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Spark plug blowout after Takeoff

s24789

Well Known Member
Patron
Wondering if anyone else has had this issue. To be fair I have not contacted Emagair as of yet. We replace our auto spark plugs at every condition inspection and reuse the short reach adapters.

We have about 4 hours on the plane since the inspection. Taking off on runway 07 I made an aggressive low level turn to crosswind and was climbing thru 300 ft Agl when we heard a loud bang and rough running engine. We immediately told the tower we were returning and landed on runway 25 twenty knots fast in airspeed and with 15 knots on the tail. All worked out OK. The analyzer told us the issue was with number 4.

When we pulled to top cowl the problem was obvious - the plug and short reach adapter were hanging by the lead. Further examination showed that 75% of the first three threads of the adapter were missing.

Has anyone had this same experience ? We of course blamed ourselves thinking we missed torquing the number four assembly but I am questioning that now. Due to the cost of the adapters, 100 bucks for 4 we have been reusing them. We are now thinking about replacing them at every other annual.

Thoughts ?
 
Yes, i have had an adapter blow out in flight. I switched over to steal adapters, however not comfortable with that back to aviation plugs.
 
I had an adapter crack while I was installing it. I did not over torque it but I did feel something give a little. I didn't like what I felt so I removed the spark plug - half of the adapter came with it:eek:

I feel certain that if I had gone for a flight I would have had the same experience that you reported.

I replaced all 4 adapters that were like the one that broke. Even though I was running a Pmag at the time, I bought the new Lightspeed adapters from ACS. At bit more expensive but higher quality.

P.S. I'm not a fan of LSE ignitions but they do make high quality adapters.
 
from a mechanical perspective, is it better or worse to have multiple threaded connections under cycling pressure loads?
 
Further examination showed that 75% of the first three threads of the adapter were missing.

Check the other undamaged adapters to see how many threads are engaged when they are properly torqued. All engaged threads would be damaged during the blowout event so the fact that only three were damaged suggests that the adapter was not fully threaded into the cylinder head.

Erich
 
Properly made and installed adapters are well proven. Andy Findlay's Reno racer uses auto plugs and adapters at 90+ inches of manifold pressure with cylinder pressures about triple what an atmo engine runs.

Be sure you thread the plug into the adapter first, then torque the plug into the head to the specified value, then torque the adapter hex to the specified value.
 
Check the other undamaged adapters to see how many threads are engaged when they are properly torqued. All engaged threads would be damaged during the blowout event so the fact that only three were damaged suggests that the adapter was not fully threaded into the cylinder head.

Erich

+1

When installing plugs, the pMag instruction say to torque the plug and adapter as an assembly. Over the years I found a couple of adapters that were binding on install - to the point normal torque was not adequate for seating. This can happen from inadvertently cross threading at some point along the way or anything else that might damage the threads.

Recommendations:
- Assemble the plug and adapter first (as in a vice) fully seating the plug in the adapter. Check for smooth thread engagement as you do this.
- When installing the assembly, make sure the adapter goes in smooth, then torque. If not, replace the adapter.

Keep a couple of spare adapters on the bench and replace any that you suspect.

Carl
 
The threads on the adapters do erode over time. The innermost threads on mine were getting very pitted after maybe 12 years and 800 hours, so I replaced them with the LSE ones. For 14 years, I have applied anti-seize and torqued the adapters to 25 ft-lbs and then the plugs to 15 ft-lbs, as per the previous LSE recommendations. Their current recommendations are 35-45 for the adapters, 20 for the plugs. To each their own.

Edit: I have found also what Carl noted in the previous post - as the adapter threads become pitted, they are difficult to thread back into the cylinder. I will replace them upon the first sign of boogered threads.
 
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Do you guys chase the threads in the head to remove carbon? I do regularly for my massive plugs. (M1B)

Recently a friend did his wobble/ream and one adapter had a lot of cooked hydrocarbon products that made the adapter have high torque for removal.
 
Another question along those lines. When I installed my auto plugs, I torqued the plug and the adapter as one unit. During the annual, some of the plugs and adaptors came out as one and on others, the adapter stayed in the head.

Is it OK to just put the new plug back into the well seated adapter and just retorque?
 
I have had an emagair adapter break during install. Good chance I over torqued it. However, I have since compared the suggested adapters for lightspeed ignition with the emag adapter. The lightspeed require a much higher torque value and are more sturdy. If you plan to replace yours you may look there.
 
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lucky some days

Had an adapter break in half on plug removal. Darn. Lucky for me the Snap On truck was near the hangar. "Hey, you got an easy out that is THIS big?"
Yup, part of an expensive kit. Can I buy just that one?
Well, ok... because Snap On has a reputation. Good guys!!!
 
Another question along those lines. When I installed my auto plugs, I torqued the plug and the adapter as one unit. During the annual, some of the plugs and adaptors came out as one and on others, the adapter stayed in the head.

Is it OK to just put the new plug back into the well seated adapter and just retorque?

