Inside michrometer for measuring bearing clearances
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Inside michrometer for measuring bearing clearances

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    Senior Member holorinhal's Avatar
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    Default Inside michrometer for measuring bearing clearances

    I have read a few of the threads on measuring bearing clearances.
    I have read that some prefer using inside mic's with out side mic's, rather than a dial bore gauge.
    What type and brand of inside mic, would you use, a straight style( for lack of a better word), a telescoping snap gauge, a tri point mic or a mic with the outward facing points( again for a lack of a better word)?














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    Some guy obnoxious001's Avatar
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    The advantage a dial bore guage has is that you can set it to the outside micrometer reading for a journal, the use to not only check bearing clearance, but also taper and how far out of round the bearing is in the housing.

    Many, many years ago, before I bought a dial bore gauge, I used snap gauges. In my opinion it's quite a bit more tedious, since you have to carefully set it, pull it out and measure with the outside mic, then go back and double check, or check another angle, etc. I don't think you will be quite as accurate, but if you are careful, you should be able to use them to verify clearance.

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    gn7
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    Like Barry said, they all work, and they all can be pretty accurate. Its all in the user. I can get pretty good readings with snap gauges, but its a PITA, and time consuming.
    Inside mics work, but I never use the number on the mic, I check it against the mic I used on the crank and compare the two to get the clearance.
    I still actually prefer them for crank work, but the bore is small and narrow, and frankly I don't get to hung up in the "side" measurement. It is what it is. I only care about the vertical clearance, and the front to back saddle bore measurement before the bearing went in the block to check for bore taper.

    For cylinders, like Barry said, you can check the bore top to bottom relatively quickly with a bore gauge. Again, I check it against the outside mic, or a standard I measured with the outside mic.
    However, if the block was honed with a deck plate, and you measure it with the heads off, you can get numbers that can be down right scary. Specially if you spin it to check roundness, Because it won't be, specially up near the deck.



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    Default As mentioned..

    I've found the quickest/easiest way is use the "outside" standard Mic, set at the journal size to "zero" the dial bore gage. Measure the journal, "lock" the mic and carefully set it up in a bench vise with padding, then "zero" the bore gage using the "just measured" and locked mic...
    Once zeroed, measure the bearing ID, and you'll see the clearance directly on the dial.... I would add that you "plan ahead" when measuring the mains so that you have room to measure without other caps being in the way... AND, a BIG and, be sure to fully support the big end of the rods while torquing/untorquing them... Rods WILL twist if not properly supported... I use a set of custom made aluminum "jaws" in my Kurt mill vise and leave just enough room to get to the bolts/nuts...
    Ray
    PS Hal, if you're using NEW ARP bolts be sure to measure, and RECORD, the "new" length before you even start. List the bolts, and the rod numbers, as well as "tang" side.... Oh, and remember to use the .0001 readings on the back side of the mic barrel... Yes, it's THAT critical.... If those bolts are ever reused, you'll need those numbers to assure they haven't "grown"...... 2nd OH yeah, wear plastic gloves while handling the ARP bolts...
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    Senior Member wizbang's Avatar
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    Micrometers are all about the hands. If your a big brute type person and you can't get the "feel" correctly, you may end up with big/little readings.
    Practice is your friend !

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    Senior Member Franger's Avatar
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    GREAT THREAD

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    steelcomp was here
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    The tri-mic you have pictured is awesome for lifter bores.
    Telescoping gauges, IMO, are last choice for places where you can't get an ID mic.
    Bore gauges can get you in trouble if you're not spending the coin on a very good one. I have a fairly expensive one and it's caused me problems. I've since put it away and now use inside mics and C mics. I use the inside mic sort of like a telescoping gauge. I set it, then measure it with the C mic. My inside mic is very similar to the second on in your pics. Dial bore gauge is faster, but IMO you shouldn't be in a hurry doing this sort of thing.
    ID mics and C mics are pretty fool proof but as mentioned, they take practice and feel. They are also very temperature sensitive if you're measuring tenths or less.
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    Super Moderator HammerDown's Avatar
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    Ambient temperature changes...I could believe what a temp swing does to parts and what the mics show
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    Quote Originally Posted by HammerDown View Post
    Ambient temperature changes...I could believe what a temp swing does to parts and what the mics show
    Just hold a mic in your hand for more than a minute and then re-check it on your standard. You do that frequently, right? Check your mics with the standards?
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    Senior Member wizbang's Avatar
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    We have to hold parts for 24 hours in a climate controlled room to measure them at work !

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    Distinguished Member David 519's Avatar
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    Quote Originally Posted by gn7 View Post
    Like Barry said, they all work, and they all can be pretty accurate. Its all in the user. I can get pretty good readings with snap gauges, but its a PITA, and time consuming.
    Inside mics work, but I never use the number on the mic, I check it against the mic I used on the crank and compare the two to get the clearance.
    I still actually prefer them for crank work, but the bore is small and narrow, and frankly I don't get to hung up in the "side" measurement. It is what it is. I only care about the vertical clearance, and the front to back saddle bore measurement before the bearing went in the block to check for bore taper.

    For cylinders, like Barry said, you can check the bore top to bottom relatively quickly with a bore gauge. Again, I check it against the outside mic, or a standard I measured with the outside mic.
    However, if the block was honed with a deck plate, and you measure it with the heads off, you can get numbers that can be down right scary. Specially if you spin it to check roundness, Because it won't be, specially up near the deck.
    Spot on IMHO.... I'd invest in dial bore gauges if I built a lot of motors or was doing it for $$$. For the number of motors I build, T gauges/inside mics are fine...
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    Default The used parts hunt

    When I'm out on the hunt for blocks, cranks, etc a good tool to have is a quality pair of calipers. Always good to check the claimed sizes for yourself before dropping any coin. They will give you a quick reference. Kinda like "measure twice-cut once" rule of thumb. I'm guessing most all wrenchers on this site propably have a pair or two in their boxes.

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    Senior Member Hass828's Avatar
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    I have a dial bore guage, snap gauges, mics & stuff, but for the novice, or just to double check you work its hard to beat the old plastiguage. One thing you can say for it, it removes all of the variables and will show taper.
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    I have to disagree with plastiguage. I have been lied to too many times to use that stuff. Old guage gives terrible readings. Even if you buy a new stick it can be old stock and worthless. I guess if you have
    nothing else to use. But if that's the case you better really trust your machine shop.

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