Spark plug gap DIY

txflyer

txflyer

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O.k. So I got 12 brand new Tempest spark plugs in (massive) and the first one out of the gate I notice the gap is smaller than .016 on one of the electrodes.

TCM and Tempest recommend between .016 to .021 for the UHRM40E for my Continental 0-470-R.

There is reams of information about narrowing the gap with a gap tool, but I see no information about widening the gap? Is there a tool for that? Or how do you do it? Safely that is ... thanks in advance... :)
 
It should come from the factory with a minimum of .016... Unless it was dropped, I would call Tempest and give them a heads up on a manufacturing issue..
 
N801BH said:
It should come from the factory with a minimum of .016... Unless it was dropped, I would call Tempest and give them a heads up on a manufacturing issue..
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You'd think they would all come with a gap of .021 since that's the widest gap recommended.

It's no sweat to close the gap with a gap tool, but sketchy to widen them.

There is no 'gap widening tool' that I can find ... :dunno:
 
On auto spark plugs I have a little gap opener tool that allows you to pry the gap open. No idea if this is applicable to aircraft but I imagine a similar tool would work.

8e.jpg
 
tehmightypirate said:
On auto spark plugs I have a little gap opener tool that allows you to pry the gap open. No idea if this is applicable to aircraft but I imagine a similar tool would work.


Documentation specifically forbids prying against the electrode.

You can damage them (they say). :redface:
Click to expand...
 
txflyer said:
tehmightypirate said:
On auto spark plugs I have a little gap opener tool that allows you to pry the gap open. No idea if this is applicable to aircraft but I imagine a similar tool would work.


Documentation specifically forbids prying against the electrode.

You can damage them (they say). :redface:
Click to expand...

Yes you can damage them.....:yes::yes:
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I need to come up with a tool that will slide in between the ground electrodes and the center electrode that you can carefully screw apart.

But a tool with jaws less than .016 thick that will force the ground electrodes out, you'd need unobtanium or kryptonite .... :nonod:

I'm probably over-thinking this. I read one guy ground his out, sanded the ground electrode until he had the gap... :confused:
 
For reference, this is a picture of an iridium fine wire plug (left) and a massive plug (right).

198595_spark_plug_fine-wire_massive.jpg
 
tehmightypirate said:
On auto spark plugs I have a little gap opener tool that allows you to pry the gap open. No idea if this is applicable to aircraft but I imagine a similar tool would work.

8e.jpg
Click to expand...


On a used spark plug never use this tool. A used spark plug has high and low spots or ridges. If you use this style plug gaping tool the gap will be wider then what the gauge reads. This is why a good mechanic will use a wire spark plug gaping tool.

When plugs are made they come preset or gaped. The good companies put a cardboard sleeve in the box for the spark plug. This keeps the gap from changing do to the end of the sparkplug being hit on the end of the box in shipment.

You never change this gap more the a couple thousands. You want to keep the center electrode parallel to the top electrode. If you look at them from the side they should be parallel. If you do not keep them parallel the spark will jump the gap at the closest point and you do not get a good even flame front.

This is using an auto style plug. An aviation plug uses a complete different set of tools to check them.

Tony
 
txflyer said:
O.k. So I got 12 brand new Tempest spark plugs in (massive) and the first one out of the gate I notice the gap is smaller than .016 on one of the electrodes.

TCM and Tempest recommend between .016 to .021 for the UHRM40E for my Continental 0-470-R.

There is reams of information about narrowing the gap with a gap tool, but I see no information about widening the gap? Is there a tool for that? Or how do you do it? Safely that is ... thanks in advance... :)
Click to expand...

You have a gapping tool in your hand? See the slot? Grab the electrode with the slot down at the base in the big gap, not by the center electrode. Now bend out on it until it goes just past parallel with the core electrode and let is spring back to parallel. Parallel should give you the correct factory gap on a new plug, but of course, give it a check. Personally I run gaps on the open side, it's easier to stay smooth, lean, the wider you gap plugs. That's why cars had to go to HEI ignitions to get gaps big enough to assure ignition of the lean mixes for emissions. On my Lycomings I opened my upper gaps to .032 and had no problem firing them with my Bendix mags with mag drops balanced and in tolerance. The IO-470s I never did anything with because they leaned smoothly all the way to cut out.
 
