What's the minimum I need to measure engine clearances

robk46

New Member
Like the title says, what do I need to buy to check my journal and bearing clearances? How accurate should they be .001 or .0001 of an inch? Should I get a 2"-3" micrometer and a 6" caliper?
 
The best way to do it is to get a 2-3" mic and get a dial bore gauge. This will get you 0.0001". No need for calipers. A dial indicator is good to have to measure end play was well.

Chris
 
Be certain to buy Starrett, Mitutoyo, or something of equivalent quality(German, Japanese or American). The accuracy of your measurement is all in the way your gauge is threaded, and crap the chinese/taiwanese turn out doesn't get it. The words, "precision" and "quality" don't seem to translate well into their language.
 
You will also need a ball-anvil micrometer for measuring those pesky curved bearings!
 
If you want another opinion just use Plasti-guage. After taking machining classes in tech school I found out that if you have six people measure with a micrometer you'll probably get at least four different measurements. If you are off a little measuring the crank journal and off a little measuring the bearing id you could have a problem. Mics are great for the pros but not a novice.
I've built quite a few of these motors with Plasti-guage and never had a problem.
Randy
 
I have found Plasti-gauge to work VERY WELL when one follows the directions on the package. I have used it as a sort of second opinion and it always jives with my mics...the several times I have tried measuring both ways.
 
I have found Plasti-gauge to work VERY WELL when one follows the directions on the package. I have used it as a sort of second opinion and it always jives with my mics...the several times I have tried measuring both ways.


both systems have their limits-------assuming good quality measuring tools (starrett, brown and sharp, mitutoyo etc) it takes a little practice to prevent errors that creep in on the fourth decimal place ie. tenths of a thousand------it helps to make sure you calibrate the bore gauge with the same mic that you measure the journal with------this method is limited only to tool quality and experience with precision measurements--------as for the other method it is VERY important to know there are two different and distinct types of plastic gauging------- they will correlate very close to the the measured dimensions with mics/gauges as long as you know each types greatest weakness-----there are two distinct types-----notice the spelling------for instance the commonly used "green" that is sold for .001 to .003 is made in the US and sold under the "plastigage" name will exhibit accurate values as long as you don't trust it below .0015--------it cannot resolve the difference between .0005 and .0012-------you CANNOT interpolate things below these limits or you can end up with some tight bearings and think you are safely at .001 or above------there is an English made brand spelled "plastigauge" that works well from just slighty below .018mm (about .0007") to about .030mm even though it is sold as working good up to .045mm-------drawback is that it comes with metric scales but it is easy to convert---------word of caution!!!don't trust this brand above .015"----------i once did a very detailed test to confirm this------I used lab A grade gauge blocks seperated by precision ground shim stock and put them in a press-------confirmed all the measurements with my $30K pratt and whitney supermicrometer accurate to 0.000002"------i cheaped out and didn't go for the $10K option that makes it accurate to 0.000001" cause i was pretty sure the extra millionth of an inch wouldn't matter much on a buick motor------want to see what a 150 lb micrometer looks like check this out------its not something you want to drop on your toe ---- pratt and whitney supermicrometer -------spent days on this cause i take it a little too seriously-------one of the problems with being o.c.d.-------want to see some of the test results let me know...............RC
 
I bet you can measure the difference between:
something that is sitting around a cold shop, and,
after carring the same part around in your pocket for a while!
------------------------------------------------------------ a few dashes for you! :)
 
I bet you can measure the difference between:
something that is sitting around a cold shop, and,
after carring the same part around in your pocket for a while!
------------------------------------------------------------ a few dashes for you! :)

no need to carry them in your pocket------actually at this level of precision you can put a part in the supermicrometer and if you hold your hand on it you can watch it grow--------and to make any stable measurements you have to keep the room, mic and parts at a constant 78 degrees--------to make any real use of a mic like this in the real world you just have to ignore most of the decimal places..........RC
 
A 6" dial caliper, dial indicator with magnetic base, and a set of micrometers is all you should ever need unless you own a machine shop or are a machinist. You can buy small sets of micrometers, they can have 0-1, 1-2, and 2-3 inch. rodman99999 hit it on the nose about buying high and/or upper quality pieces, not much point in having a accurate measureing device if its a piece of crap or even plastic. A dial bore guage is not needed unless you have a boring bar or power hone, they are expensive, just use your dial calipers to get a rough bore size. Leave that tool to the machine shop. The next piece of advice I would give is practice, practice, practice!!! with these tools it is very easy to take a wrong measurement. Not something you want to do on a higher horsepower engine.
 
True about the practice. Measure several times and if ya can't repeat the measurement - something wrong.

Make sure the set comes with standards - and set the mics frequently.
 
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