IO-360 oil pan modification

[MikeT]

I have an IO-360 A series engine and want to put a Christen inverted oil system on it. This is an angle valve, horizontal induction engine with the air plenum under the oil tank.
The paper work I have says "extended modification required", but doesn't explain what that is. The modification is for the oil pick-up for when the plane is right side up, and says an 812-1 weld on boss. The boss it calls out is only long enough for the pipe thread in it. If the weld on boss has to be in the middle of the oil pan, like the origional is, it would require a long enough boss to be welded to the floor of the oil pan, extend through the intake plenum, and be welded to the bottom of the plenum. Has anyone done this modification or had this done? Any information would help.

Thanks
Mike

[skybolt31]

The boss goes on the back of the sump, not on the bottom of it. There is an installation manual for the system that you really should have, tells exactly where to weld the boss, how to shorten the oil screen and install the plug at the end of it and how to run the hoses, how to troubleshoot etc... I am sure it is available from aviat or from Spruce as pn 05-20600 for $17.50.

Some of the pages are available here:

http://musclebiplane.org/htmlfile/invert.php#page1

[Kevin Horton]

Christen's instructions have you weld the pickup on the back of the oil sump. This creates a potential problem in that the IO-360-A series engine has a long oil sump, and the oil pickup for positive g flight will be at the back of the sump. If you put the nose down in a steep dive, then pull the power to idle at high speed, the discing drag from the prop will cause the oil to move to the front of the oil sump. The oil pickup will now be sucking air, and the oil pressure will go to zero. If you have a non-aerobatic constant speed prop the prop will go to fine pitch. High airspeed and fine pitch leads to high rpm. My engine hit almost 4,000 rpm. I scrapped the prop and had the engine opened up for inspection. This was a very expensive lesson.

After my event, I talked to my engine overhauler, and a local aerobatic Pitts pilot. Both were aware of other similar incidents with Christen inverted oil systems on IO-360-A series Lycomings. Based on the recommendation of my engine overhaul shop, I switched to an inverted oil pickup from Raven Aircraft. It is compatible with the Christen boss welded on the back of the oil sump, but the Raven pickup is longer, and it puts the oil pickup towards the middle of the oil sump, so it is much less likely to be sucking air if the oil has run to the front of the sump.

My recommendation is to put the oil pickup boss on the back of the oil sump, but to replace the Christen pickup with one from Raven Aircraft.