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.
http://forums.pelicanparts.com/uploa...1170618597.jpg

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?

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.

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

Jee whiz Craig!

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

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

Re: Measurement, Instruments and Metrology
 

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

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.

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.

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, that’s a lot..

And....yes, gauge blocks should be used at the correct temperature, unless you splurge and buy ceramic.

Yep, cold means shrinkage, we all know about that don’t we?:D

Craig, Are you using the KA 1408 Neway set, or did you put it together seperatly?

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..

Retrieving this thread from the discussion of milling!

http://forums.pelicanparts.com/uploa...1174870841.jpg
http://forums.pelicanparts.com/uploa...1174870889.jpg
http://forums.pelicanparts.com/uploa...1174870956.jpg

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.

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.

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)

http://www.pelicanparts.com/support/smileys/pint1.gif

Best regards,

Michael

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.

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*

I understand. Opportunity costs ae severe with these motors .:)

You can always borrow tools. No one is going to lend you new P's & C's.

Yep, that's the Millimess. Here's what I did to measure the valve stems.

The Millimess is a comparator, not a direct-reading instrument. That means that it has to be zeroed with a gage block at exactly the check dimension, then you introduce the part and read the difference from spec. In this case, I used the 9mm gage block from my set of 87 Metric Gage blocks. First you clean all the oil and grease off the block. As this is a brand-new set for me, there was significant cosmoline that I stripped off with rubbing alcohol. The faces of the gage blocks that you measure with have been precision ground to a mirror finish, whereas the non-measurement faces have a dull finish and the dimension etched into the side. I should add that when working with gage blocks, you should wear powder-free gloves, because the oil from your skin can rust the block, altering its dimensions. And always clean the block after you've used it and coat it with a light oil before you put it away.

Anyway, I put the 9mm gage block under the Millimess pointer and zeroed it out by adjusting the height of the clamp first, then by wiggling the Millimess back and forth to move the stem a little, then tightening both clamps as tight as I could do by hand. There is also a fine adjustment screw on the right side which you can turn to set the pointer at exactly zero.

The valve stem was then introduced on the anvil and rolled back and forth under the indicator tip until the largest dimension was shown-- that way you know you've got the tip exactly tangent to the largest diameter of the valve stem.

As you can see, the gage reads -34 microns. One micron is one millionth of a meter, or .001mm (one thousandth of a thousandth is a millionth). So that's -0.034 from a gage block of 9.000mm, or 8.966mm. Now, a grade 2 gage block, which is what these are (you can spend more money for grade 0 but if you aren't working in a metrology lab, your grade 0 blocks will soon become grade 2 when you use them!) have a tolerance of +0.10, -0.05 microns. So that's under a tenth of a micron which I am considering negligible for the purposes of engine rebuilding even though we know it is there. But the point is the significant digits- that 9mm block is actually accurate to at least 9.000, because the tolerance is in tenths of microns, e.g. the block can range from 9.0001mm to 8.99995mm in size within that tolerance grade.

And now the little spec book copyright 1978 by Porsche AG

http://forums.pelicanparts.com/uploa...1175616154.jpg

The spec for mid-stem is 8.97- 0.012mm. Note that this is a one-sided tolerance, which makes sense, because if the stem is any bigger it will either bind or there won't be room for oil for cooling and lubrication. So the range really is 8.970 at the largest to 8.958mm at the smallest. Which is approximately where the markers on the face of the Millimess are. So back to the spec, this reads. . . 8.966mm, so it's just smaller than the max it can be. Which makes sense for an NOS intake valve.

On to the next valve! (It's a lot easier for the next five)

Now, I'm sure somebody is going to say that I should have used a v-block instead of an anvil to measure. If you use a v-block, then you should use a plug gage equal to the measuring diameter. . .which is a whole new set of tools! This is good enough for me!

Great work, John! I would expect that the stem would wear unevenly... did you take a few measurements long the stem to see how the stem wears?

Best regards,

Michael

Michael,

I haven't yet measured any worn valves with this setup, although I just received my spring compressor so hopefully I'll be able to diassemble the heads and start checking things. I'll check all along the stem, that's the beauty of the comparator, it's really fast. For fun I'll use the new .001mm micrometer to check my measurements vs. the comparator setup. Even more fun will be to check the accuracy of the mic against the gage blocks. . .we'll see if it's up to the standards of Mitutoyo!

