[andrewbutler]

Hello All,

I recently had the the Christen inverted oil system in my RV7 EI-EEO, IO-360, MT 3 Blade CS prop tested for the first time in inverted flight. The aircraft has 100 hours.

Everything was perfect. When rolled back to normal flight, the oil pressure dropped significantly to around the 10 PSI mark. Prop sped up to 2700 and the power had to be retarded to avoid overspeed. The low power setting resulted in a gradual lost of height, and the pilot decided to pull a few high G manoeuvres with what was left of altitude before landing. When he did this, the Oil pressure came back up to normal. We figured that the ball bearings in the Christen Valve (the one on the firewall) had become stuck in "inverted" mode somehow and then had seated themselves correctly during he high g manoeuvres.

To check for possible engine damage and clean out the Christen Value, I changed and inspected the oil filter, pulled the Christen valve to check the innards and inspected the sump oil screen. All was perfect, except that the strainer contained two (relatively) large pieces of blue anodised strips of aluminum. They appeared to be identical in nature. My inspector reckons these are what caused the Oil pressure drop by interfering with with the seating of the large ball bearings in the Christen valve but has no clue what they might be and where they originated. When the blockage was cleared the pieces would have immediately passed into the sump to be captured by the Oil strainer. No other material of any kind was was present in the system.

See here for photos:

Has anyone got any idea where in my oil system these may have come from and are they swarf or are they functional?

Thanks for your help.

Andrew Butler
RV7 EI-EEO
Meath, Ireland,

 

[SmilingJack]

Looks like the threads off the AN fittings. I would double check for possible cross threading while it was installed.

Also, did you test for oil pressure twice? Or just once , then pull G's and pressure came back???

If you only went inverted once you should recheck the oil connections per install manual and make sure the bottom 2 hoses are NOT backwards.

Don't ask how I know this

 

[az_gila]

Looks like the threads off the AN fittings. I would double check for possible cross threading while it was installed.

...

I thought that too... but it doesn't seem like there is raw aluminum on the edges of the curly-cues. Also might be a bit wide for a single thread, which would also be expected to have a triangular cross section.

Perhaps off a badly made non-AN fitting we talked about a couple of years ago?

 

[Ron B.]

Could it be something that was part of a manufacturing process that didn't get discarded (i.e. AN fitting) and got stuck inside the part and got anodized. Looks like a shaving from machining process.
At first I thought it might be an AN seal but the pieces are longer than what a seal would be.

 

[rzbill]

I agree with the appearance of drill or lathe shavings that went thought the anodizing bath, hidden somewhere.

Are any of the oil system parts anodized the same color as these chips?

 

[az_gila]

Looks like they may have come from the inverted oil system.

A few of the parts seem to be custom machined from standard AN fittings -

 

[Ron B.]

az-gila, do these parts get anodized again after machining? Looks like no clean alum. visible on those shavings.

 

[andrewbutler]

az-gila, do these parts get anodized again after machining? Looks like no clean alum. visible on those shavings.

Yes, the T outflow fitting at the bottom left of the sump has an insert in it. The inside of the fitting would have had to have been widened a little for the insert to fit.... So a couple of burrs may have been left inside that when through an anodising process before being assembled. In the 100 hours the engine as been in operation, they could have been stuck in the valve the whole time or ideas? My sump is a Superior Cold induction type.

Here are some photos the fitting in situ during the build. The bottom hose goes to the Oil Strainer fitting on the bottom right, the centre to sump outflow on the bottom left.