jdeas

jdeas

Well Known Member
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?
 
I don't think its eroded. Looks like an oil burn patina from breakin with a 100LL crust on top that chipped off.
 
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.
 
aerhed said:
I don't think its eroded. Looks like an oil burn patina from breakin with a 100LL crust on top that chipped off.
Click to expand...

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?
 
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.
 
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..
 
Russ McCutcheon said:
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..
Click to expand...

+1 Ditto (8 9 10)
 
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?
 
jdeas said:
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?
Click to expand...

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.
 
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
 
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