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Cylinder bore measuring

Bore Gauge

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Graham Williams 1121/02/2020 17:49:29
61 forum posts
40 photos

Chuffed today received a Russian 4 point Bore gauge, all the way from Bulgaria of all places, measure down to 2 microns in the range 10 - 18mm which covers all engines I'm likely to have an interest in. No guessing now as to how much pinch I've managed to get when lapping liners. Made a new liner for an AM 25 last few days, gauge saying 25microns pinch so well pleased

bore gauge.jpg

Edited By Graham Williams 11 on 21/02/2020 17:51:41

old mart21/02/2020 19:12:05
1540 forum posts
136 photos

Have you got any ring gauges in that range to set it with?

Alan Vos21/02/2020 19:36:02
148 forum posts
7 photos

Ok, I'll take the bait. This is 4 point. All the new bore gauges I see on sale are 3 point. Does anybody know enough about measuing holes to compare and contrast. I note CCCP on the paperwork.

I like being able to measure things far more closely than I need, but even budget brand bore gauges are !!! expensive.

Graham Williams 1121/02/2020 20:09:24
61 forum posts
40 photos

Don't need a setting ring as just trying to find the difference between top and bottom of any liner. Choose 1 of 3 'probes' to suit bore set reading at one end to zero and then measure other to show the difference + or - basically a comparator, if you need a setting ring the guy has all sizes though quite costly. Was told by one who knows that the 4 point was superior and used by all the top combat engine makers (Ukrainian/Russian)and easier to use and so far I've found it easy to use. Was only 100 dollars delivered, they do like dollars, he had others that were cheaper. Searched online after only finding ones that didn't have the required scale and they all looked well used, pricey and used a different system to measure which looked clumsy.

Old School21/02/2020 20:36:00
325 forum posts
27 photos

Looks a useful bit of kit. Wouldn't mond measuring some of my liners. Roundness seems to be my problem with used liners the only real test is to make a new piston and run them.

Ramon Wilson21/02/2020 20:45:34
725 forum posts
81 photos

Lovely find Graham thumbs up - most envious

No excuse now for that perfect liner eh wink

Regards - Tug

Kiwi Bloke22/02/2020 02:17:40
405 forum posts
1 photos

I'll try to reply to Alan's question...

The pic doesn't show the working end of the gauge, so it can only be an assumption that this is a standard 4-point-of-contact bore comparator, in which the two non-moving points are set on a chord of the cylinder, and the other two points oppose each other, lying in a line that perpendicularly bisects said chord and thus define the diameter of the cylinder. It is this diameter that is gauged.

3-point-of-contact bore micrometers have all three anvils moving, 120 deg apart (resembling a Mercedes Benz motif). And yes, they are horribly expensive, even used.

Graham Williams 1122/02/2020 06:35:17
61 forum posts
40 photos

Hi Kiwi. I/we do use it basically as a comparator but it is capable of measurement, that is what it's designed to do.

All 4 contact points (balls) move and are in contact with a central precision? made tapered spindle. I'll take pictures of a 'probe' and post later and perhaps you can tell me whether the design is superior or not to the 3 point type, which as you say are much more expensive and unless you have a no expense spared approach to model IC engine making putting them outside what is reasonable, in my opinion, to spend, Also I didn't want a micrometer (barrel) type as I wasn't confident in getting repeatable readings as all mikes, again in my opinion, depend a great deal on feel. For example measuring a liner with an ordinary inside mike I can get readings that differ by a thou maybe more taking one reading after another, heavy handed or what but it caused problems for me doing it that way. Also ball and telescopic gauges gave differing results so a decent dial bore gauge, economically priced with micron capability, looks good from here.

Hiya Tug. Don't know about perfect but being able to decide on whether you've got the pinch to a working position looks easier to decide on with this gauge. Never underestimate the Russians on producing good stuff, look farther than a cold war Lada lol. Finished with the AM25's now so sorting material for the Holly Buddy engine, think I'll do the liner first LoL.


Graham W

Edited By Graham Williams 11 on 22/02/2020 06:37:55

Graham Williams 1122/02/2020 07:45:48
61 forum posts
40 photos


Kiwi Bloke22/02/2020 08:49:32
405 forum posts
1 photos

Fascinating Graham; never seen one like it.

I'd still call it a comparator, however, although, like the more conventional bore comparators, quantification of deviation from the null can be read from the dial. That isn't really the same as a 3-leg bore micrometer. As to why the Russians used four moving (and apparently gauging) contact points, I've no idea. They liked to plough their own furrows, didn't they? Perhaps someone can offer a suggestion.

Regarding inconsistent results from different measuring device concepts, I have to agree. I have a set of tiny Matrix 3-leg bore micrometers somewhere (not accessible at present). From memory, there is a fairly conventional-looking micrometer thimble, which sets the extent to which the legs can move out, under the influence of a spring. There's a set of different diameter heads, containing the legs. They are expanded by a shallow-tapered pin, the axial position of which is controlled by the mic. thimble. The pressure applied to the work is that of the spring, not the gorilla holding the device. In use, one moves a collar axially, to retract the legs when inserting and removing the device. Neat. Unfortunately, to span the entire measurement range, several pins are required. One is missing. It will be an awkward bit of watch-making to fashion one. It's not high up on the (infintely long) to-do list.

