Unusual Spark Plug Erosion

[Cyril Gibb]

I've sent this picture to Tempest to see if this is unusual or not:  5 of 8 plugs looked like this.  3 remaining were pristine.

All had normal light tan colouring before I cleaned them.

No evidence of pre-ignition with a borescope.  No EGT temperature runaways.  CHTs always below 400.

[MB65E]

How many hours? The BYs are great. However, They will not last nearly as long a a fine wire or normal plug.

the etching looks funny.

I don't make 200hrs... however, I never clean them, just replace. 

-Matt

[Cyril Gibb]

Just now, MB65E said:

How many hours? The BYs are great. However, They will not last nearly as long a a fine wire or normal plug.

the etching looks funny.

I don't make 200hrs... however, I never clean them, just replace. 

-Matt

300 hours.  It was the etching that caught our attention, in addition to 5 being etched and 3 without.

[N201MKTurbo]

I would say they are arcing to a place somewhere on the side of the outer electrodes instead of straight across the gap. If you have ever TIG welded and contaminated the electrode and had the arc come from some random place on the electrode instead of the tip. It would be interesting to put them in a spark plug tester and see what the arc looks like. 

A good cleaning will probably get them sparking right again.

[carusoam]

Were the top plugs the clean ones...?

How is the oil use?

PP thoughts only, but it looks like maybe some oil is being burnt on there?  And the threads look like some oil There as well?

Is There oil dripping out of the exhaust pipe?

Best regards,

-a-

[Cyril Gibb]

4 minutes ago, carusoam said:

Were the top plugs the clean ones...?

How is the oil use?

PP thoughts only, but it looks like maybe some oil is being burnt on there?  And the threads look like some oil There as well?

I didn't notice the erosion until after I cleaned the plugs so I don't know top or bottom, but 5 (out of 8) were eroded like the pictured one, so it had to be at least one top or bottom and at least 3 cylinders.  Gladys uses about a quart after 20 or so hours after an oil change, then another quart after the next 15.  Oil stays clean (fully transparent) for about 25 or 30 hours.  ( I run EXTREMELY lean on the ground and 50 DF LOP at cruise) Compressions remain at high 70's.

I took the plug picture after I had put anti-seize on the threads.... no oil.  It looks like oil is on the electrodes because of the bright sunshine I took the picture in.  The electrodes are dry and when I removed the plugs, they were all evenly coloured a light tan... perfect.

[carusoam]

Cyril,

Can you see any lot number and part number info anywhere?  Either printed directly on the plugs or in the logs?

That does look like a lot of erosion.  Having three plugs not do that, does appear that's something went afoul at the spark plug factory.

Will you have any oil analysis done before and during the time these plugs were in place?

Its possible that the material that sluffed off, left out the exhaust pipe. Oil analysis may not show anything related to the plugs...

Share a pic of one of the good ones for comparison...

PP thoughts only, I'm still not a mechanic...

Best regards,

-a-

[Cyril Gibb]

I'll see if there's any identification on the plugs when I replace them.  I don't want an electrode separating when we visit the US southwest in a few weeks.  I'll also respond if/when I get some info back from Tempest.