Feeler gauge question

[milotrain]

I'm currently setting the valves on an engine project that I'm building and the specifications have prompted a question regarding the proper use of feeler gauges.

It seems like there are three different "modes" the feeler gauge can be in. Very Tight, I can pull the gauge out but can't get it back in. Tight, I can barely get it back in. Loose, I can easily get the gauge back in and take it out again.

My tolerance specification is to make sure the clearance is .008"-.009" so I have been setting things with a "Very Tight" .009".

My question is this: What, approximately, is the difference in inches between a loose, tight and very tight fitting. I'd assume that I can't really get any smaller a fitting than the gauge is thick as the gauge shouldn't be deforming. But perhaps it is. I do make sure once I set a very tight .009" that my .007" gauge is loose in the fitting, but I don't really have a good way of "proving" to myself what clearance I've actually hit. I've been thinking of getting a good micrometer and just test feeling my gauges so that I know what certain tolerances "feel" like.

Thanks for the help as always gentleman.

Milo

 

[Rayanth]

In the aerospace industry, we use the following rules of thumb:

If your maximum allowable tolerance is .009, then try and fit a .010 - if it fits, you're too big. If you have to struggle to jam a 10 in, you're good. You should never have to *force* a feeler gauge in, if you are forcing it, even if you eventually get it in, it's considered too big for the gap.

If a chosen feeler gauge is easy to slide in and out, with absolutely no resistance, then try the next size up. You should feel friction, but not enough to cause it to grab or bind the gauge. When you reach the 'snug but not binding or forcing it in point, that is your gap.

Bear in mind that if your surfaces are even slightly unparallel, your gap will vary from one side to the other.This may cause you to bind on one edge of your feeler gauge while the other is still loose, and give false readings.

- Ryan

 

[picclock]

FWIW when I measured my feeler gauge set with my best micrometer (20ths of a thou resolution) there was quite a wide variation in the sizes stated - in some cases well over a thou.

picclock

 

[doubleboost]

The way i was tought to set check valve clearance (bda twin cam solid lifters) if the clearance was ay 10 thou .
Use a 6 and a 4 together or a 6 and 5 as a no go
The thiner blade will bend and give you the required feel where a 10 thou blade will be stiff
Poor explination just use multiple blades to get the disired size
John

 

[Catminer]

Milo

Can you set up a dial indicator to check a valve you have set? Get a feel for your feelers.

Peter

 

[rake60]

Acquiring the "feel" for feeler gauges is very much like developing the "feel" for micrometers.

Cut yourself a little slack!

If .007 slips through easily and .009 hangs up bad, it's perfect!

Rick

 

[steamer]

I do make sure once I set a very tight .009" that my .007" gauge is loose in the fitting, but I don't really have a good way of "proving" to myself what clearance I've actually hit. I've been thinking of getting a good micrometer and just test feeling my gauges so that I know what certain tolerances "feel" like.






That's not a bad idea....As Rake said...this is the "Fingertip Technology" section of the art.

Practice practice...

Dave

 

[milotrain]

Thanks for the help guys! I learned two things since posting. One is that setting these valves too loose isn't really a problem, and the other is that they will tighten up a bit once you've run them in. So I guess I'm going to shoot for a little looser .009" feel than I've got.

I am still excited about getting a micrometer to feel it out, and I love that idea of using a thick blade and a thinner blade.

Thanks again.

 

[Rayanth]

Yif you trust your mill, you could also mill a two piece test block- one piece flat, the other withgrooves of varying depths on the mating side. Make the depths things you commonly see, like your 009, and then bolt the two together, forming channels out of the grooves. We have test blocks like this for our digital gap finders (interesting machines, but VERY expensive) but if your gaps are a good known value they can be good both for getting your feel, and for making shims of those thicknesses.

The two-piece method suggested is good, but it has a drawback. If you've been rough with your thin gauges and they get ANY kind of a kink in them, when stacked with another gauge you will very likely get a false feel for the gap. Additionally, if one gauge is out of tolerance, that's not a huge deal, but if both are, you're adding tolerance errors - never a good idea. I would still stick with a single gauge unless you just don't have one of the desired thickness.

- Ryan

 

[Tin Falcon]

I've been thinking of getting a good micrometer and just test feeling my gauges so that I know what certain tolerances "feel" like.

Well in this hobby you should have a good 1inch micrometer anyway. there has been much debate on "good" mitutoyo brown and sharp and srarrett are all top shelf but the imports accurate and adequate for most shops.
and as mentioned there is feel to mics as well.
but if you get a mic (get one that measures in tenths. .0001 resolution ) set it a couple tenths tight try to slip the gauge in set to size repeat seat a couple tenths loose . this will probably boost your confidence with feeler gauges. remember there are tolerances on everything nothing perfect.
and last but not least they do call thees feeler gauges for a reason
hope this helps.
Tin

 

[MachineTom]

First, setting the valve lash is not a trully exacting operation. The settings will change as the engine runs, valves elongate as they get hotter, Heads pushrods all expand different amounts due to material and temp differences. The lash is always changing while running.

Valve lash is to provide enough clearance so that the running gap between valve and follower is never "0" or less, when run at maximum temp and load. No need to overthink the lash settings.