Henning said:
You have a gapping tool in your hand? See the slot? Grab the electrode with the slot down at the base in the big gap, not by the center electrode. Now bend out on it until it goes just past parallel with the core electrode and let is spring back to parallel. Parallel should give you the correct factory gap on a new plug, but of course, give it a check. Personally I run gaps on the open side, it's easier to stay smooth, lean, the wider you gap plugs. That's why cars had to go to HEI ignitions to get gaps big enough to assure ignition of the lean mixes for emissions. On my Lycomings I opened my upper gaps to .032 and had no problem firing them with my Bendix mags with mag drops balanced and in tolerance. The IO-470s I never did anything with because they leaned smoothly all the way to cut out.
Click to expand...


I'll get Ron to show me tomorrow. I don't have any of the stuff with me at home right now.

I was thinking to run the gaps to .020 near the wide end of the scale since they're new plugs.

More gap means less fowling in theory.
 
There is a special tool for widening the gaps on massive aircraft plugs but it's a bit tricky to use. Bottom line is you shouldn't have to use any tool on a new plug straight out of the box.

Gap widening tool

12-51520.jpg
 
I think most mechs have made their own gap-widening tool which lifts up on the angled part where the side electrode attaches to the plug body. A gentle lift here hurts nothing. Anyone who has pushed side electrodes inward with the standard gapping tool to reduce that gap has at one time or another pushed a bit too far... or is inhumanly perfect.
Never put any pressure on the center electrode.
As the electrode wears, the gap widens. If you start with a wide gap, it could be out of spec soon so I have been putting them at the minimum gap specified.
 
1600vw said:
http://www.eaavideo.org/video.aspx?v=2050031304001
Click to expand...

In the video he explains the difference between automotive and aviation spark plugs. One difference being that aviation plugs are shielded to prevent interference with radios.

ROTAX engines use automotive plugs, but I have never heard of any radio problems.

Anyone know why there is no problem with the ROTAX using automotive plugs?
 
vintage cessna said:
In the video he explains the difference between automotive and aviation spark plugs. One difference being that aviation plugs are shielded to prevent interference with radios.

ROTAX engines use automotive plugs, but I have never heard of any radio problems.

Anyone know why there is no problem with the ROTAX using automotive plugs?
Click to expand...

Because most automotive plugs are resistor ones.... They surpress ignition noise....
If they didn't
your AM radio in your car would be filled with static...
 
vintage cessna said:
In the video he explains the difference between automotive and aviation spark plugs. One difference being that aviation plugs are shielded to prevent interference with radios.

ROTAX engines use automotive plugs, but I have never heard of any radio problems.

Anyone know why there is no problem with the ROTAX using automotive plugs?
Click to expand...

Because Rotax designed their engine(s) in the 1980-90 time frame when auto plugs had resistors. A resistor plug cuts AM noise down to below detectible levels in the LF AM broadcast band. In the VHF aircraft band(s) the noise is detectible but for all intents and purposes so far down in the grass as to not be noticeable.

In the late '50s resistor plugs for autos were available but fairly expensive. The alternative back then was to make the wire in the harness out of carbon-filled linen threads and that had its own set of problems, life of the harness being one of them.

Our engines were designed back in the 1930s era when neither resistor plugs OR resistive harnesses were much thought of. You just shut the engine off if you wanted to hear the Chicago Cubs game from Milwaukee.

Amateur radio operators running AM back in those days resorted to putting tin cans around their distributor/coil setups and running coax cable to their plugs. It was a lashup that you wouldn't exactly call airworthy but was good enough for your father's Buick.

You could run auto resistor plugs in your Lycontasaurus motor without a problem, but the FAA guy that was assigned to make that engineering change retired 50 years ago and was never replaced.

Jim
 
Silvaire said:
There is a special tool for widening the gaps on massive aircraft plugs but it's a bit tricky to use. Bottom line is you shouldn't have to use any tool on a new plug straight out of the box.

Gap widening tool

12-51520.jpg
Click to expand...

I never liked that one. I had a wire gauge set that had a slot tool that allowed you to grab the electrode at the base. Really simple to use with no risk to damaging anything.
 
There was another tool in the shop that had a thread that you ran the plug in one end, and on the other is mounted a threaded tube that has a thumb screw that looks like a an idle jet needle. What you did was thread the plug up in there so the needle would catch the edge of the electrode, then you kept turning to open the gap. PITA rig if you ask me, but it worked.
 
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Vice, punch, 5 lb hammer.
 
When I over shoot the gap I normally only do a thousands or two, I simply stroke a piece of emory paper thru the gap and call it good.

