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Is this bottom skin heat/discoloration normal?

jcarne

Well Known Member
Patron
Hello everyone, fresh 4.3 hours on the aircraft and today I noticed the bottom skin has some discoloring from heat of the exhaust/exit cooling. I would think it would have to get pretty hot to discolor the aluminum like that. Is this normal? Anything I should do to try and make it better?

CHTs have been around 350-380 and I have been keeping the EGTs around 1300.

Capture by Jereme Carne, on Flickr

Thanks for the feedback!
 
I doubt the discoloration is from heat, especially that far aft. Looks more like a chemical reaction between the aluminum and some chemical. Possibly a detergent of some type that was not rinsed off thoroughly.
 
Breakin oil

During break in you are burning a lot of oil. If it is hitting the exhaust pipe, it is probably smoking a little bit. You might be even leaving a trail??
 
Thanks for the replies everyone, I went back out to the airport and did some more rubbing and it is definitely burned oil/combustion product. I guess I didn't rub hard enough the first time but it easily comes off.

Now the hard part of knowing when my engine is broken in... I have only burned 0.75 qts in those 4.3 hours. That also could have been the engine dropping some to get down to it's happy spot. Time will tell I guess.
 
the belly of my 7 looks the same, nothing to worry. your oil consumption seems to be normal for break in. my engine with nickel cylinders had used around 1 qt per 1 hour at the beginning. now it stabilized at 1 qt for 7 hours.

just keep track of your oil usage over engine/flight time, if it doesn't change anymore your're done.

btw... Congratulations to your First Flight!!!!!!!! i love the paint scheme of your wings. mine is the same. :)
 
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the belly of my 7 looks the same, nothing to worry. your oil consumption seems to be normal for break in. my engine with nickel cylinders had used around 1 qt per 1 hour at the beginning. now it stabilized at 1 qt for 7 hours.

just keep track of your oil usage over engine/flight time, if it doesn't change anymore your're done.

btw... Congratulations to your First Flight!!!!!!!! i love the paint scheme of your wings. mine is the same. :)

Haha thanks! Glad I'm not the only one that found flying more important than wiping that stuff off. lol
 
looks normal/accetable to me.
interesting that the "stain" is so far back... residues are either close to the exhaust or then tend to spread evenly in the very aft area.
by the way, we clean the exhaust stains with WD40, which seems a bit counter intuitive but works really well.
 
BTW, Simple Green Aviation mixed to a 1:3 ratio works wonderfully on removing all of the residue with little scrubbing.
 
BTW, Simple Green Aviation mixed to a 1:3 ratio works wonderfully on removing all of the residue with little scrubbing.

+1. I also use a pump sprayer with 10:1 Simple Green Aviation that works quite well if you give it a few minutes to soak.
 
Once, many, many years ago, I saw the exact same pattern on a SR-71. Just saying.........
 
BTW, Simple Green Aviation mixed to a 1:3 ratio works wonderfully on removing all of the residue with little scrubbing.

Thanks for the tip, it just so happens I need to order some more oil from Spruce, I'll add this to the list.

looks like friction heat from flying too fast!:eek:

Tom

hahaha

Once, many, many years ago, I saw the exact same pattern on a SR-71. Just saying.........

bahahaha nice one
 
I have 5.1 hours on my -9A. Lycon IO 320, I've used about 1 qt, the belly got
a little oily, but it wasn't burnt. CHTs are about 370-380, and I think the plugs are slightly fouled from running full rich.
 
I have 5.1 hours on my -9A. Lycon IO 320, I've used about 1 qt, the belly got
a little oily, but it wasn't burnt. CHTs are about 370-380, and I think the plugs are slightly fouled from running full rich.

Very nice, I haven't looked at my plugs yet but my IO-360 has only used 0.75 qts in 6 hours. My CHTs are about where yours are too.
 
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