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  #1  
Old 05-18-2021, 07:47 AM
s24789 s24789 is offline
 
Join Date: Jan 2009
Location: Hobe Sound, Florida
Posts: 302
Default Spark plug blowout after Takeoff

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 ?
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  #2  
Old 05-18-2021, 08:01 AM
FLTENG FLTENG is offline
 
Join Date: Jan 2005
Location: Victoria B.C. Can.
Posts: 380
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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.
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  #3  
Old 05-18-2021, 08:02 AM
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Rick_A Rick_A is offline
 
Join Date: Oct 2005
Location: Jacksonville, FL
Posts: 1,569
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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

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.
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  #4  
Old 05-18-2021, 08:15 AM
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Steve Melton Steve Melton is offline
 
Join Date: Apr 2011
Location: Cincinnati, OH
Posts: 3,425
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from a mechanical perspective, is it better or worse to have multiple threaded connections under cycling pressure loads?
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  #5  
Old 05-18-2021, 08:33 AM
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erich weaver erich weaver is offline
 
Join Date: Aug 2006
Location: santa barbara, CA
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Quote:
Originally Posted by s24789 View Post
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
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  #6  
Old 05-18-2021, 08:49 AM
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rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 6,093
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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.
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  #7  
Old 05-18-2021, 08:52 AM
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Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,179
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Quote:
Originally Posted by erich weaver View Post
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
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  #8  
Old 05-18-2021, 09:09 AM
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AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Ottertail, MN
Posts: 2,451
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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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Last edited by AlexPeterson : 05-18-2021 at 09:11 AM.
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  #9  
Old 05-18-2021, 09:22 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,220
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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.
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  #10  
Old 05-18-2021, 09:43 AM
219PB 219PB is offline
 
Join Date: Aug 2014
Location: Victoria, Tx
Posts: 515
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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?
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