Bob Brown 122/02/2020 12:11:35
1010 forum posts
127 photos

I have this for measuring bores 0.4" to 1.4"image00003.jpg

Graham Williams 1122/02/2020 13:08:17
61 forum posts
40 photos

Hello Bob. Got something similar to that but it's graduated in thous as yours and was trying to get the taper in the liner to give 20 -30 microns pinch bottom to top so didn't work for me, no better than an internal mike.


Graham W

Andrew Johnston22/02/2020 13:58:07
5413 forum posts
627 photos

Seems a bit odd. A circle can be uniquely defined by three planar, and not co-linear, points. Anything more is over-constrained. So three measurement points are guaranteed to sit exactly in a circle. A fourth point cannot be so, unless the circle is perfect. That's the reason most bore micrometers have three points. In all cases the measuring instrument has be aligned with the bore axis to get an accurate reading. With four points, and assuming the circle is near perfect, then it may be easier to judge when the instrument is aligned?


Martin Connelly22/02/2020 16:27:26
1251 forum posts
152 photos

This is my Fowler Bowers 3 point 0.75" to 1" bore gauge. I also do not have a ring gauge to check it against.

Bore gauge

Martin C

Graham Williams 1122/02/2020 16:59:32
61 forum posts
40 photos

All very interesting as the guy in Rowan & Martin's show always said. Tried it out again this afternoon on 2 liners I've made and what I've got is exact repeatable readings on multiple attempts, gauge hand held so it's what I'm going to use from here on in. As to why the Russians went for 4 contact points I have no idea but I've always had a healthy respect for Russian technical products, were they not at the forefront of CMM introduction, they do indeed plough their own furrow and because of a desire for usually Dollars the products are within reach price wise.

Martin, will your Fowlers gauge measure in microns? I'm not a fan of barrel (thimble) measurement for anything needing sub thou measurement for the reason I said previously.

gerry madden22/02/2020 17:05:46
106 forum posts
45 photos

Machining processes don't of course produce perfectly round rings or bores and these types of error become more significant when working with fine tolerance parts like bearing rings. All machining processes will cause 2, 3 and 5 point lobing (and other harmonics if you look harder) with the magnitude error dependent on the machine and the process used. With 3 point gauges or vee blocks you can pick up on or avoid these errors by carefully defining the angles between vee flanks or pins on a 3-point bore gauge to suit the typical shape of the parts you want to measure.

Having said all that, I've never come across a 4 point bore micrometer either and I cant quite see the benefit. I can only guess therefore that the purpose of a 4-point device is just to make the process of getting a simple 2-point measurement a little more accurate than it usually is by minimising the operator error. ...but I may be quite wrong


Martin Connelly22/02/2020 18:48:48
1251 forum posts
152 photos

The Fowler gauge is marked to 0.00025" (quarter thou) and you could theoretically estimate between the marks. Not having a temperature controlled workshop or inspection room I doubt I will worry about microns.

Martin C

Ramon Wilson22/02/2020 19:02:29
725 forum posts
81 photos

I don't want to appear dismissive here guys but are we not going off the beaten track here a little - surely this device can be seen as Graham first described it - a 'gauge' or comparator - it certainly isn't a micrometer. No different in principle to Bob Browns Mitutoyo gauge just vastly superior.

To use it as a measuring device would require zeroing it to a known source ie a ring of specified diameter. Precision ground setting rings should be provided with three point micrometers to establish 'zero' like any micrometer standard but are not 'standard issue' for bore gauges

Just been and checked my Mercer 3 point bore gauge - instructions are clear - set gauge to 'datum ring' (not provided), rock about center to establish 'zero' then use on bore being machined to estabish size. That datum ring can be machined from mild steel to as fine a tolerance as wished to the nominal size required - it does not need to be hardened and ground - and will see many bores 'sized' before wearing

I have a Mitutoyo gauge the same as Bobs but find it very hard to establish an accurate zero to give the kind of accuracy required for the kind of bores that Graham is referring to. A bore for a compression ignition engine, as I'm sure that those who have made them will attest, requires a very fine tolerance on measurement and roundness.

Personally I would love to have a set of three point mics to cover the ranges usually machined but desire and expenditure are a million miles apart I'm afraid.

Good luck on the liners Graham however many you makeyes

Regards - Tug

Neil Lickfold22/02/2020 19:15:14
593 forum posts
102 photos

The 4 point ball comparator will show the error of a 3 lobed hole and a hole reamed with a standard reamer that is not round. Plus if careful you can use a micrometer or a slip stack to set the gauge with. The concept of the Russian style ball and pin style gauges, is that you can have differing arrangements of the ball orientation. The one I have, the pin slides in the assembly is quite a neat fit, but slides. The ball is also a very close fit to the mandrel. It works really well. Of course, there are many options to try and measure something, and what you are looking for will determine the type and style of bore comparator or bore micrometer being used. The more accurate you are trying to get, the more difficult it becomes to measure. The greatest difficulty is not the exact temp of the work environment, but the stability of that temp. To get back to a standard size, you can calculate how much bigger the item should measure from the standard of 20 deg C.

Graham Williams 1122/02/2020 19:20:15
61 forum posts
40 photos

Just a thought Martin, what would the micrometer gauge you have cost, I've never heard of one I'm afraid. The advice I've had pointed me in this type of instrument as the one routinely used and it is easy to use where all the other gauges I've tried never gave me anything satisfactory and were quite variable in use. Cost to me is also a consideration as Tug says and if I had to guess the Fowler tool would cost more, maybe considerably more, than the Russian tool and it would in my opinion still be subject to my lack of feel.


Graham W

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