That happened to me too, last plug change. My mechanic recommended removing all the adapters, lightly brushing the threads, sparingly apply an anti-seize, then torquing the adapters in separately to 20 ft-lbs, then the plugs in to 18 ft-lbs. I note that Emag recommends against installing the adapters separately, saying it can overstress the adapter neck and lead to breakage while installing the adapter.
 
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Another question along those lines. When I installed my auto plugs, I torqued the plug and the adapter as one unit. During the annual, some of the plugs and adaptors came out as one and on others, the adapter stayed in the head.

Is it OK to just put the new plug back into the well seated adapter and just retorque?

I installed my LSI adapters once, and remove ONLY the plugs during maintenance. I followed LSI original instructions. In your case, it sounds like you did not torque the adapter properly. You are under torqueing the adapter or over torqueing the plug. Properly installed adapters should not need to be removed from the head to service the plug.

........... This is what I do........... As always, follow the instructions from your supplier until proven wrong.

Just to be clear, Always have a plug in the adapter (snug) before installing or removing adapters from the head.
 
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This is where the Lightspeed manual and pmag manual differ. I suspect that the specs on the different adapters is why.

Pmag says:

“Auto Spark Plug Adapters - Plug adapters permit the use
of 14mm automotive type plugs. Use short reach (SR)
adapters if your aviation plug callout is “M” type (for
example REMXXXX). Use long reach adapters (LR) if
your aviation plug callout is “B” type (REBXXXX). First,
install adapters with the supplied gasket on the spark plugs
finger tight. Then, insert the combined assembly (plug with adapter) in the engine and tighten to 18 ft/lb (standard auto plug torque) through the spark plug ONLY. Do not torque the adapter itself.”

Lightspeed says:

“ Install adaptors in cylinder head using the supplied copper washer. Torque to 35 - 45 ft-lbs using anti-seize compound.
• Install automotive style spark plugs with their washer. Torque to 20 ft-lbs using anti-seize compound.
* WARNING- DO NOT USE SHORT REACH ADAPTERS IN ENGINES THAT USE LONG REACH AIRCRAFT PLUGS OR VICE VERSA.”


I installed my LSI adapters once, and remove ONLY the plugs during maintenance. I followed LSI original instructions. In your case, it sounds like you did not torque the adapter properly. You are under torqueing the adapter or over torqueing the plug. Properly installed adapters should not need to be removed from the head to service the plug.

........... This is what I do........... As always, follow the instructions from your supplier until proven wrong.
 
The threads on the adapters do erode over time. The innermost threads on mine were getting very pitted after maybe 12 years and 800 hours, so I replaced them with the LSE ones. For 14 years, I have applied anti-seize and torqued the adapters to 25 ft-lbs and then the plugs to 15 ft-lbs, as per the previous LSE recommendations. Their current recommendations are 35-45 for the adapters, 20 for the plugs. To each their own.

These are the original instructions that I follow.
 
where you would expect the thread to fail is the inner ID of the cut thread adapter since it is a smaller diameter thus less thread contact area. however, there is less pressure area at the ID so the failure position could actually be the OD of the adapter thread. I'm glad these guys made it back OK.
 
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I installed my LSI adapters once, and remove ONLY the plugs during maintenance. I followed LSI original instructions. In your case, it sounds like you did not torque the adapter properly. You are under torqueing the adapter or over torqueing the plug. Properly installed adapters should not need to be removed from the head to service the plug.

........... This is what I do........... As always, follow the instructions from your supplier until proven wrong.

Just to be clear, Always have a plug in the adapter (snug) before installing or removing adapters from the head.

My EFII instructions state to put the adapter on the plug and torque as a unit. Followed my instructions to the tee. Contacted Robert and he stated to put the plug back in and retorque to spec.
 
This doesn't necessarily have anything to do with how the adapters are installed. It may just be a choice of material issue.

Brass comes in many forms. Yield strength ranges from ~5K to ~100K psi. Common "free machining" brass is loaded with lead, and yield is only about 20K. Cartridge brass and yellow brass are both more like 40K. Just examples; you get the idea. It might be worth asking your vendor what they specified.
 
Discussion has been for LSE and pMag adapters. What about the brass adapters that come with the SDS kits? SDS installation instructions says to install adapter (no anti seize) at 30 ft lbs and then install spark plugs (no anti seize) at 20 ft lbs.

I have never removed my SDS supplied adapters even though each year I replace the plugs. Should I pull the adapters each year with the plugs and reinstall and torque with plugs installed in the adapter? Also, last annual I noticed I, for some reason I can’t remember, written in my condition inspection notes a different torque for the adapters than is what is in the SDS installation. I have 25 ft lbs for adapters and 18 for plugs. What is proper torque for the brass adapters?
 
Discussion has been for LSE and pMag adapters. What about the brass adapters that come with the SDS kits? SDS installation instructions says to install adapter (no anti seize) at 30 ft lbs and then install spark plugs (no anti seize) at 20 ft lbs.

I have never removed my SDS supplied adapters even though each year I replace the plugs. Should I pull the adapters each year with the plugs and reinstall and torque with plugs installed in the adapter? Also, last annual I noticed I, for some reason I can’t remember, written in my condition inspection notes a different torque for the adapters than is what is in the SDS installation. I have 25 ft lbs for adapters and 18 for plugs. What is proper torque for the brass adapters?

