OT- Advantage, if any, of using wire gauges instead of feeler gauges

I recently purchased some spark plugs and the directions specifically stated to use wire gauges instead of "regular" feeler gauges to set the gap. I have never owned a wire feeler gauge and have been setting spark plug gaps for over fifty years (maybe wrong). I tried to find some good explanation on the internet for using wire gauges but could not find anything useful. What is the purpose for needing to use wire gauges. Thanks in advance.

IF the electrodes are worn to "cup and ball" shape the flat feeler gauge is going to give too small results.
IMO not hugely critical...

If you have been doing this over fifty years than your eyesight is probably as bad as mine. Get out the
old magnifying glass and look at the electrode. Old plugs just had square electrodes and a tab. Never plugs
use many types of geometry to improve spark and longevity. Most new types come with the afore mentioned cup
and ball or some such feature.

If spark plugs are excluded:

A wire type can (by feel) measure distances between two surfaces (and detect whether they are parallel) at any point it can be slid along their length but won't tell you if the surfaces are straight. They could be somewhat curved, wavy, etc, as long as they are parallel.

A leaf gauge will (by feel) measure the distance between two surfaces at one or more point(s) along their length but not necessarily along the entire length. The two surfaces can be non-parallel as long as they are the same distance apart as the feeler gauge thickness at one or more points.

But a leaf gauge might stand a better chance of telling you that one of the two surfaces is straight although not always. Depending on what one is trying to do, using both might be a good idea. Does this make any sense ?

Actually setting the gap with a feeler gauge will set the gap to a larger size in that case, not a smaller one. It will sit on the high points of both sides of the gap, but those high points may not be opposite each other. So the distance from high point on one to a lower point on the other will be greater than the feeler gauge size.

Since we are talking about three dimensional electrodes, even the wire gauges can have the same error. But it will probably be smaller. And If you file the gap first, then they will not be ball and socket shaped and either way should give accurate results.

As for how much difference it may make, you tell me.

MattiJ said:

IF the electrodes are worn to "cup and ball" shape the flat feeler gauge is going to give too small results.
IMO not hugely critical...

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Yes Randy that makes sense. I got it now. The feeler gauge would give an average reading where the wire gauge might indicate a contour. Not sure how much difference it's going to make these days. I changed a set of plugs on a Dodge Caravan not too long ago. It was running fine but I was in there and hadn't changed the plugs for 150k miles. The outside electrode was all but gone and still ran fine. I could only explain this to myself knowing the new high energy systems put out a gazillion volts. Thanks guys.

I bought a used 1985 Ford ranger right before getting married. It ran fine and drove home fine, including stopping for gas. Got home and parked it. It would not start the next day.
The rotor electrode had worn down to a nub. It sent the high voltage back into the electronic spark control and fried that. I had to replace the rotor and module. Needed a special tool to unbolt the module.
Ended up taking the old station wagon on the honeymoon to a cabin in the woods.
Bill D

The rotor was not a sheet of metal it was just a loop of wire so it burned clear through not just a bigger gap.

That's a good one Bill. It's amazing what you find sometimes. I have an F250 that started to get a slight shimmy when going around a right hand turn. I put it up on ramps and found that the I beam cross member in the suspension ( not sure what it is called but connects the drivers side suspension to the passenger side) was missing both bolts that connect it to the frame. Could have been bad.

crossthread said:

That's a good one Bill. It's amazing what you find sometimes. I have an F250 that started to get a slight shimmy when going around a right hand turn. I put it up on ramps and found that the I beam cross member in the suspension ( not sure what it is called but connects the drivers side suspension to the passenger side) was missing both bolts that connect it to the frame. Could have been bad.

Click to expand...

My first car was a 1974 Dodge Dart. Changing the oil I noticed one of the four bolts holding on the main K-member of the front suspension was missing. this was a 1" bolt!. I wonder if it was ever even installed at the factory.
Bill D