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Spark plugs abnormal wear

druidjaidan
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druidjaidan Collaborator

druidjaidan

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We took our plane up to a local MSC to have the 100hr AD's done, a few squawks taken care of, and other preventive maintenance.  We pulled the plugs to clean and gap them and found something my mechanic had never seen before.

The bottom plugs for cylinders 1, 2, and 3 look like they've been blown apart.  These plugs have about 250hours on them.

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Edited by druidjaidan
carusoam Grand Master

carusoam

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Youser!

Do tell... who made the spark plugs, what model are they?

Since they are the bottom plugs, what could make it only happen there?

I have not seen a plug shed parts before.  Not that I have much experience either...

Best regards,

-a-

Edited by carusoam
druidjaidan Collaborator

druidjaidan

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Tempest UREM38E.  I sent an email to a couple people listed as support contacts on the tempest site.  I'll see if they get back to me with their thoughts.

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cnoe Mentor

cnoe

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Did you stick a borescope in the holes yet to see what the pistons look like?


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cctsurf Proficient

cctsurf

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I agree somewhat with everything that has been suggested, borescope and download the CHT history, but I wonder about the metallurgy on the center electrodes.  Notice that the outer electrodes seem to be just fine.

druidjaidan Collaborator

druidjaidan

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Talked to the support rep at tempest.  His initial thought was that it was "failure to rotate the plugs".  He ended backtracking that pretty hard when I pointed out just how chucks appeared to be missing and told me to send a few plugs in for analysis.  We'll see.

As for temperatures.  It certainly possible, but the damage doesn't really resemble the examples I see online for any of the preignition or detonation.  The engine has been perfectly smooth running, and makes normal power.  All of which I wouldn't expect if something had been drastically wrong like that or a mistimed mag.  

Unfortunately we can't pull engine monitor history, we only have a JPI Scanner.  We've actually been more concerned about too cold than too hot since we bought the plane.  During the winter we struggle to make it to the green arc for CHT and the scanner reading 280-320, maybe getting to 360 during a long climb in the summer.  

Obviously something is happening or happened, we'll see what Tempest says when they get the plugs.

carusoam Grand Master

carusoam

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Having a plug dismantle itself like that is not normal wear.

It may not be the plugs fault.  The pictures of the other examples showing plug deterioration were caused by pre-ignition which is usually something else going on first.  Preignition is often preceded by high power and very hot CHTs.

Do you know what your max FF is at full throttle, during Take-off?

PP thoughts, not a mechanic...

Best regards,

-a-

 

carusoam Grand Master

carusoam

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Get a feel for the person you are sending your plug to.  Make sure you know the person's name to follow up with.

Its in everbody's interest that they don't accidentally lose your parts. Make sure you have every part number, lot number, serial number or any other number related to the plugs.  Both the good and the bad ones...

it would be interesting if the bad ones are from a different family as the good ones...

Best regards,

-a-

carusoam Grand Master

carusoam

Posted
Posted

Too high of an ignition timing >25°BTDC could be an initiator of 'detonation'

But that would also come with higher than normal CHTs...

Worth looking into to make sure everything is set up properly.

Best regards,

-a-

Shiny moose Proficient

Shiny moose

Posted
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I am normally just a lurker, but I would scope the cylinders, if the non steel ( piston, head) parts have not been distroyed due to improper combustion, heat. Then Look into the lot/ manufacturing date of those plugs, we might have more plug failures coming due to plug material not properly controlled

just my opinion , and very interested in what the plug manufacturer response is

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