Oil Drain Plug location on IO-360-A1B6D with Christen Inverted Oil system?

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m20r

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m20r
Changing oil on a Pitts S1 for the first time, not sure where the drain plug is. My mechanic said it is "A" in below picture, but A is part of hose that goes to the Christen Inverted Oil system. It looks more like "B" to me which is a screw on the side of oil pan (a little below the engine model/serial number plate). My mechanic said it is definitely not "C" which is the screw located in the middle of bottom of oil pan. Can anybody advise? "B" and "C" are very tight and before I use more brute force to try to loosen them I would very much appreciate any info from people with Lycoming IO360 engine. I remember on another IO-360 engine which had quick drain plug it was in the "B" location.

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But this is hardly specific to biplane, anybody who change oil on Lycoming IO-360 with inverted oil system (Decathlon, Extra, RV, ...) should know!
 
m20r said:
But this is hardly specific to biplane, anybody who change oil on Lycoming IO-360 with inverted oil system (Decathlon, Extra, RV, ...) should know!
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My Decathlon engine doesn't look anything like that. It has a fuel servo and air box on the bottom of the fuel sump. Drain should be at lowest point in pan. markup_1000005667.png
 
m20r said:
But this is hardly specific to biplane, anybody who change oil on Lycoming IO-360 with inverted oil system (Decathlon, Extra, RV, ...) should know!
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Not biplane specific, no, but a lot more people running inverted systems over there than here.
 
Go to Lycoming and download the parts manual for that specific variant of engine. The drawings will show the drain plug.

Location A is the suction screen. Looks like it has a T between the sump and hose, with a cap on the T. I think that cap would work to drain, and it probably is the low point in the system. So ... I think your mechanic is right.
 
"B" is an oil drain plug (parenthetically - it doesn't appear to be safetied on your engine). On Lycoming IO-360s it is not the lowest point on the casting. Photo of my IO-360-M1A below showing a quick drain installed on the Port drain location:

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You can also see a second drain plug in the same location on the Starboard side. As shown in the post above, for aerobatic engines the sump is modified with additional fittings for supplemental oil return.
 
Oops. That’s what I meant. That’s where mine is. I’m surprised an IO Lycoming doesn’t have one.

For the guys unfamiliar with forward facing servo sumps, there is no oil in the lower chamber of the sump. It’s partitioned off. Oil above, intake air below. When you hear reference to “cold air” sumps, there’s a physical separation between them so hot oil doesn’t warm the induction air.
 
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Stewartb said:
Oops. That’s what I meant. That’s where mine is. I’m surprised an IO Lycoming doesn’t have one.

For the guys unfamiliar with forward facing servo sumps, there is no oil in the lower chamber of the sump. It’s partitioned off. Oil above, intake air below. When you hear reference to “cold air” sumps, there’s a physical separation between them so hot oil doesn’t warm the induction air.m
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Here’a a pic to illustrate the insides of a Lycoming forward facing servo sump. In this case the oil drain is easy to see at the front right of the sump.
 

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Stewartb said:
Here’a a pic to illustrate the insides of a Lycoming forward facing servo sump. In this case the oil drain is easy to see at the front right of the sump.
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And here’s a Superior Air Parts cold air sump for comparison.
 

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One additional comment: the cap on the T at location A is lower than the drain plug at B, especially with the aircraft in 3 point stance. Wouldn't hurt to open both to get the maximum amount of sludge out. Some oil is going to pool in the hose and the suction screen housing.

Also, the suction screen at A is supposed to be checked for contaminants (metal) when you change the oil. A lot of owners and mechanics blow that off unless they find metal in the pressure screen or filter. It can be a bit finicky because of the crush gasket. The inverted system can make it even more of a PITA if the hose is stiff and has taken a set. My advice is buy a half dozen crush washers and get used to doing it. Have your A&P show you how to safety wire the fitting.

Finally, if the aircraft is new to you, consider cleaning out the ball valve. It's not difficult, and can save you headaches with inverted flight. Get the Christen parts manual and look up the O ring spec. Order 2 of them, one for each end. Disassemble by removing the c clips on each end. Wash with mineral spirits and reassemble with new o rings. It's a very simple task, just make sure you put the ball and spring back in the same order they came out.
 
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