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Burned pistons and valve or normal?

bobmarkert

Well Known Member
My AeroSport IO-375 engine has 115 hours on it and I'm doing my first condition inspection. I bought a new borescope, and not sure if that was a good idea or not! The problem is I don't know what I'm looking at. Cylinders 1, 2 and 3, their pistons and valves all look the same. Number 4 piston looks different. Some sort of crusting,... Or worse yet layers of metal flaking off #4 piston. I sure would appreciate an education on what I'm looking at. That will determine if I'm going to have a good night sleep tonight or burn 8 gallons of stomach acid an hour!!!!!!!!........

The first two pictures are of #4 piston

Thank you in advance
Bob


#4 Piston


#4 Piston zoomed in


Piston #1


#1 piston edge. Looks scarry me


#1 cylinder valve
 
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I'm no expert, but I have borescoped cylinders that looked similar and opened them for no good reason other than the resulting education :)

To me, it looks typical for an engine running 100LL. If you opened the cylinder, you would realize that the flaky stuff is not aluminum, and if you cleaned it off, the piston would seem fairly pristine underneath.

My understanding is that the flaky stuff is a lead oxide and its possible to operate the engine in a way to make it more or less susceptible to forming. It's possible the variation between cylinders will cause it to form more readily in one cylinder.

Here's an article from shell about lead fouling:
http://www.shell.com/business-custo...entre/technical-talk/techart-18-30071600.html

For this selfish reason, I'm eager for a lead-free alternative to be readily available at airports :)
 
one more opinion

I'd suggest you get advice from other than the peanut gallery here......but real engine guys will no doubt be along in a minute.....
I'm curious, every time we see a borescope photo, all things bad are ....'lead'!!!

yes, it has its effects, but I've pulled apart way more auto engines than aircraft, and everything in them, even if they were run at 4500 rpm on a racetrack, was a thin crust of carbon and other crud, depending on how long it was idled, what temp it was when shutdown, etc. etc....it was NEVER lead, as we ran premium unleaded fuel.
the valve has a tiny hot spot, but as Mike Busch often says, run it, and look again. If it's gone, it was a piece of crud stuck to the seat, which burnt or dislodged and blew out. If it's bigger, then there's something else going on.

but again, just an armchair quarterback watching the show.

nice pics, what borescope, how much, and where from? :)
 
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Chris and Dan, thanks for your replies. I value them. I will now be able to sleep soundly tonight and will resume my stressing in the morning.
:)

Bob
 
I'm no expert, but I have borescoped cylinders that looked similar and opened them for no good reason other than the resulting education :)

To me, it looks typical for an engine running 100LL. If you opened the cylinder, you would realize that the flaky stuff is not aluminum, and if you cleaned it off, the piston would seem fairly pristine underneath.

My understanding is that the flaky stuff is a lead oxide and its possible to operate the engine in a way to make it more or less susceptible to forming. It's possible the variation between cylinders will cause it to form more readily in one cylinder.

Here's an article from shell about lead fouling:
http://www.shell.com/business-custo...entre/technical-talk/techart-18-30071600.html

For this selfish reason, I'm eager for a lead-free alternative to be readily available at airports :)

Me too.

Said education says you're looking at deposits.

Agree with all the above. Looks normal to me.
 
Looks normal to me also, but I think your looking at an intake valve. These rarely go bad so you want to see if you can get a view of the exhaust valve, which will be smaller and look much worse than the intake. That's also normal, you're looking for symmetry of color around the perimeter. It may look like a burned pizza, or have rings of color, but as long as it looks the same all around you're good.
When you see an area along the edge showing a different color that's when it's time to get excited.
If you want to experiment you can also watch the valve open and close, guide wear can be seen as sideways movement just as it closes on its seat.
Just go slow and careful knowing you'll crush your new toy if you try to get near TDC.
Tim Andres
 
Exhaust valve

Thanks Tim,
I'll look at it exhaust valve today and post a picture. Maybe I should just crushed my borescope at TDC and be over it!
:)

I made a mistake once of buying a combination oil dipstick and temperature probe for my Harley. I got concerned at how hot the oil was running. When I called the Harley dealer he said throw that probe away, ride your Harley, change your oil on time, and enjoy the ride!
Bob
 
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Looks normal to me also, but I think your looking at an intake valve. These rarely go bad so you want to see if you can get a view of the exhaust valve, which will be smaller and look much worse than the intake. That's also normal, you're looking for symmetry of color around the perimeter. It may look like a burned pizza, or have rings of color, but as long as it looks the same all around you're good.
When you see an area along the edge showing a different color that's when it's time to get excited.
If you want to experiment you can also watch the valve open and close, guide wear can be seen as sideways movement just as it closes on its seat.
Just go slow and careful knowing you'll crush your new toy if you try to get near TDC.
Tim Andres


Can someone talk about the markings on the cylinder surface. You can see the honing marks and then some perpendicular lines. Hard to tell if its scored but appears to be on top of the hone.

Also one corner of one piston appears like it might be wet.

Not sure if wizard mention hes using 1 qt in 5 hours

Cm
 
going flying

Here is a shot of the #1 exhaust valve. It looks good to me.
I appreciate the knowledge base on this forum and everyone's willingness to help. Based on what I've learned and the feedback here I have two things to say

"Clear Prop"
"Smoke ON"

 
What's the compression on Cylinder 4? If the valve is burned, wouldn't the compression be low?
 
Compression

Recently done with the engine warm:
79/80
I really wasn't too concerned about the valve, it was the crud on the piston.
Bob
 
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