Mitutoyo 2 in to 6 in Borehole Gauge

I added this tool to my tool kit so that I wouldn't have to rely on a friend for measuring cylinder bores. It finally arrived today and I've been trying to figure how to use it. The instructions are the worst I've ever seen for anything. Just a couple of sketches to illustrate what it should look like. No actual instructions on how to use it. Their website is just as bad. So I'm looking for help on whether I'm using it correctly.

This is a photo of the gauge. I'm trying to measure a KZ650 cylinder bore with a spec of 2.4407 " to 2.4411 ", with a limit of 2.4449 ". I am using a 2.362 " probe with a 0.08 " washer, giving me a measurement diameter of 2.442 " The gauge is a bit tight, as expected. In fact I think the gauge always had to be a bit more than the bore in order to get a good measurement.



The dial indicator was zeroed with the small gauge on 0.05 " and the outer dial on 0.0000 ".



Once in the hole the gauge measured minus 0.069 ". When I subtract this from the total gauge probe length I get 2.373 ". This is well under the spec so I assume I've done something incorrectly.



Last photo shows the gauge instructions....Item 4 in the photo. Nothing specific, just some illustrations to show how to calibrate etc.



Does anyone know how this thing should work?

1) find the right combination of extension length such that when you insert the bore gauge into the cylinder sleeve you have needle movement but it doesn't run out of travel.

2) get a real deal micrometer, one that reads in .0001" increments and is properly trustworthy. Adjust the mic until it's exactly on the nominal bore size: 2.4409" (62mm)

3) Insert the bore gauge probes between the mic anvils (yes, it's fiddly) and rotate the dial until the pointer indicates 0

4) Carefully remove the bore gauge from the mic and insert it into the cylinder sleeve bore

You can now read the bore size by adding the reading on the bore gauge to 2.4409". Wobble the probe back and forth so to speak and look for the smallest reading so to speak. That's how you know you found the proper diameter at that point in the bore.

Check in various places in the bore, at 90 degrees from each other, and top and bottom of the bore. There should be no more than .0010 out of round or taper. The actual bore size is less important. If the out of round and taper are okay, so will be the bore size.

Interestingly, when doing this on my KZ750 I found the bore over nominal, even when measuring in locations in the bore where the piston doesn't travel (such as at the very top.) WTF? I still don't understand that other than to blame Kawasaki about not caring.

At the position in the bore below the dial shows .0017" over the nominal bore size.

P1010960 by nessism , on Flickr

Piston fit by nessism , on Flickr

I'll try your method but first I have to get a larger micrometer. Mine are 1 in ch and 2 inch only.

After reading your method it seems to me that you are putting your borehole gauge into the micrometer just to set your gauge to zero at the nominal width of the cylinder. Am I understanding it correctly?

If so, then what I was doing should work.

I start with a known dimension for a particular insert. (This dimension is slightly larger than the borehole.) I insert the gauge and read the change in the dial gauge. This number is subtracted from the known dimension to get the borehole size. Does that sound correct?

hardrockminer wrote: After reading your method it seems to me that you are putting your borehole gauge into the micrometer just to set your gauge to zero at the nominal width of the cylinder. Am I understanding it correctly?

Correct.

If you can't get your hands on a good micrometer, you could insert the gauge and move it around until you find the smallest diameter, most likely near the very top of the cylinder (be sure to remove any carbon,) and then set the dial to zero. Then move the gauge around top to bottom and at 90 degrees to each measure point, recording how much out of round and taper you find. These are the important measurements. You can't determine bore size this way though, for that you need a mic.

BTW, the FSM references measuring the bore in various places and making sure any two points don't vary by more than .0020." Personally, I prefer to think in terms of out of round and taper independently, not as a combined feature. For new bores they reference a max difference in measurements of .0004."

Nessism, thanks for your help. I would think the least worn part would be near the taper, on the bottom. The cylinders don't travel down that far, but they do travel right to the top, although the top ring doesn't travel that far.

I ordered a 2" to 3 " gauge today, but won't have it for a couple of weeks. I'll redo my numbers when it arrives. The book says to measure 10 mm, 60 mm and about 90 mm below the top. I have all the specs on out of round, etc.

Yes, the micrometer replaces the "master" in the instructions. You zero the bore gauge first then measure the bore. I take 6 measurements, bottom, middle and top (below the ring line) 9-3 oclock and 12-6.

I measured today using the bottom of the barrel to "zero" the gauge. I zeroed twice for each barrel...once in the forward/reverse direction and once in line. (at 90 deg) There is some wear in each cylinder, increasing from bottom to top of the bore. If this was a keeper bike I'd probably bore and hone, but it's a build and sell, and I want to keep my investment to a minimum so will go with the cylinders as is.

I also ordered the 2" to 3" micrometer today. It's coming from Vancouver so should be hear in a couple of days. Will repeat the measurements when it arrives.

Setting the gauge with the bore you are only measuring taper. You need a micrometer, or gauge block, to use the tool properly.

Just a little information for you, even though Mitutoyo says that these dial bore gauges are precise(which don't get me wrong, they are). Any tech from Mitutoyo will tell you that you should always set your sizes off of a outside micrometer for these DBG's. Setting it by using the instructions is just a backup for the "in case you do not have a micrometer" problem. I've been a machinist for 12 years and I know it's always easier to use a outside mic to set your size. Once you have both a DBG and a outside mic, measuring bores is a breeze. Just count yourself lucky you don't have to measure bores with a inside mic. That's a real pain in the ass.

Thanks to all who contributed. I bought a Mitutoyo gauge because I knew they made quality products and I didn't want to buy Chinese made junk that is far cheaper. (I avoid buying anything from China.) The instructions provided with the gauge are horrible, and that's an understatement. Mitutoyo needs to spend a little money on their instruction manuals.

Steel Legion wrote: Just a little information for you, even though Mitutoyo says that these dial bore gauges are precise(which don't get me wrong, they are). Any tech from Mitutoyo will tell you that you should always set your sizes off of a outside micrometer for these DBG's. Setting it by using the instructions is just a backup for the "in case you do not have a micrometer" problem. I've been a machinist for 12 years and I know it's always easier to use a outside mic to set your size. Once you have both a DBG and a outside mic, measuring bores is a breeze. Just count yourself lucky you don't have to measure bores with a inside mic. That's a real pain in the ass.

Trying to follow along here, got lost at DBG.