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Stuck a scope into each cylinder just to look around inside my new engine (built 2021, has been ground run 4 times, ~30 mins total, never flown, last run about a month ago) and saw something that seems like it should scare the hell out of me. What are those lightning-shaped spiderweb lines? I think they look scored/carved into the piston, like it's been etched and pitted. My partner says they look more like surface buildup. These only appear on Cyl1 (front right), but I may go back and look at the others more closely.

(ignore the long streak across the entire top of the piston, that was the borescope touching the surface)

Please tell me this is normal.

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  • Re: Scarring on piston?

    by » 10 months ago


    Hello Jason

    Please check the other pistons.  if this is a new engine they are run at the factory for about 30 to 60 minutes at the factory before shipment.  (hot tested)  I have never seen a new piston with that type of marking.  I have also never seen one that clean on the top of the piston.  Normally there will be a black appearance due to the run on auto fuel at the factory with EN 228 spec MOGAS. 

    Perhaps someone else has seen this before? 

    Cheers


    Thank you said by: Jason Fish

  • Re: Scarring on piston?

    by » 10 months ago


    I'm  with RW in not seeing any real issue on the piston head surface on a new engine.

    It looks more like a build up from running. I would double check the other cylinders and maybe pull the #1 cylinder head off to just make sure. That's  the only positive way to rule out any real issue. Sometimes the eyes and mind can play tricks on us.

    p.s.

    People have accidentally allowed debris into cylinders which will cause issues.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


    Thank you said by: Jason Fish

  • Re: Scarring on piston?

    by » 10 months ago


    Scoped the other cylinders. They all have similar patterns, most of which definitely look more like a raised buildup. I'm kinda wondering if it's related to whatever paint pen they used to mark the pistons, coupled with ground runs that can never hit operating temps. Normally that material would burn off, but it just can't. Totally speculating.

    But that cyl1 sure looks like pitting, and I definitely want to look. I know I'm not comfortable pulling a cylinder head off right now, but maybe after some reading...

    37345_2_2a 2023-09-05 21.18.33.jpg (You do not have access to download this file.)
    37345_2_2b 2023-09-05 21.18.55.jpg (You do not have access to download this file.)
    37345_2_2c 2023-09-05 21.20.54.jpg (You do not have access to download this file.)
    37345_2_4a 2023-09-05 21.30.14.jpg (You do not have access to download this file.)

  • Re: Scarring on piston?

    by » 10 months ago


    Hi Jason

    Thanks for getting pictures of the other pistons.  Given the magnification I know that it may look alarming however when I see the stampings of the pistons sizes it gives some focus on the markings and size.  Here is what I think.  

    The engines are run in at the factory using MOGAS and as such there are a lot of things in that mix that when you dry it out (storage) stays behind as varnish and tars.  The color appears to be just that, varnish.  Unlike AVGAS,  that has about 20% toluene in the mix,  varnish is always present after storage.  (think carb jet gummy bits and float bowl deposits)  The varnish will dry as we know and when it sits as a film it may not always stay bonded together.  The many lines formed are most likely deposited gums and tars from the fuel.  The bright ones are where I believe the varnish has shrunk and has caused a split in the film.  What i think you are seeing is the deposits coming apart in the piston dome and not damage on the actual dome.  

    Your bore looks good and I don't really see any signs of detonation.  Perhaps runs some nice AVGAS, with its cleaning ability of the toluene, give it a good warm up and check again.  I believe it will clear up.

    Cheers


    Thank you said by: Jason Fish

  • Re: Scarring on piston?

    by » 10 months ago


    I think it's  build up too.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


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