What is the failure criteria for a massive electrode plug?
 
N801BH said:
YUP....

That will work....:yes::yes:
Click to expand...

Yep, if you're carefull, you can always get the job done with more tool than you need, the inverse is not true. The cost of a mistake with too much tool is the part, the cost of a mistake with too little tool is typically a blood and skin sacrifice.:lol:
 
Oh, we could get fancy and give the radius in the electrode a tap or two with the TIG and then hit it with a squirt bottle about 7 seconds later, that'll tighten the radius and open the gap.
 
Henning said:
Yep, if you're carefull, you can always get the job done with more tool than you need, the inverse is not true. The cost of a mistake with too much tool is the part, the cost of a mistake with too little tool is typically a blood and skin sacrifice.:lol:
Click to expand...

You don't want to starve your inner Tim The Toolman Taylor. Using too much tool is good for the soul.

 
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Henning said:
I never liked that one. I had a wire gauge set that had a slot tool that allowed you to grab the electrode at the base. Really simple to use with no risk to damaging anything.
Click to expand...

Although it works it's not one of my favorite tools either. Because of that I hardly EVER (almost never) under-gap an electrode to avoid ever having to use it.
 
Silvaire said:
Although it works it's not one of my favorite tools either. Because of that I hardly EVER (almost never) under-gap an electrode to avoid ever having to use it.
Click to expand...

The only times I ever have to open them is after they've been dropped.
 
Henning said:
The only times I ever have to open them is after they've been dropped.
Click to expand...

I never have had to regap a dropped plug because they have always gone in the trash can. Just something I was taught early on.
 
Henning said:
You have a gapping tool in your hand? See the slot? Grab the electrode with the slot down at the base in the big gap, not by the center electrode. Now bend out on it until it goes just past parallel with the core electrode and let is spring back to parallel. Parallel should give you the correct factory gap on a new plug, but of course, give it a check. Personally I run gaps on the open side, it's easier to stay smooth, lean, the wider you gap plugs. That's why cars had to go to HEI ignitions to get gaps big enough to assure ignition of the lean mixes for emissions. On my Lycomings I opened my upper gaps to .032 and had no problem firing them with my Bendix mags with mag drops balanced and in tolerance. The IO-470s I never did anything with because they leaned smoothly all the way to cut out.
Click to expand...

I'm curious, what kind of life do you get from your mags and harness? Do you have any starting difficulty or other related problems? As I'm sure you are aware, electricity follows the path of least resistance. By opening up the spark plug gap, you are increasing the resistance on the system. The electricity wants to go to ground, and from what I understand, can start arcing across the distributor inside the mag or other places. Worn out insulation can allow the spark to go to ground also before it jumps across the plug.

I guess if you keep everything in tip top shape, the wider gap is less of an issue.
 
bgdriveway said:
I'm curious, what kind of life do you get from your mags and harness? Do you have any starting difficulty or other related problems? As I'm sure you are aware, electricity follows the path of least resistance. By opening up the spark plug gap, you are increasing the resistance on the system. The electricity wants to go to ground, and from what I understand, can start arcing across the distributor inside the mag or other places. Worn out insulation can allow the spark to go to ground also before it jumps across the plug.

I guess if you keep everything in tip top shape, the wider gap is less of an issue.
Click to expand...

Modern wires (even aircraft wires use modern insulators) I don't have any particular problems with. I am pretty pedantic about keeping my points adjusted and timing set as well as any graphite dust dust cleaned out of the distributor section. IME, if you're going to lose your spark plug to lower resistance, it's going to be through carbon tracks in the distributor.

I do this stuff every other oil change or so.
 
I have to take back what I said about the gap being off on the first new plug I pulled out of the box. I was using the wrong gauge.... :mad2:

All the new Tempest plugs I ordered gapped between .015 and .018. So I left them be and installed them.
 
vintage cessna said:
In the video he explains the difference between automotive and aviation spark plugs. One difference being that aviation plugs are shielded to prevent interference with radios.

ROTAX engines use automotive plugs, but I have never heard of any radio problems.

Anyone know why there is no problem with the ROTAX using automotive plugs?
Click to expand...


From my automotive past, I fully expect that there are radio suppressors inside the spark plug boot.
 
Fired up the plane yesterday, and she sounds good.

The new exhaust pipes and muffler helped cabin noise a bunch.

Looks like I got the gaps right and all the plugs torqued in and firing ... now for a flight test whenever this scud breaks.:)
 
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