeler guage. You see where this is going. You don't really need to measure many of these things. A visual inspection and experience can tell you alot about when an item needs to be replaced.

-Andy
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Old 02-12-2007, 05:48 PM
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Jee whiz Craig!

you have a veritable machine shop! 9" Lathe and a bridgeport ain't shade tree equipment

Andy-

for those of us who have no experience and/or want to get experienced we need to measure so we can learn what good looks like... and what bad looks like Trust me, I'd rather spend $ on go-fast parts instead of exotic measuring tools though, there is some satisfaction learning how to use them! Oh, and we can't forget gadget lust!

Best regards,

Michael
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Old 02-12-2007, 06:31 PM
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Re: Measurement, Instruments and Metrology

Quote:
Originally posted by john_cramer
How about you, Chris Bennett, you've made many thoughtful contributions in the areas of deck height and verifying TDC, is there anything else that stands out? Grady, you posted a picture of a Mitutoyo bore gauge, do you have any tips for getting a repeatable measurment? No less a personage than the Late, Great Harry Pellow himself used to talk about keeping his Bore Gauge in a constant temperature oil bath, do you recommend this?

What equipment do the pros that hang out here use?
To my great disappointment, I have not been able to get usable measurement using my bore gauge (a $260 Peacock 2-6") and 6" micrometer (Starrett). I can get repeatable (but wrong) measurements. It's almost like the face of the my micrometer isn't flat. I still use them to check for ovality but I can't use them to get actual inside diameter.
-Chris
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Old 02-13-2007, 03:58 AM
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I work in a machine shop. I have almost all those tools, and used them in my rebuild. I use a good quality micrometer for pistons.

Looking around most engine rebuild shops I realized that their tools are inferior to mine. Of course they mainly do V-8's and anyone can do a V-8.

As for constant temperature? I don't take my car, or myself, that seriously, and it's -20 degrees here today. There is such a thing as overkill.

A bit of applied common sense is frequently more useful than a bunch of expensive tools.
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Old 02-13-2007, 04:29 AM
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This is a great thread. I wish it would have been around a few years ago when I was trying to figure out the best way to use some new tools.

I admit that have spent some time getting to know my measurement tools. I have a nice set of outside mics (Starrett) that I inherited from my grandfather. I also have a cheap set of outside mics and a cheap dial bore gauge. My chinese made outside mics give the same repeatable measurements to 0.0002" as the Starretts, both on measurement standard blocks and other items. I have been pleased with this finding and use the cheap ones more often than the nice ones. does this mean that 2005 manufacturing technology is better than 60's or 70's? I guess so if you are referring to Asian made parts.

My 2-6" dial bore gauge set is a bit different in use since I am unsure of their quality. Here is that I do to measure cylinders. I take the appropirate outside mic and set the dimension to the diameter (usually min wear spec) of the cylinder. I then setup the dial bore gauge to "zero" within the outside mic. Then I place the dial bore gauge in the cylinder. The gauge reads the outside-mic-set, min-spec +/- the true dimension. It makes it really easy to read ovality and wear. btw, I replaced the 0.0005" dial gauge with a 0.0001" dial gauge.
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Old 02-13-2007, 10:08 AM
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Quote:
Originally posted by jpnovak
does this mean that 2005 manufacturing technology is better than 60's or 70's? I guess so if you are referring to Asian made parts.

I think so. Most Chinese precision tools come with certification. That's good, provided you can trust the certification. You should always check a new precision tool before you trust it.

No one mentioned it yet, but a set of gauge blocks is very useful. Like all other things, the Chinese sets are affordable now.
Old 02-13-2007, 10:12 AM
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Quote:
Originally posted by PBH
I think so. Most Chinese precision tools come with certification. That's good, provided you can trust the certification. You should always check a new precision tool before you trust it.

No one mentioned it yet, but a set of gauge blocks is very useful. Like all other things, the Chinese sets are affordable now.
Exactly, how do you know if your mics are correct unless you have a standard to check them with. You can get a nice 81 set of blocks well under a hundred bucks, Grade B Accuracy to +/- 0.0000050" and see what your mics read, I check my calipers and they were off .003 at 3 inches, thatís a lot..
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Old 02-13-2007, 10:39 AM
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And....yes, gauge blocks should be used at the correct temperature, unless you splurge and buy ceramic.
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Old 02-13-2007, 10:43 AM
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Yep, cold means shrinkage, we all know about that donít we?
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Craig, Are you using the KA 1408 Neway set, or did you put it together seperatly?
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Old 02-15-2007, 05:43 AM
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Since I only did 2.7 and 3.2 heads I purchased the cutters seperate, I got the 642 and the 272 which will do both heads along with the 9mm pilot. These give you the 3 angle cuts you want..
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Old 02-15-2007, 05:45 AM
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Retrieving this thread from the discussion of milling!