The new 0.001mic is a 2-3" version with an electronic digital output. I think I should be able to use it to measure the rod bolts before and after stretch. I need to get a good look at the head of the bolt: if it contains an indentation, then perhaps pointed anvils would be required.

ARP specifies a stretch of:

0.0092" to 0.0096" for the 6003 rod bolts used in my 2,0.

In metric, that's

0.23368mm to .024384mm, so let's call the midpoint of the stretch range that you shoot for as 0.239mm, with a tolerance of .004mm either way. So 0.239 + .004 = .243, that's inside the high limit at .00956", or .239 -.004 = .235, inside the low limit at .00925".

Anyway, none of this can be achieved with a .01 resolution micrometer, because the difference between the high end of the stretch range ann the low is .01mm, so you'd end up in between the lines. You'd be stuck buying an English-reading ARP bolt stretch gage, and you'd have to zero it against a new bolt. At a minimum, if you were going to do this, you should measure all the bolts and figure out the deviation, so you would know if the particular bolt you were measuring was an outlier, sometimes happens. That or get the unstretched specification from ARP directly, or if using a Verbus bolt, use the diagram posted in the other thread (if you have a 2,4 with 73mm bolt, that is).

No offense intended but to me this should be called Operation Overkill. It's a car, not a space ship. If you enjoy it go nuts, but I hope no-one reads this thread and thinks this is necessary.

I'm not unimpressed, I just think it's overkill. Porsche, or not.

Excellent! Sounds like the type of work done by the late "Maestro" Harry Pellow.

I also have a bit of measurement fetish when it comes to working the lathe, unfortunately its only accurate to .0002 at 12"

PBH, I'm not offended in the slightest. Certainly plenty of engines have been built and run well without measuring to microns.

An interesting side note is Henry Schmidt's thread about the QC that he does on the QSC cylinders. In another thread, he mentions that he's measured new Mahle Cylinders and determined them to be out-of-round by .0005" to .0008" whereas his own cylinders leave with less than .0002" ovality. Mahle uses air gages to measure, which are capable of measuring in millionths of an inch, without contacting the cylinder bore, avoiding the associated "penetration" when a hard carbide bore gage distorts a comparatively soft aluminum cylinder wall.

Does it matter? Hard to say, because that cylinder distorts into a banana shape when it's torqued down, heated up to 180F and has a piston changing direction 233 times a second inside it. It goes back to the criticism of one Pelican who insisted on using a torque plate for honing cylinders even though it's impossible to replicate the wild thermal load the cylinder sees: you might be doing more harm than good, you don't know until you measure, and you can't measure! Note: many NASCAR engine builders use a torque plate heated to 220F for "hot honing" because they realize that imprecision causes friction which costs horsepower. But that's in a discipline where 1HP may win the race.

Also, Mahle has a different issue in that they use Statistical Process Control to manufacture large batches of cylinders, and it makes economic sense for them to substitute capital cost, in the form of Mahr air gages, for labor cost, in the form of more inspection time. Particularly in Germany, where the labor cost is very high.

That being said, here's my rationale for Project OVERKILL:

1) Most of the factory specs are in 0.001 and they actually show somebody using a Millimess to measure piston diameter in the old workshop manual;

2) I'm not a professional engine builder. I figure if I err on the side of being more accurate and double-check everything, there's less likelihood that I'll screw something up. Also, it's a confidence thing: when I turn the engine over for the first time, I want to hit the starter knowing that I know the condition of every part in the engine; and

3) I, too have a preference for cool measurement instruments.

So no, no offense taken, and thanks for stopping by.

I guess I prefer to go by feel. When my engine smokes or leaks I know it was caused by poor/worn components, no way was it poor assembly. You will have no excuses. :)

Now that you have used the term, please rename this thread as Operation Overkill.

Hey John

I'm loving this thread!

One question

Maybe I am missing something but...Why didn't you use a 0-1" OD micrometer to measure the valve OD? I've done this before and it would seem to be much easier and more accurate.

