Check those oil screens boys

Sid Lambert · #1 11-09-2013, 07:47 AM

What I thought would be a normal 2 day condition inspection turned in to much more.

O-320 - 1025.9 Hours - #1 Cylinder - AirTech 8.5:1 Pistons

plehrke · #2 11-09-2013, 08:05 AM

How did you determine where to look for where the piece came from? You pull all the cylinders? I sure would not have thought that lower flange is very loaded.

Sid Lambert · #3 11-09-2013, 08:12 AM

We knew it was a piece of a piston fairly soon after I found it so I decided all of them need to come off. It happened to be the second one I pulled.

I'm at a loss as to what caused it. Someone suggested shock cooling.

BillL · #4 11-09-2013, 08:28 AM

Sid, can you post a picture of the top, and edge of your piston? Let's see of there was a slight erosion of the edges. Looking for possible indicators of preignition or incipient detonation. Not saying that is it, but it is something to check that might cause higher than normal cocking loads on the piston. A cocking load would might stresses to that area.

Also can you show the thrust and anti thrust sides of the skirt to see if there is uneven pressure loading too.

The skirts are loaded, from firing pressures against the bore. The ovality of the piston does tend to try and make it round again.

It appears to have some corrosion pitting on the piston pin and scratches on the skirt. Has this engine been parked for any length of time in it's history?

aerhed · #5 11-09-2013, 08:59 AM

The piston skirts demonstrate classic overheating. That's what scores them like that.

flyboy1963 · #6 11-09-2013, 10:14 AM

I'm also interested that you show the finger oil strainer from the sump....the one most guys either don't know exists, or don't bother checking at each oil change ( guilty of this also!)
Is this an example of chunks that are too big and heavy to be circulated, thus will never find their way to the main screen or filter?

Funny how the piston looks a bit like some we pulled from a small-block chevy .....after a season of running 5000 rpm at the oval track!

rocketbob · #7 11-09-2013, 10:27 AM

Damage like that usually only happens with some type of foreign object floating around the engine, like a nut or a washer. I have seen burnt Lycoming pistons and that one doesn't look like it was overheated. Check the case and look for pock marks which would indicate debris bouncing around.

Mike S · #8 11-09-2013, 10:30 AM

Quote:

Originally Posted by flyboy1963

I'm also interested that you show the finger oil strainer from the sump....the one most guys either don't know exists,

IIRC, this is an item that is required to be checked during annual.........

43xD.d

Each person performing an annual or 100 hour inspection shall inspect (where applicable) components of the engine and nacelle group as follows:

(1) Engine section - for visual evidence of excessive oil, fuel, or hydraulic leaks, and sources of such leaks.

(2) Studs and nuts - for improper torquing and obvious defects.

(3) Internal engine - for cylinder compression and for metal particles or foreign matter on screens and sump drain plugs. If there is weak cylinder compression, for improper internal condition and improper internal tolerances.

BillL · #9 11-09-2013, 11:35 AM

Quote:

Originally Posted by rocketbob

Damage like that usually only happens with some type of foreign object floating around the engine, like a nut or a washer. I have seen burnt Lycoming pistons and that one doesn't look like it was overheated. Check the case and look for pock marks which would indicate debris bouncing around.

Yeah, the coloring does not look to be out of range. The attention was to the fine scratches, not as cause, but further understanding the total system.

Bob are you thinking the FOD was due to pinching between he counterweights and the lower piston? There don't seem to be any pock marks visible in the single picture? Clearly it only takes one divit. The clearance between the piston and the crank group is outside my knowledge.

gasman · #10 11-09-2013, 11:55 AM

This screen, like the oil filter should be considered during your FWF installation. Route things away so these items can be serviced without too much interference.

I pointed this screen out to an RV4 builder/owner on my field....... he pulled it at his next inspection period.
He later told me that he would never pull that screen again.....