As you can see I finally got around to measuring my crankshaft. I used a Fowler Micrometer with a resolution of 0.01mm. After setting it up on the standard, I noticed that it was out of calibration, and of course there are no instructions in the box. Fortunately, I recently read two books on the subject, which were:

Inspection and Gaging by Kennedy et al., 1966 edition; and
Fundamentals of Dimensional Metrology by Busch, 1967 edition.

For the type of measurement I'm making, the old editions are fine, and I think I paid $6 for both of them. Anyway, they explain that a micrometer is calibrated by setting it on the standard and using a little wrench, that looks like the fan belt wrench for a 3,2 engine, to turn the barrel that holds the lead screw until the correct reading is shown.

With that out of the way, I made the measurments. And I soon discovered that resolution of 0.01 is no good for measuring cranks, because all the specifications are in 0.001 in the spec book. Also, the two books above said it's important not to round off measurements, even though the index mark may appear exactly in between two marks. Anyway, I just ordered a 50-75mm mic made in the PRC with a resolution of 0.001 and a digital readout, this should help.

Tom1394 mentioned an excellent point which is that instruments at one temperature and parts at another don't make for a reliable measurement. The standard gaging temparature is 20C or 68F, which is what everything is intended to be used at. Without going into the details on expansion coefficients, the act of holding the micrometer in your hand for 15 minutes while you measure crank journals tends to heat it up, spreading the jaws apart, which would tend to make your measurements undersize. Tom's recommendation was to bring the parts and the gages inside and let them heat-soak for 24 hours before making measurements. I would add to that if a surface plate is being used, that should be similarly positioned in advance, as slabs of granite take a long time to heat up or cool down.
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Old 03-28-2007, 05:03 AM
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Anyone else think that .001 mm is bit of overkill ? Since 0.01 mm is only 4 tenths, ie .0004, why do you think you need to go to 0.00004"?

Get your temperature controlled room ready....

The tool you have shown is the correct device to determine the fate of your crank.
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Old 03-28-2007, 05:28 AM
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Measurement tools are getting really inexpensive these days...

0-4" outside mics @ .0001" resolution
2-6" Dial Bore Gage @ .0005" resolution
81 piece Gage block set Grade 'B'

$150 shipped, all new, from Enco (www.use-enco.com). Yes they are made in China. Am I going to use them every day... well no so I think this is just fine. If I bought them as Mitutoyos I could have been pushing $1000... These tools should be fine to check anything I could ever need to on this car... I hope

John, if you held the mic like you show in your pic, yes it gets further apart, but if you hold it at the end it gets closer together If you hold it on the sides, well it doesn't matter then...

Here is a good SHORT tutorial on temperature changes in materials and the effects on measuring:

http://emtoolbox.nist.gov/Temperature/Temperature%20and%20Dimensional%20Measurement.ppt

Based on a source listed in the above ppt, Cast Alloy Steel has between 8.3 and 8.0 10^-6 in./in. / Deg. F change (high strength steel slightly less ~5-7). So if we say the crank is ~8 and the diameter we are using is about ~2.5" and I take my crank from my nice air conditioned home set at 75 to my garage at 85, the diameter will grow by:

8 10^-6 * 2.5 * 10 = 0.0002" or 0.005 mm

This does not take into account the materials disparity on some things... Mag case at 16 vs. tool steel ~7. The ppt states everything is geared for being accurate at 20deg C... Closer you are to that, the more accurate your measurement will be...

For me, well I'll just put everything out and have a beer prior to measuring (I'll be sure to warm up my hands before using my tools)



Best regards,

Michael
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Old 03-28-2007, 06:43 AM
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Don't let'm get to you John. Some of us are just keen on quality tools. Hell, for the amount of money I spend on parts for these motors, I wouldn't use anything less. The Chinese stuff is getting better, but when it comes to determining what I'm going to do with an almost impossible to find part, I'll trust my Mitutoyo every time.
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Old 04-03-2007, 03:41 AM
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Nice John! Last night I put my other dial gage in the bore gage I bought and it fit fine and measured the same, but better resolution, effectively converting my 0.0005 to a 0.0001 bore gage. I bet you could put the Millimess into a bore gage and get pretty accurate readings. You would have to set the bore gage at nominal to start an the total movement would be limited, but I'm pretty sure it will work just fine.

Shbop: BTW, I really like nice tools... and given the funds I would have them, but I make the choice to get the motor running again instead *shrug*
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Old 04-03-2007, 05:29 AM
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I understand. Opportunity costs ae severe with these motors .
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