Topic: Cylinder bore gauge and micrometers

[yogi]

Hey all: I'm doing a top end rebuild on my 1972 CB500 and wanted to make sure the cylinder bore, taper, and out-of-round is within specs. I would like to learn how to do it myself but don't want to spend more than $300 or so on a bore gauge and micrometers. Is stuff in this price range just junk or are they reasonably accurate for the home mechanic? Maybe I should just take it to the shop for this. What do you guys think? If there are decent cheaper good value gauges and micrometers out there, any recs on specific models would be appreciated.

Thanks

[754]

There should be cheaper gauges around if you only occasionally need them.
 Great to be able to check the work, and not find out later it's out of spec.

[70CB750]

I bought bore gauges from ENCO - aint easy to measure the bore.  I kinda called it ok

[kmb69]

I agree with Cal. You usually get what you pay for.
SPI while not the cheapest, but cheaper than the big name guys, is pretty decent middle of the road stuff.

[70CB750]

SPI is the brand I bought from ENCO back when I was working on Red.

[754]

The problem is, without a bore guage you only takes someone's word for what they did.
 With a crappy bore guage, you can see if there is taper, and it needs work, and check that a bore is honed relatively straight.

[scunny]

I've always taken mine to an engine builder, he loves measuring and is going to be far more accurate than me. Free to.

[DaveBarbier]

I feel that cheap Chinese calipers and micrometers and such are actually much more accurate than people give them credit for. But they are definitely more chinsy and that’s why they’re so cheap. Looking around YouTube you see people testing accuracy of many precision tools and they tend to hold up and are repeatable. Will they last you as long as a quality European, American or Japanese tool? Not likely.

I say go for it but try to get the best tool you can. Just know that a lot of time with these kinds of measuring, technique is a big factor.

[PeWe]

Cheap stuff to measure various holes. Maybe too cheap?
https://www.ebay.co.uk/itm/6Pcs-Set-Telescopic-Gauge-Set-Micrometer-Measurement-Bore-Engineers-Kit-8-1-Y2C8/223088021939?epid=16006263800&hash=item33f11511b3:g:zVIAAOSwYSBbZRiU

This can show taper when the needle will jump around
https://www.ebay.co.uk/itm/Dial-Bore-Gauge-50-160MM-Diameter-Indicator-Measuring-Engine-Cylinder-Tool-gbd/382339406420?epid=5011375929&hash=item5905345a54:g:CjwAAOSwtKVaVda0

I have measured my bores with a Mitutoyo bore micrometer I can borrow from my job's lab. I had to measure each bore on 4-6 different heights to see the taper. Numbers to be trusted though. Not cheap.

[70CB750]

You gotta know what you are doing, there are classes in engineering colleges that do just that.  Repeatable results are the minimum to validate your measurements.

[DaveBarbier]

I feel that cheap Chinese calipers and micrometers and such are actually much more accurate than people give them credit for. But they are definitely more chinsy and that’s why they’re so cheap. Looking around YouTube you see people testing accuracy of many precision tools and they tend to hold up and are repeatable. Will they last you as long as a quality European, American or Japanese tool? Not likely.

I say go for it but try to get the best tool you can. Just know that a lot of time with these kinds of measuring, technique is a big factor.

To your point, Dave, a great deal depends upon how accurate your measurement needs to be. If you’re only measuring hundredths, inexpensive measuring tools can be fine. Start measuring to 4 or 5 decimals, and you’ll quickly see how the action of the tool makes a HUGE difference. Especially with micrometers. That’s also why they are typically limited to 1” spans. Gauge blocks are probably a better assessment of how accurate a tool or your technique is. But I don’t know many who own any but instead rely on measurements from their “tool”. I’d wager more than 80% of inexpensive dial calipers are off by at least 0.002 against a quality gauge block. And that adds up pretty quickly when you start thinking about it.

Oh, for sure gauge blocks are a necessity for extreme precision. Though I’ve heard even actual machinists just get Chinese made ones and they’re accurate down to tenths. Or of course go to a flee market and find an old starrett set for $3 from someone who doesn’t know what it is, haha.

As for dial or digital calipers, there’s quite a few videos (even AvE has one) where they put a Chinese one up vs a real quality one and they’re almost identical. But even a mitutoyo or starrett isn’t going to be as accurate as a gauge block.

All that being said, if I could throw away all my Chinese tools and get the good stuff I’d do it in a heart beat of course. I don’t want anyone to think they’re similar quality or that I’m really trying to defend them. I just think for engine work, especially on these old things, you could get by with cheaper. I don’t think engine work has to be that accurate. You’re only dealing with hundredths, which in my limited experience, the Chinese stuff is acceptable.

[kmb69]

I feel that cheap Chinese calipers and micrometers and such are actually much more accurate than people give them credit for. But they are definitely more chinsy and that’s why they’re so cheap. Looking around YouTube you see people testing accuracy of many precision tools and they tend to hold up and are repeatable. Will they last you as long as a quality European, American or Japanese tool? Not likely.

I say go for it but try to get the best tool you can. Just know that a lot of time with these kinds of measuring, technique is a big factor.

To your point, Dave, a great deal depends upon how accurate your measurement needs to be. If you’re only measuring hundredths, inexpensive measuring tools can be fine. Start measuring to 4 or 5 decimals, and you’ll quickly see how the action of the tool makes a HUGE difference. Especially with micrometers. That’s also why they are typically limited to 1” spans. Gauge blocks are probably a better assessment of how accurate a tool or your technique is. But I don’t know many who own any but instead rely on measurements from their “tool”. I’d wager more than 80% of inexpensive dial calipers are off by at least 0.002 against a quality gauge block. And that adds up pretty quickly when you start thinking about it.

To Cal's point, there is also a standard for measuring temperature - normally 20C or 68F. It can make a big difference in actual measurement depending on the size of the part and that particular material's thermal expansion coefficient. Only "Hard" tools, micrometers and such, are actually calibrated to standards in my shop at 20C/68F. All other "Soft" tools, calipers and such, are designated "Reference Only".

In Yogi's and most other cases involving engines, all that's normally needed is a "comparative" measurement where you are attempting to compare pistons to cylinders and such and both items are at a similar temperature within reason of course. The exception comes when you need to relay an accurate measurement to a third party and cannot supply them the actual items for them to measure. Then the measurement needs to be accurately measured to qualified gages and at a mutually agreed common, if not standard, measuring temperature.

I should add that an individual's skill and/or technique can definitely play a factor in both comparative and accurate measurements.

[754]

I agree with what Keith says.
 I bet 90 percent of untrained folks will have a better result with a bore guage than telescoping guage and a mic.
 And remember checking for taper and out of round, you are looking for deviation, not exact numbers.. same with checking a fresh cylinder bore..

[70CB750]

I never trusted dial calipers.  Spent the money on veneer Mitutoyo that has mm and inches when fhe old Somet from my dad did not cut it anymore. 

[johans]

all of my micrometers and bore gauge are made by Central .  This is the same one i use , works great .

https://www.zoro.com/central-tools-cylinder-bore-gage-2125-7-6460/i/G1706490/feature-product?gclid=CjwKCAjwt7PcBRBbEiwAfwfVGKRJmbWWQGFQdbx9__OIeZbE3UOeqHn6eFsgQZXcH0HwKdOoeKTr8RoCzkkQAvD_BwE&gclsrc=aw.ds

nothing like doing it yourself with a quality tool.