My Dad taught me to put anti-seize compound on everything, and I did -- until I read this blurb (https://ngksparkplugs.com/en/resources/5-things-you-should-know-about-spark-plugs);

Now I feel confused, hurt and betrayed; like discovering there's no Santa Claus or Easter Bunny...

I've always installed the inserts and then the spark plugs and then torqued the inserts down to 35lb/ft, and the plugs to 15lb/ft.

I believe the intent is to just to IRAN the plugs; if they are torqued to the same value as the insert, you'll pull the insert along with it...

*edit* The magic torque numbers come from the cyl. manufacturer -- republished in Champion's spark plug guide available @ https://www.championaerospace.com/wp-content/uploads/2015/06/AV6-R-Aug20141.pdf
18mm:
Lycoming 35ft/lb
Continental 25-30ft/lb
14mm:
all 25-30 ft/lb
 
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Discussion has been for LSE and pMag adapters. What about the brass adapters that come with the SDS kits? SDS installation instructions says to install adapter (no anti seize) at 30 ft lbs and then install spark plugs (no anti seize) at 20 ft lbs.

I have never removed my SDS supplied adapters even though each year I replace the plugs. Should I pull the adapters each year with the plugs and reinstall and torque with plugs installed in the adapter? Also, last annual I noticed I, for some reason I can’t remember, written in my condition inspection notes a different torque for the adapters than is what is in the SDS installation. I have 25 ft lbs for adapters and 18 for plugs. What is proper torque for the brass adapters?

This is the procedure we recommend for our adapters from the April 26 2019 SB:

1. Thread the spark plug into the adapter
2. Torque the assembly into the cylinder head using the PLUG hex to 19 ft./lbs.
3. Torque the ADAPTER further to 25 ft./lbs. Use only a thin stripe of anti-seize compound on the plug and adapter. Do not coat the threads.
 
Yes the copper gasket was installed. Thanks for the great discussion. Waiting for a new harness and we will test fly the plane.
 
you could drill a small hole in the adapter and put a thermocouple in it to determine the operating temperature. heat will not transfer out of the adapter thru the threads as if it were solid material because of the reduced thread contact area. find a material that will maintain it's strength well above the highest operating temperature. for threads, consider a stress concentration factor Kt of at least 4 when evaluating the stress capability of the material. my guess is the adapters get smokin hot. for critical engine hardware, have someone show you the data and the analysis. you want a lot of stress margin for a part like this... not hanging by a thread.
 
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The annealing temp for brass is 800-1000F generally. No way it gets anywhere close to this in this application.

Tens of thousands of brass adapters flying successfully, some in applications much more stressful thermally than in your average day to day Lycoming.

Look to thread damage in the heads or adapters or improper installation for the cause of failure rather than the material.
 
The annealing temp for brass is 800-1000F generally. No way it gets anywhere close to this in this application.

Tens of thousands of brass adapters flying successfully, some in applications much more stressful thermally than in your average day to day Lycoming.

Look to thread damage in the heads or adapters or improper installation for the cause of failure rather than the material.

any data or analysis results? you know, the basics... adapter max operating temperature, fatigue properties of the material at temperature, stress condition upon installation, operating stress condition at temperature.
 
The CHT sensor is located about 1.25 inches away from the spark plug boss. Safe to say it is close to representative of the temperature of that area in an aluminum head.

Strength of brass isn't significantly lower at the typical 300-400F (150-200C) temps seen here. Also, if the material was not up to the task, you'd see a high failure rate for all adapters in service, which we don't.
 

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the adapter is insulated from the head by the limited contact area of the threads. you really don't know the adapter temperature unless you measure it. the temperature of the adapter will be hottest at the flame end and cooler at the top.

ppt2.png
 
Your depiction above is not representative of the adapter design. The adapter also has a large flat area on top with a copper washer touching a flat area on the head. The adapter will be close to the same temperature of the head in my experience. The major area of exposed surface is to the aluminum head, rather than the combustion chamber.

If you can find a way to accurately measure the temp at the middle of the threads I'd be interested in seeing the results.

You seem to be theorizing that the adapters run too hot for the material here and they are yielding. If so, that would be systemic and most would be failing. That's not the case at all. I've sold thousands of these and most that I replaced for customers were over torqued on installation and/or by not following the revised installation procedure I posted earlier.

Aluminum isn't suitable for use here due to the rapid drop off of strength at these temps. Stainless has very poor thermal conductivity so the plug firing end runs too hot. Plain steel also has rather poor thermal conductivity and can corrode into place over time.

That leaves brass which has decent TC, decent strength at these temps and doesn't seize into the aluminum or steel plug threads easily.
 
drill a small hole in the top of the adapter and insert a thermocouple, then go fly and read the max temperature. a 2D thermal analysis can determine the temperatures of the adapter elsewhere.
 
I'd guess a ring CHT probe would also give a pretty good idea of the temperature of the adapter, at least at the top.
 
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