REFLECTOR: Piston Crack -- Dye Penetrant Testing

[John Dibble via Reflector]

Looks like lead deposits.  Amazing how fast the lead builds up.  Can't 
wait for the lead-free avgas.

John

On 6/15/2015 9:12 AM, Bob Jackson via Reflector wrote:
>
> 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.jpgCyl-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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