REFLECTOR: Piston Crack -- Dye Penetrant Testing

[Bob Jackson via Reflector]

While checking the valves (with my new eBay Dental camera 'borescope'), I
happened to rotate it 180 degrees and noticed what appeared to be a crack in
the top of the #3 piston.  The valves looked great, but a piston crack is
scary.  The engine only has 75 hours on it and has not been abused
operationally.  The cylinders and pistons were brand new from Continental
(for our TNIO-550N).

 

Cyl-3_Piston_Before-2.jpg

 

  Cyl-3_Piston_Before-4.jpg  Cyl-3_Piston_Before-5.jpg

 

The lighter gray marks between the crack and piston part # in the photo is
where the top of the (plastic) dental camera hit the piston top when I was
looking at the valves.  Here's the #3 exhaust and intake valves.

 

Cyl-3_ExhaustValve-4.jpg  Cyl-3_ IntakeValve-1.jpg

 

After a few days of head scratching and worry, we used a small wire brush
and some AVGAS to clean off the top of the piston along the 'crack' line --
then took it out for an hour long flight (overhead the field at 6000').  I
wanted to see if the crack line would re-appear in the exact same spot or
not.  But after looking again after the test flight, there was no evidence
of any line in the 'after' video -- the top of the piston looked smooth and
clean where the stain/crack had been before.

 

My questions are:

.         has anyone seen similar 'crack's or 'oil tracks' on the tops of
pistons?

.         could it be a splash or 'seep' line of oil or fuel that appears
possibly just as the engine is shutting down?

.         has anyone ever done dye penetrant testing of pistons before
through the spark plug holes?

.         would the dye penetrant residuals likely damage anything or
contaminate the oil?

 

We're trying to gather some data and perspective before talking to
Continental and the rebuilder and would appreciate your comments or
suggestions.

 

Thanks,

Bob Jackson

Velocity XL/RG/XC

TNIO-550N

1000 hrs

N2XF

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