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  #1  
Old 05-28-2019, 03:32 PM
Jake14 Jake14 is offline
 
Join Date: May 2014
Location: Seattle
Posts: 388
Default damaged spark plug

checking the plugs (Champion REB37E) on the IO 390 and noticed a broken insulator. No idea how or when it happened, it's never been dropped and mag checks seem normal. Just wondering how unusual or serious this may be, insofar as the ceramic debris in the engine etc...

Anyone have any experience with this?

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Last edited by Jake14 : 05-28-2019 at 03:38 PM.
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  #2  
Old 05-28-2019, 05:13 PM
lndwarrior lndwarrior is offline
 
Join Date: Mar 2015
Location: Cloverdale CA
Posts: 304
Default

That spark plug terminal is seriously "foot-balled" indicating significant wear. Looks like the plug may have died from old age.

Disclaimer - I am probably not the person to rely on for a professional opinion....
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  #3  
Old 05-28-2019, 07:29 PM
Boyd Birchler Boyd Birchler is offline
 
Join Date: Sep 2014
Location: IN
Posts: 254
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I doubt the erosion of the electrode is of any significance,you are allowed 50% wear, this plug is nowhere near that. Can not tell if it is in gap tolerance.

Sometimes the porcelain just developes a crack for no good reason. A detonation and/or pre-ignition event can break the insulator. If that was the reason, the combustion chamber will appear very clean. Most mild detonation events do no damage, but you need to bore scope the piston top and cylinder to make sure all is ok.

As to the piece damaging the engine,I have not seen any in my experience from rouge spark plug porcelain hitting the piston or damaging the valve seat (likely just crumbles to powder). I have seen a carb spray nozzle get sucked through and damage the exhaust valve seat.

Last edited by Boyd Birchler : 05-28-2019 at 07:42 PM.
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  #4  
Old 05-28-2019, 07:57 PM
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RV10inOz RV10inOz is offline
 
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Location: Brisbane Qld. Aust.
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It is likely that plug has had a drop at some time, and it does not have to be from a great height. Manufactured defect? Maybe.

In any case, glad you found it as that is the most likely cause for preignition events which cause you considerable grief.

Dont worry about the bit of ceramic.......it left the building long ago!
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  #5  
Old 05-29-2019, 05:56 AM
fixnflyguy fixnflyguy is offline
 
Join Date: Jan 2006
Location: Winston-Salem, N.C.
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Default Seen it happen

It happened to me a couple years ago. I have about 300 hrs. on my plugs, and I have never dropped them since removing from the box. In my particular case it caused an above normal mag drop during run-up, I did the cursory lean/full power clean out, and mag checked OK...took off and after a few minutes of flying,I got a slight roughness (enough to differentiate from normal) and did an RTF for further investigation. The broken piece was "trapped" buy the electrodes and floating around inside the plug. I have heard from others that have also had broken insulators, but never with the trapped piece that I had, which likely caused the intermittent shorting of the plug.
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  #6  
Old 05-29-2019, 06:24 AM
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Definitely running rich and oil soaked. The crack is the least of your concerns.
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  #7  
Old 05-29-2019, 08:14 AM
Boyd Birchler Boyd Birchler is offline
 
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Location: IN
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"Definitely running rich and oil soaked. The crack is the least of your concerns."

It looks oil fouled because a plug that is not firing cannot get hot enough to clean it self!
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  #8  
Old 05-29-2019, 01:42 PM
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Mycool Mycool is offline
 
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Location: West Hills, CA
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Default issues

The root cause is from hot starts! By not following a proper procedure to start a hot engine will cause the ceramic to weaken and crack.

As a flight instructor flying many different aircraft from many different locations, this issue is a common one from starting the engine the same whether its hot or cold.

When you dump cold fuel in a hot cylinder expansion/contraction happens.

This is my procedure to determine if a hot start is required and how to do it.

1. Determine if the engine oil (always available inside the cockpit) is hotter than outside air temp, if it is move to step #2. Fuel injected engines are always harder to start when hot.

2. Mixture out, throttle cracked 1/8"-1/2", and fuel pump on. Crank engine and as soon as it start igniting advance mixture in, then hand right back on the throttle.


Generally you only get one shot at this, so if you don't do it the first time you then need to prime engine, which is what your trying to avoid because priming engine puts COLD fuel right into the combustion/spark plug. And its this that's causes abnormal wear.
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  #9  
Old 05-29-2019, 01:50 PM
NewbRVator NewbRVator is offline
 
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Location: CA
Posts: 280
Default

Quote:
Originally Posted by Mycool View Post
The root cause is from hot starts! By not following a proper procedure to start a hot engine will cause the ceramic to weaken and crack.

As a flight instructor flying many different aircraft from many different locations, this issue is a common one from starting the engine the same whether its hot or cold.

When you dump cold fuel in a hot cylinder expansion/contraction happens.

This is my procedure to determine if a hot start is required and how to do it.

1. Determine if the engine oil (always available inside the cockpit) is hotter than outside air temp, if it is move to step #2. Fuel injected engines are always harder to start when hot.

2. Mixture out, throttle cracked 1/8"-1/2", and fuel pump on. Crank engine and as soon as it start igniting advance mixture in, then hand right back on the throttle.


Generally you only get one shot at this, so if you don't do it the first time you then need to prime engine, which is what your trying to avoid because priming engine puts COLD fuel right into the combustion/spark plug. And its this that's causes abnormal wear.
Wow. Thanks. It took me a looongggg time to almost figure out what you so succinctly elucidated. VAF rules!!!
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