Aerobatic Breather Mod

[Kerbs]

I wanted to thank Tim (astjp2) for his help modifying the crankcase breather for the C85 to an aerobatic breather. Quality of workmanship is top notch. I was always cleaning the belly with the previous engine and am hoping this will help to cut down on that.

[PA1195]

If that doesn't fix it route the breather line over the front cylinder base and down in front of the rear one. I had to do that on a C-90 even with this extension. And insulate the line if freezing temps are expected.

Gary

[N96337]

I just did a 65 with it, and it did a nice job of cleaning up, but he didn't have a big problem to start with either.
John

[PA1195]

We should ask about the why of excessive blowby. If it's combustion leakage passed piston rings and exhaust valve guides then fix that first. Do cylinder leak down checks and have a look inside the valve covers for exhaust gas cooking oil. Some have tapped an airspeed indicator into the oil filler cap to look for excessive crankcase pressure:

https://www.121five.com/admin/Featur...essive_Oil.pdf Also see TCM SB M89-9 http://www.csobeech.com/files/TCM-SB-M89-9.pdf

It might also help to drill a small lower drain hole in the added vent's extension so oil that passes by has a way back into the crankcase. Or add a whistle slot to the lower breather tube as explained in the link.

Gary

[LostnSpace]

Thank you, I was just talking to an engine builder about the airspeed attach today, Gary

[astjp2]

Thanks for the vote of confidence Stu, I am glad you liked it. I got your letter. I just did it to mine a few month ago, my belly was always covered. I am thinking I might do the "real gaskets push rod tube modification." I should really wash the engine down. I just wont use purple power though, very corrosive to engine. Tim

holy crap what a bunch of incomplete sentences. Gary my compressions were 80/80 cold and hot and I still had oil on the belly. Some engines just do that. Tim

[PA1195]

Manufacturers typically determine sump oil capacity based upon max allowed oil consumption per hour versus expected fuel range. That means the sump is often overfilled for the mission assuming oil consumption is normal. Try dropping the oil level 1/2 quart to the add level and see if blowby and consumption are reduced. Experiment. Common knowledge among we Harley owners and others that have experienced it in aircraft engines.

See page 104 and on for oil capacity vs fuel consumption> https://www.faa.gov/documentLibrary/.../AC_23-16A.pdf

Gary

[astjp2]

Manufacturers typically determine sump oil capacity based upon max allowed oil consumption per hour versus expected fuel range. That means the sump is often overfilled for the mission assuming oil consumption is normal. Try dropping the oil level 1/2 quart to the add level and see if blowby and consumption are reduced. Experiment. Common knowledge among we Harley owners and others that have experienced it in aircraft engines.

See page 104 and on for oil capacity vs fuel consumption> https://www.faa.gov/documentLibrary/.../AC_23-16A.pdf

Gary

Oil capacity is also a function of cooling capacity, more oil=more cooling in an air cooled engine.

[PA1195]

Oil capacity is also a function of cooling capacity, more oil=more cooling in an air cooled engine.

Yes of course and 14 CFR Part 23 notes that: Edit: Should have said "AC 23-16A notes that"

"How much oil must the system contain?

Paragraph 23.1011(c) requires that, “The usable oil tank capacity may not be less than the product of the endurance of the airplane under critical operating conditions and the maximum oil consumption of the engine under the same conditions, plus a suitable margin to ensure adequate circulation and cooling.” In other words, there needs to be enough oil (usable supply) to allow the engine to consume the usable fuel. This should be substantiated by a quantitative analysis.

In addition, a suitable oil quantity margin for system circulation is necessary for all engine installations. The oil system should be capable of maintaining the engine within its operating limitations (i.e., oil temperature with the minimum oil quantity provided for circulation). Cooling tests do not need to be performed with a low usable oil supply provided the oil is properly cooled at all oil levels."

And both CAR4 04.630 and CAR3 3.561/3.581 previously suggest cooling and safe operation are a consideration when determining sump capacity. Some engines like my C-85-12 have an oil cooler pad to help in that process.

Gary

[astjp2]

Yes of course and 14 CFR Part 23 notes that:

"How much oil must the system contain?

