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18mm Spark Plug Washer/Gasket Reuse

BillL

Well Known Member
This topic has come up in a few threads over the years (per a site search) and this post is to add to the knowledge.

Champion has a Technical Bulletin 95-11 that says a new copper gasket should always be used any time a plug is reinstalled.

Per a Tempest engineer (thanks Vlad) -they say the same thing.

Current specifications for the washers is hard to find, but the previous MS17840B showed the thickness as .081" + .004" , i.e. 0.077" minimum.

I have collected gaskets for a while as it seemed inefficient to process 8 in the middle of inspection. They were annealed, tumbled in a small rock tumbler and washed in a brightening solution. This removed all the scale, therefore clean and soft.

All 24 were measured for thickness, the Champion publication mentioned reuse could be "out of spec", so thought I would check.

They sorted to two clear batches. The 16 group measured .0791” (OK), the 8 pieces measured .0755 - clearly below spec.

The conclusion partly supports Champion and Tempest guidance - don't reuse them. But, it is clear that they can be reused once and remain within the MS17840B specification.

Record keeping would have to be good, or just put new in the later check them with a micrometer when a viable batch has been accumulated.

Update #1: I finally got a new batch of gaskets from Spruce. 11 gaskets were measured and the average was 0.08011" - - - it will be interesting to process some of these used and see how much thickness they lost. Maybe the lower (6 sigma) limit is being maintained to save money.

Update #2: A friends group of 100 gaskets was annealed, bead blasted, ultrasonic cleaned and measured. (about 20 min work) They all were .0784" or thicker.
 
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Thanks for the research Bill!
After annealing my first baggie of used washers I decided I was money ahead buying new ones and storing the old ones indefinitely….
 
Thanks for the research Bill!
After annealing my first baggie of used washers I decided I was money ahead buying new ones and storing the old ones indefinitely….

I have been doing the same, but ran across the rock polisher and decided to clean off the heat scale and check them out. The labor investment of using new is confirmed. Although, if the day comes that we need to use the old ones and now we know the limits. :)
 
0.0055 under nominal is 0.1397mm. Thread is 18-1.5, so the 0.0755 washer means the plug would screw in an additional 33.5 degrees.

0.0015 under minimum spec would be 9 degrees.

Why worry? Am I missing something?
 
0.0055 under nominal is 0.1397mm. Thread is 18-1.5, so the 0.0755 washer means the plug would screw in an additional 33.5 degrees.

0.0015 under minimum spec would be 9 degrees.

Why worry? Am I missing something?

I have my doubts that the plug mfg tolerance is tight enough to even worry about this. DOn't know the AV design, but with the PV cyl's, there is a lot of clearance between the plug and the piston at TDC. I have annealed these washers and re-used without any negative consequences. Just didn't think this was an area where a thou or two would make a difference.
 
Plug gaskets

I have my doubts that the plug mfg tolerance is tight enough to even worry about this. DOn't know the AV design, but with the PV cyl's, there is a lot of clearance between the plug and the piston at TDC. I have annealed these washers and re-used without any negative consequences. Just didn't think this was an area where a thou or two would make a difference.

I started my aviation mechanic career in the '70's. Yes, I'm that old. I learned from a mechanic that was a helicopter mechanic in the Korean War (remember that one?). To this day he was one of the best mechanics I have ever known and I learned more from him than I could have with multiple other mechanics. I have been using annealed gaskets since I first got into this business and have seen NO ill effects from using them. I have heard of one incident of a plug departing company with the cylinder (my flight instructor!:eek:) and that one had not been torqued properly. That was one of the warnings in the Champion letter.

I have read the above thread with some amusement as the plug protruding into the cylinder another .004 inches, the difference between a new and not new gasket, doesn't seem like it would make much difference in how the plug works. I read the Champion letter and am not certain the plugs themselves are built within a tolerance of .00? inches. And the cylinder plug opening is likely not built to that tolerance. The problem with an old gasket is it loses its elasticity, meaning it is heat-hardened and will not seal as effectively. Take a new gasket and bend it (it will flex some), then take a used one and it will not bend. Annealing, if done properly, helps to bring back some of that elasticity. And some of that "give" is likely to compensate for the cylinder plug opening and the shoulder of the plug itself being variable in its dimensional tolerances.

That said: I have asked many people from mechanics to pilots who do their own maintenance if they are aware there are TWO sides to a spark plug gasket: a flat side and a rounded side. Most were not aware there was a difference. The flat side goes against the cylinder; the rounded side goes against the plug. That asymmetry is maintained to some extent even after being used and annealed.

I do have a small stack of new gaskets that I swap out every 2-3 times the plugs are removed for whatever reason and reorder some when I am submitting an ACS order.

IMHO: I'm sure this might stir some pots. If you are uncomfortable annealing and reusing your gaskets, use new ones. Make sure they are oriented in the proper direction!;)
 
Annealing spark plug gaskets

Could you describe your annealing process?