Tom,

Just wait till I start posting the standard deviation of the measurements. . . -ZZZ- :)

Certainly one could use a traditional outside mic with an 0.01 resolution. You would just have to round the Factory limits in the right direction, e.g. you would scrap any valve that measured less than 8.96, because the low limit is 8.958. I personally wouldn't put a valve in that measured at the low limit anyway.

Once the Millimess is set up, though, it's faster than a mic and doesn't rely on accurate "gaging pressure" the way a ratcheting mic does. In other words, the inspector can't alter the measurement by using too much, or too little, gaging force-- you just lay it on the anvil and the spring in the instrument does the rest. But I admit this is a minor advantage especially if you have a ratcheting barrel on the mic that will prevent you from cranking it down too hard. We know (theoretically) that the part distorts, the anvil distorts and the frame bends open, but those are imperceptible outside of the lab- but you CAN get different readings with a mic if you crank it hard vs. barely get the barrel to slip.

Here is a good online article describing gaging pressure.

http://www.mmsonline.com/articles/0300gage.html

http://forums.pelicanparts.com/uploa...1176121213.jpg

As the above photo shows, the particular crank journal measures 56.471mm. The mic was zeroed on a 50mm standard, because it's a 2-3" version so the scale doesn't go all the way to zero. Of course this is a journal that has been reground 0.5mm under.

During the 20 minutes or so it took to measure the crank, the instrument held its zero nicely. At the end of a run of measurements I would put the standard back in and it lined up at 0.000mm once again. Very reassuring.

Of course there is measuring "feel" that has to be developed: when the standard is inserted you should "wring" it against the micrometer anvil to assure that it's square and that there's no foreign matter on it. Some light oil helps in this regard, but don't overdo it.

I see I made a mistake in the measurement of the valve stems above. According to the Fundamentals of Dimensional metrology book, comparators like the Millimess are most accurate when they are pointing at zero. The further from zero they are displaced, the more error is introduced. So later I'm going to check the Millimess using a gage block to zero it out, then another that is .050mm smaller, then one that is .050mm larger. This way I can verify how much error is in the full-scale swing of the indicator.

When I say I made a mistake, I should have used a gage block stack that was exactly equal to the valve stem diameter, instead of using one bigger and relying on linearity of the scale out at 75% of the indicator's range of motion to give me the measurement.

The rubber is meeting the road finally: the heads are going out and these measurements are required to determine whether the valves are usable, or whether new ones are required at $135 each. A reading of 8.93 when the low limit is 8.938 only causes frustration.

Hey John

Nice charts!!

Hey! You posted before I could give you full credit. :) I added a couple things like the mean and fiddled with the code a little bit. But here goes: "A big shout-out to Tom Butler for creating a spreadsheet that allows you to visualize the specifications vs. the factory limits! Thanks Tom!

Let me know if that's too syrupy. :) In any event, the crank is coming in below the new specs but above the wear limit, and the values are pretty well centered around the mean. So it's off to be magnafluxed, and if it passes that test, a micropolish and balance.

I'm sure that grinding 0.50mm off the rod journals removed the hardening, but 20,000 miles and 25 years haven't hurt things much, unless the journals were barely touched, which doesn't seem likely given how tight the measurements were to a line EXACTLY 0.50mm less than the factory low limit.

Noah: here's the Cliffs Notes version:

1) When you rebuild an engine you should measure all the parts to make sure they are within factory specifications. You don't want to put worn-out parts back in the engine unless you are prepared to run full-page ads in Panorama advertising as much;

2) In order to measure repeatably, you need the proper tools and experience. In my own opinion, the measuring instruments should have a resolution that matches that of the factory specifications. The good news is that these aren't very expensive, particularly if buying used.

On the experience side, the only way you can learn is by doing it, but it helps to have somebody who's done it before to guide you. That's what this thread is all about, an effort to get all the guys with machining and rebuilding experience to share it with the novices like me.

I tried to condense that into one sentence but my fingers got tired. . . :)

Love the graphs. Sure makes it easy to read compared with a list of numbers like I made.

quote: "You don't want to put worn-out parts back in the engine unless you are prepared to run full-page ads in Panorama advertising as much;"

That is Classic!!!!

Why put worn out parts in an engine when MM will do it for you?

From ignorance, not malice: Is the valve length tolerance such that that set-up is required? And what is your zero reference tool?