measuring valve guide i.d. with digital dial bore gauge.

[JOHNDOE333]

Hello all,

The facility that I work at requires valve guide wear to be measured before and after engine testing is performed. One of my co-workers does this procedure and using a digital dial bore gauge with a seperate but wired button to snap shot the reading onto a computer for proper documentation and instant calculation of stem to guide clearance once the stem diameters are inputed as well.

When I have done this in the past I have used an analog dial bore gauge and always found the point that the needle changes direction to indicate the tightest spot. This employee in question inserts the gauge and pushes the button to record the data and never looks at the gauge reading at all. The gauge does not appear to be self centering. My question to you is...does a self centering one exist or should he be looking at his numbers before pulling the trigger? I played with the gauge the other day and managed to get a variance of .070 from one extreme to the other.

Good day,

 

[FoMoCoMoFo]

sounds like whatever he's doing it's well documented. have you looked at the results? are there lots of guides that are to small to fit a valve ?

 

[JOHNDOE333]

His readings are fairly consistent. However, we did have to replace a head the other day that was slightly out of spec and had only about 3000 miles on it since new. It also passed inspection the first time around. The difference between being able to use the head and replace it was about .0003 (3 tenths!). I was able to get alot more variance than that just by moving the gauge around slightly in the guide.

Good day,

 

[FoMoCoMoFo]

Well then, You may be dealing with a skilled individual who has developed a "feel" and can accurately locate that gauge blindfolded.

 

[patprimmer]

What actually is your question.

Is it your responsibility.

If you conclude he is inaccurate, what can you do and what will you do.

Presuming you can and should do something, how about, without his knowledge, sending a few heads through a second time to see how repeatable his results are.


Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[JOHNDOE333]

My question was clearly stated in the first post. Does a self centering digital dial bore gauge exist? None the less. I do appreciate everyone's responses. Part of my issue is the accuracy of the whole thing and second is moral with regards to saving the company money if the head never had to be replaced at all. The brand is a mitsutoyo (spelling?). Just by looking at the design it appears that it has no way to align itself in the guide, so there seems to be alot of room for human error. Thanks again for everyones time.

Good day,

 

[evelrod]

Silly me. I guess I've been doing it wrong all these years (or have not developed that "magic" feel). I use analog Mitatoyu and a Stearett (sometimes my old Brown and Sharps vernier). I usually measure three or four places and record the average. Seems to work for me, at least for the last 50 years or so.

Rod

 

[FoMoCoMoFo]

I don't know of one, you've proven that it's possible to make errors on the order of 10-20 times the tolerance but he's getting consistent results. or not ?

 

[FoMoCoMoFo]

I'm sorry that's closer to 1 or 2 hundred times.

 

[patprimmer]

Sorry I missed that line.

I stick by my comment, if it is your place to do so, send some back to test his consistency.

If it is not your place to do so, you could very easily end up with a lot of egg on your face.

Despite your intentions to protect the company, it might be seen as disloyalty toward a fellow worker and undermine the trust others might have of you.

I might be way off base, but that was the feeling I got from reading your OP.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[cheapcharlie]

sounds to me like someone has found a way to pass a lot of loose guides if readings are just taken from near center.

 

[dicer]

I have a question first, is this a big outfit? The correct way to map the wear profile would be to use a CMM. And I'm sure you are cleaning them real well before measurements are taken. Any openings there?

 

[MikeHalloran]

A digital gage removes the uncertainty associated with reading an analog gage. It does not remove the uncertainty associated with properly setting up the measurement.

We can't tell from here if the individual in question is highly skilled and productive, or fast and sloppy, or enthusiastic and sufficiently skilled but lacking a proper procedure.

We also can't tell if any of this is your responsibility, or not.




Mike Halloran
Pembroke Pines, FL, USA

 

[anyoldname]

Mitituyo make all sorts of tools for measuring bore ID, their Borematic range is what I think you're looking for, thay have at least 3 feeler blocks that expand out to make contact with the walls, centering the tool, the ones I've used in the past are accurate to 0.5 microns.

http://www.mitutoyo.com/TerminalMerchandisingGroup.aspx?group=1524

 

[evelrod]

Mike, I guess your correct about the removing the uncertainty of a "reading error" by the tech. On the other hand, the digital mikes that I use are "quick and dirty", but I find that I spend as much time double checking the "zero" as I do double checking my measurements. I guess I'm just a bit too old to have the faith in the digital stuff....However, I looked at that Mitutoyo and, I GOTTA HAVE ONE A THEM!
I know, too many toys already.

Rod

 

[sreid]

Air gages are effectively self centering and can be made to measure ID's at several locations in a bore.

 

[GregLocock]

The way to find out if the measuring system is producing menaingful results is called a gage R&R study. Basically you'd get a small number of different heads measured by a small number of different operators, a small number of times, and then do some stats on it. That'll identify whetehr the procedure, or the operators, can really measure the difference between heads.

In my experience many accepted measurement practices on the shop floor are only just able to measure the difference bwteen production parts, repeatably.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dicer]

The way I read your first post is, "before and after engine testing". So I understand that as meaning, it is not a production environment, it is an experimental environment.
The other methods mentioned such as airgauging etc are good for a production setting. But in the experimental setting you would want accurate information on the internal profile, and the best way to achieve that is with a CMM. Anything else as mentioned is just an old shop mechanics way of checking the bores. If this is done for a small quicky engine shop then go with any old standard way of measurement. But if this is a large OEM then use something that is going to give accurate data.