Get a piece of welding rod (NOT arc welding!:eek::D! And not safety wire) or other thicker wire and put a bend in it enough to hold the gaskets without falling off. You don't want hot gaskets rolling across your work bench..! ;)Take your Bunson burner (LP torch) and heat the gaskets up so they are glowing orangeish. Immediately plunge the gaskets into cold water. I will scuff the residue off with a piece of Scotchbrite......Done!:)
 
Get a piece of welding rod (NOT arc welding!:eek::D! And not safety wire) or other thicker wire and put a bend in it enough to hold the gaskets without falling off. You don't want hot gaskets rolling across your work bench..! ;)Take your Bunson burner (LP torch) and heat the gaskets up so they are glowing orangeish. Immediately plunge the gaskets into cold water. I will scuff the residue off with a piece of Scotchbrite......Done!:)

Quenching isn't required to anneal copper. Let cool at room temp and you're fine. They cool quickly. I don't think quenching hurts anything though....
 
Annealing

Get a piece of welding rod (NOT arc welding!:eek::D! And not safety wire) or other thicker wire and put a bend in it enough to hold the gaskets without falling off. You don't want hot gaskets rolling across your work bench..! ;)Take your Bunson burner (LP torch) and heat the gaskets up so they are glowing orangeish. Immediately plunge the gaskets into cold water. I will scuff the residue off with a piece of Scotchbrite......Done!:)

I don't know anything about it but I though annealing involved heat and a gradual cool down. I thought a fast cool down would harden the metal. Like I said, I don't know.
I just buy new ones.
 
Annealing..........

Quenching isn't required to anneal copper. Let cool at room temp and you're fine. They cool quickly. I don't think quenching hurts anything though....

That was just the way I was taught. Thinking back, maybe it was to get them cooled down so we could get them back on the airplane as there were 3 other airplanes waiting for their annual....:p
 
I don't know anything about it but I though annealing involved heat and a gradual cool down. I thought a fast cool down would harden the metal. Like I said, I don't know.
I just buy new ones.

That rule only applies to metal with enough carbon to be hardenable. Annealing is always done with a slow cool down. quenching should only be used fo hardening operations. Not sure it matters with copper, but slow cooling results in finer particle arrangement. This may only apply to carbon based elements though, like steel and iron.

Many ways to anneal copper and aluminum, but easiest is to get a color stick for a temp just above the annealing temp and heat to color change. For Alum washers, I use a sharpie. It disappears at just the right temp.
 
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Annealing...

That rule only applies to metal with enough carbon to be hardenable. Annealing is always done with a slow cool down. quenching should only be used for hardening operations. Not sure it matters with copper, but slow cooling results in finer particle arrangement. This may only apply to carbon based elements though, like steel and iron.

That makes sense from a molecular level. The crystal rearrangement would need to be quickly arrested with quenching to cause hardening of the metal.

Next time I'm messing with copper gaskets, I'll try both ways and see if it has any affect on the mailability of the copper.

Many ways to anneal copper and aluminum, but easiest is to get a color stick for a temp just above the annealing temp and heat to color change. For Alum washers, I use a sharpie. It disappears at just the right temp.
That's a pretty cool thing to know....!
 
Just a quick note, while I have never had an issue with plug gaskets, if you ever have the need to replace copper gaskets in other applications, like banjo fittings, head gaskets, etc….I anneal them right out of the box. They can harden over time and not make a good seal, regardless of torque.
 
Quenching after heating to orange/red will keep them soft (annealed). We did this in A&P school. You could take a washer and bend it with your fingers after doing this.
 
Quenching after heating to orange/red will keep them soft (annealed). We did this in A&P school. You could take a washer and bend it with your fingers after doing this.

Maybe so, but it’s not necessarily. You can’t easily bend new ones with your fingers and they are just fine.
They take a temper by being exposed to cylinder heat over a period of time, or we wouldn’t need to worry about it at all.

Anyway,… nobody is hurting anything either way.
 
If they could get away with it, they would say buy a new engine each annual as they love to sell us more things and add to the the landfill.
 
Quenching

Quenching locks in the crystal structure that exists at the moment it is quenched. Air cooling allows the crystal structure to change some as the material cools. Cooling rate can influence what fraction of the material changes, and to what (iron has something like 13 different crystal structures that are possible)

For carbon steels, quenching locks in a crystal structure that is harder (and more brittle). For most steel, this is called martensite. Followed by tempering, some of the martensite is transformed to austenite, which is more ductile. Air cooling steel slowly will allow it to return to an annealed state - mostly ferrite I believe.

For copper and brass, quenching locks in the softest crystal structure. So quenching anneals the copper. Pure copper won't age-harden (no alloying element to precipitate out of the crystal) so allowing a room temperature cure will still lead to a soft crystal structure, but with some grain growth occurring, which is undesirable. Finer grain structure is less likely to propagate cracks.

The main issue to avoid when annealing is spending prolonged period at elevated temperature - this will cause accelerated grain growth. Just get it orange hot and quench it.

