The V8 Owners Forum -

Im looking to buy a new micrometer. Ive noticed there are loads on flea-bay for about 4 quid. Are these accurate enough to use on an engine - they just seem very cheap..anyone used these or have any opinions..

I would say no but post a link to one anyway.

here it is

http://cgi.ebay.co.uk/6-Digital-Caliper ... dZViewItem

Oddly enough, that's exactly the same one I have - I had a different version beforehand and had no issues either

The new one always returns to zero as well after extension, which suggests it's quite well built.

Certainly a solid bit of kit - no complaints here!

They are only 4 quid but they charge you 5-9 quid for postage to make up the profits

cool... i'll get ordering...

Verniers are very difficult to measure engine parts like cranks with. You would be better off with a micrometer for that.

Right, Lets put my engineer head on, Lets get one thing correct first, its a digital Caliper, not a micrometer,
The caliper has a few advantages over a micrometer, and a few disadvantages,
Advantages, its a bit of a all in one measuring machine, can do limited bore measurements, O/D, length and depth
Any measureing equipment is only as good as its sum of parts, Cheap measuring are only as good as the original machining of the components within that tool, calipers in particular are reliant on a precisely machined rack and pinion and if that is machined incorrectly with the wrong pitch, the whole caliper reading is incorrect compoundly along its length, if there is a 10th discrepency in its first 10mm after 100mm you have a 1mm discrepency, for this reason they are also subject temperature variation as the rack expands or contracts in length, for this reason any engineering quality control is kept at a constant temp of 68degs?.
Disadvantades, they are hard to get to read accuratly as they do not self align when usd and held at a slight angle they will give an inaccurate reading, you cannot measure bores more than 10mm into the bore, and the external jaws are suspectable damage if they are dropped.

thank you for taking the time to explain that to me Ian. thats one of the things i love about this forum - very helpful people..

ian.stewart wrote:Right, Lets put my engineer head on, Lets get one thing correct first, its a digital Caliper, not a micrometer....

No, no, it clearly says it's a digital caliper vernier micrometer gauge.

I agree with everything you say, plus the fact that the uninitiated user will take what the digital display says as gospel, regardless of how the reading was obtained. I used to work for a machine shop foreman who would measure, ferinstance, the 'centre' to 'centre' of adjacant bored holes I had just machined out, using his new fangled digital caliper, and then tell me they were 0.002" out.


As far as he was concerned it had to be correct, as the readout said it.

A digi caliper is certainly a very useful tool to have around but certainly for accurate measurement of engine components during assembly you should be using micrometers. Digi mics are available (not for 4 quid tho!) but I have not used them. Anyone here had good experience with them? I guess being able to switch imperial to metric at the touch of a button is some advantage.

Yes I have sets ranging from 25mm up to 150mm and got them from ebay but not for 4 quid each. When I measured my crank I found a 1/2 thou ovality on a main journal just to be sure I took it along to my machine shop and they got exactly the same. I was chuffed not only because the digi mic was accurate but also because I had measured it properly. I will dig out the receipts and see if the seller is still around and post for anybody interested.

Should also add yes the imperial metric conversion is handy. My lathe is imperial but my head mainly works in metric so they are great for that. Someday I will get a set of digital scales for it but they are ££££ so will have to wait.

Ive got a set like those also - work fine. My lathe is imperial and I use them for doing the conversions also.

You know, I'm old. I use a vernier caliper, and I don't have any
problem micing cranks, cams, pistons, and other goodies involving
engines. Why can't you young punks get with the program??

(I say this in jest...)

canzus wrote:You know, I'm old. I use a vernier caliper, and I don't have any
problem micing cranks, cams, pistons, and other goodies involving
engines. Why can't you young punks get with the program??

(I say this in jest...)

Lets be clear, vernier calipers are not for checking engine internals (crank journals, pistons, bores etc) - only Micrometers can do that properly.
However those cheapy digital ones are handy round the workshop for general use etc - I find them quicker than trying to squint at a tiny line on conventional verniers when making things.

They are called veryneers for a good reason.