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06-07-2015, 11:33 AM
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Join Date: Mar 2006
Location: SoCal
Posts: 626
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Possible detonation or FOD?
Yesterday in my post flight inspection I noticed my alternate air door (vertical sump FAB) departed the aircraft, screws and all! This lead me to pull the plugs for a FOD inspection. What I found does not look exactly like FOD to me but it has me wondering if I am leaning to the point of detonation. The erosion on the piston head has be concerned. I have posted two photos 1 for scale and the other a closeup of the erosion.
Here is the closeup
The engine has around 150hr SMOH w/chrome cylinders and using a quart every 6 hrs. Is this normal erosion?
__________________
JD
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RV-7 N314SY (KWHP)
IO-360-B1B
CANbus based trim/flaps and electrical
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06-07-2015, 12:09 PM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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I don't think its eroded. Looks like an oil burn patina from breakin with a 100LL crust on top that chipped off.
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06-07-2015, 12:29 PM
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Join Date: Mar 2006
Location: SoCal
Posts: 626
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Lead deposits
Yes, consider the lead deposits only as markers. Look between the deposits where you can see the top of the piston directly. It's the pitted surface on the piston, not the lead deposits that worry me.
__________________
JD
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RV-7 N314SY (KWHP)
IO-360-B1B
CANbus based trim/flaps and electrical
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06-07-2015, 03:46 PM
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Join Date: Jul 2013
Location: US
Posts: 2,245
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Quote:
Originally Posted by aerhed
I don't think its eroded. Looks like an oil burn patina from breakin with a 100LL crust on top that chipped off.
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For those of us new to looking at cylinders with scopes...which is which?
Is the light sort of whitish area lead deposit or the piston? |
06-07-2015, 04:20 PM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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The white stuff is lead. The dark area is oil burnt onto the piston. The pistons themselves often have a nubby surface that looks rough under a borescope. The only iffy spot I see is that gob on the edge at 4 oclock. Being rounded it looks eroded, but I bet its cooked oil.
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Actual repeat offender.
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06-07-2015, 06:31 PM
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Join Date: Oct 2005
Location: Vancouver, WA USA
Posts: 908
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If a screw went thru a cylinder you would know about right then, they don't run well at all with a screw floating around in a cylinder beating the heck out of everything including the spark plugs, (spark plugs look normal?) your photo looks totally normal to me..
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06-07-2015, 07:56 PM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,515
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Quote:
Originally Posted by Russ McCutcheon
If a screw went thru a cylinder you would know about right then, they don't run well at all with a screw floating around in a cylinder beating the heck out of everything including the spark plugs, (spark plugs look normal?) your photo looks totally normal to me..
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+1 Ditto (8 9 10)
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Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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06-09-2015, 12:22 PM
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Join Date: Mar 2006
Location: SoCal
Posts: 626
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Would this increase of decrease the danger
OK, looking for a simple change here. I have fabricated a new door for the alternate air and reenforced the ring in the bottom of the FAB.
It is easy to see this assembly is not only prone to failure once unlocked but also leaks a good deal of air.
Has anyone used red RTV to create a thin bond between the door edge and the frame (Fillet between door edge and mounting plate)?
It should seal the air leak, reduce the door vibration and make it more difficult to become unlatched but still be weak enough to shear when pulling the cable.
The danger comes in the RTV fillet. When it gets sheared by pulling the door open it is possible that some would get ingested (if both sides of the bond failed). Given its RTV, how much of a danger is this?
__________________
JD
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RV-7 N314SY (KWHP)
IO-360-B1B
CANbus based trim/flaps and electrical
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06-09-2015, 01:09 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,027
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Quote:
Originally Posted by jdeas
OK, looking for a simple change here. I have fabricated a new door for the alternate air and reenforced the ring in the bottom of the FAB.
It is easy to see this assembly is not only prone to failure once unlocked but also leaks a good deal of air.
Has anyone used red RTV to create a thin bond between the door edge and the frame (Fillet between door edge and mounting plate)?
It should seal the air leak, reduce the door vibration and make it more difficult to become unlatched but still be weak enough to shear when pulling the cable.
The danger comes in the RTV fillet. When it gets sheared by pulling the door open it is possible that some would get ingested (if both sides of the bond failed). Given its RTV, how much of a danger is this?
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RTV in any location that could get exposed to fuel (in this case fuel from a flooded engine, etc) is a bad idea. RTV will turn to moosh from fuel exposure.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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06-09-2015, 01:10 PM
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Super Moderator
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,624
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Dont do that
Fuel often runs down into the FAB, sometimes from overpriming. RTV is not fuel proof enough. It will get gummy and flake off and you will ingest it or perhaps even clog a jet.
You really want that door to open when and if it is needed, so I would be careful of putting anything there that could cause it to stick over the long haul.
Vic
__________________
 Vic Syracuse
Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
Kitplanes "Unairworthy" monthly feature
EAA Sport Aviation "Checkpoints" column
EAA Homebuilt Council Chair/member EAA BOD
Author "Pre-Buy Guide for Amateur-Built Aircraft"
www.Baselegaviation.com
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