The hardening that has occurred in the washer/gasket that we are removing by annealing comes from work hardening, in this case from the combination of compression and hoop tension. I don't believe there are any temperature-related hardening processes for copper, only work hardening.
 
Thanks Steve. Most copper allows can be heat tempered but probably not at the temperature of a cylinder head. I made a poor assumption.

I think we killed this one!
 
A bag of 100 gaskets is $60 at ACS. That $.60 cents each. The cheapest thing about flying is the pilot....

-Marc
 
Just some facts, not precise recommendations . . .

0.0055 under nominal is 0.1397mm. Thread is 18-1.5, so the 0.0755 washer means the plug would screw in an additional 33.5 degrees.

0.0015 under minimum spec would be 9 degrees.

Why worry? Am I missing something?

I don't think you are missing anything nor should you worry. Regardless of the clocking, the plug will move into the cylinder equal to the thickness reduction.

I just came aware of the pub and had some washers to evaluate the accuracy of the assertion that they would be "out of spec" if reused. I am not sure if the thickness loss is from the heat scale or crush deformation, but suspect more due to scale.

Champion claimed that extension of the plug into the combustion chamber could lead to excessive plug temps and possibly a source of pre-ignition from excessive exposure of the bottom threads.

I have a plug print and will look at that tolerance to the thread end. But being a cast head and not machined on the combustion side, the variability of that aspect could be more than a fully machined part.

The facts would indicate that there is indeed a limit on the number of times the gaskets can be heated, cleaned and reused, but no comment on what that might be. Using the information given, one might take this on and post.

Could you describe your annealing process?

Like others, stick a wire horizontally in the vise, (a crochet hoop) bent with a lip so the flame does not blow them off. With 20 or so they will flop hack and forth as the MAPP gas torch heats them. After they are evenly reddish allow to cool. Quenching is ok, but more work. Nothing magic.

The washer is work hardened from yielding during installation of the plug.
 
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0.0055 under nominal is 0.1397mm. Thread is 18-1.5, so the 0.0755 washer means the plug would screw in an additional 33.5 degrees.

0.0015 under minimum spec would be 9 degrees.

Why worry? Am I missing something?

I have been heating and annealing them for 25-years. I toss them when the inside diameter does not fit over the spark plug threads.
 
A bag of 100 gaskets is $60 at ACS. That $.60 cents each. The cheapest thing about flying is the pilot....

-Marc

Anneal a penny, and you can dig in with your fingernails and hold it real tight....
 
If you do choose to anneal the copper spark plug gaskets, do not use a MAP torch. One afternoon I could not find my propane torch so I used my MAP torch...and promptly melted the gasket.
 
Flame-maker..........

I annealed my first today…needed a reason to get a new benzomatic torch

Perfect excuse! Welcome to the world of Conservative Maintenance! You will likely find they work just fine!

Oh, yeah: LP gas is plenty hot to get them warmed up. MAP: that's for welding things! See above post....!:eek::eek::rolleyes::eek:
 
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If you do choose to anneal the copper spark plug gaskets, do not use a MAP torch. One afternoon I could not find my propane torch so I used my MAP torch...and promptly melted the gasket.

I have been annealing gaskets for years, and never melted one by mistake. I did melt one once to see what it took. When the washer starts to look "white hot", you are real close to melting.

After annealing and cooling, I usually test the washer for softness by twisting it by hand, just to be sure.

YMMV
 
You can also anneal them in an oven on the self-cleaning cycle. Best to wash them first and maybe wait for spousal unit to be gone for a while.
 
You'll have to help us understand how to weld with MAPP.

It's entirely possible to weld with mapp gas but you need 02 to get the flame hot enough. Mapp is essentially acetylene but most torches are air/mapp and welding steel is beyond the heat range without an oxidizer. You can easily braze with air/mapp.

-Marc
 
It's entirely possible to weld with mapp gas but you need 02 to get the flame hot enough. Mapp is essentially acetylene but most torches are air/mapp and welding steel is beyond the heat range without an oxidizer. You can easily braze with air/mapp.

-Marc

I understand and have a decent amount of gas welding experience. Just didn't understand how you get MAPP without 02 to 3000* I thought it burns well under 1000* without O2
 
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With respect to annealing copper gaskets, I read a few years ago a scholarly treatise published by a PhD metallurgist. He was also a bonsai tree gardener. That was when I learned that specific hardness in copper wire is used to "train" bonsai branches into their gnarled shapes!

This gentleman's treatise went into far more depth than I could ever fathom but his conclusion was clearly stated in layman's terms.

In order for the crystal structure of copper to achieve anything other than the pure "Condition N" natural or normal structure it must be quenched at a rate in excess of one million degrees per second. In short, water or air quenching make zero difference in the ultimate crystalline structure of pure copper.

I've never water quenched spark plug gaskets following reading this scholarly paper. I've likewise never done anything more than wipe down the gaskets with a shop cloth before annealing and again following annealing while the gaskets are still warm. They always come out clean and, of course, soft and maleable.
 
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