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Borescoping cylinders: "Gunk" on piston

Draker

Draker

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Engine's got about 160 hours on it. Whenever I stick a borescope in to have a look at the inside of the cylinder, the cylinder walls and the valves seem fine and clean, but the tops of the pistons all have what I can only describe as "white gunk" on them. I've seen other borescope pictures of engines much older than mine where the piston surface is a lot shinier and cleaner. Is this something to worry about? I must admit that when I look inside with a borescope, I'm not really sure what warning signs I'm looking for.
 

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Draker said:
Engine's got about 160 hours on it. Whenever I stick a borescope in to have a look at the inside of the cylinder, the cylinder walls and the valves seem fine and clean, but the tops of the pistons all have what I can only describe as "white gunk" on them. I've seen other borescope pictures of engines much older than mine where the piston surface is a lot shinier and cleaner. Is this something to worry about? I must admit that when I look inside with a borescope, I'm not really sure what warning signs I'm looking for.
Click to expand...
WRT your "white junk"
Google: what does lead on piston look like lycoming
 
Good to know. I'm still learning. I usually run about 25 degrees LOP in cruise, and aggressively lean on the ground while taxiing.
 
Does the material buildup on top of a piston modify the compression ratio? IIRC higher compression pistons are only very slightly "taller" than a lower compression piston.
Thanks.
 
I lean aggressively and my pistons look a lot like that. Savvy says they're fine.
 
That is not lead and it is not from running rich. Lead doesn’t stick to anything. It is deposits that come from additives in modern fuel. Pretty rare not to have deposits like this on a clean running engine that is not burning oil. You should absolutely not be concerned with these deposits. In all my years have never seen a shiny piston crown, excluding those running water injection and those only a few hours old.

Black deposits are a bit more concerning. They come from running too rich or burning oil.
 
Last edited:
wsquare said:
Does the material buildup on top of a piston modify the compression ratio? IIRC higher compression pistons are only very slightly "taller" than a lower compression piston.
Thanks.
Click to expand...
Not substantially, no, these deposits are usually about 1/16” thick.
 
Those pistons look only a little worse than mine - and mine hardly ever see lead. Completely normal from all the borescopes I've seen.
 
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