Paragraph 23.1011(c) requires that, “The usable oil tank capacity may not be less than the product of the endurance of the airplane under critical operating conditions and the maximum oil consumption of the engine under the same conditions, plus a suitable margin to ensure adequate circulation and cooling.” In other words, there needs to be enough oil (usable supply) to allow the engine to consume the usable fuel. This should be substantiated by a quantitative analysis.

In addition, a suitable oil quantity margin for system circulation is necessary for all engine installations. The oil system should be capable of maintaining the engine within its operating limitations (i.e., oil temperature with the minimum oil quantity provided for circulation). Cooling tests do not need to be performed with a low usable oil supply provided the oil is properly cooled at all oil levels."

And both CAR4 04.630 and CAR3 3.561/3.581 previously suggest cooling and safe operation are a consideration when determining sump capacity. Some engines like my C-85-12 have an oil cooler pad to help in that process.

Gary

Part 23 is an airframe regulation. Engines are certified by part 33, https://www.google.com/url?sa=t&rct=...OoVZ0_lTAy5dQr

[PA1195]

Tim you're a tough one to convince what I posted in #8 was in fact only that. Read the AC 23-16A. It's a non-regulatory consolidation document not limited to 14 CFR 23 or 33. I incorrectly referred to this AC as "14 CFR 23" above. The quote in #9 is from the AC and not 14 CFR part 23. It lacks that weird $ sign in front of the paragraph.

14 CFR 33 is indeed the certification and Airworthiness Standards document. It's a run and teardown test procedure. Prior to that it also notes:

"§ 33.39 Lubrication system.
(a) The lubrication system of the engine must be designed and constructed so that it will function properly in all flight attitudes and atmospheric conditions in which the airplane is expected to operate. In wet sump engines, this requirement must be met when only one-half of the maximum lubricant supply is in the engine.

(b) The lubrication system of the engine must be designed and constructed to allow installing a means of cooling the lubricant.

(c) The crankcase must be vented to the atmosphere to preclude leakage of oil from excessive pressure in the crankcase."

Now the question becomes what CAR or CFR applies to small Continentals A-65 through O-200? CAR part 13 1937-1956 was the document in effect when they were certified and precedes FAR 23. CAR 13.112 is repeated by 33.39 above. Good. But obviously AC 23-16A Paragraph 23.1011(c) I linked above is more detailed. I suggest the AC better describes the CAA and now FAA's intent when it comes to engine oil. And, obviously any reduced oil level must meet $33.39 so cut back on the fill level and see what it does to blowby.

Gary

[PA1195]

The Continental A-65 through O-200 were certified under CAR 13. Here's a copy. Never be concerned about running them hard.

Gary

[Ragwing nut]

Alot of times, placement of the end of the breather will be in a low pressure area and will be sucked out the breather tube. It won't be an engine issue. I have only had to do this mod on one airplane, it was an Ercoupe with a C90 installed.

[PA1195]

Alot of times, placement of the end of the breather will be in a low pressure area and will be sucked out the breather tube. It won't be an engine issue. I have only had to do this mod on one airplane, it was an Ercoupe with a C90 installed.

Yes and this from above (https://www.121five.com/admin/Featur...essive_Oil.pdf) recommends an anti-siphon hole or slot be installed upstream to reduce crankcase oil mist loss. We do that in cold climates to prevent freezing of the oil/water mixture and blocking the breather tube.

I had a C-90 in a PA-11 that liked to blow oil. We installed Tim's internal breather extension, ran the hose up and over to discourage flow, and placed the end of the tube in several locations. First it was on a mid-time engine, then a topped engine, and finally after a major overhaul. Rings and valves were tight on the latter two. Still blew oil until I started running the sump level 1/2-1 quart lower than full (4.5 to 4 total in a ~5 quart sump). Blowby nearly quit and returned after I filled the sump. My fix.

Gary

[N96337]

One thing to watch for is low spots in the breather lines too. The oil can pool up and block just long enough to cause problems. I had a 1340 out one time to a well known Ag operator repair service, and they called and said our engine smoked. I knew it was fine when I bought it off the test cell a week earlier, so I drove over. They'd installed the breather tube facing forward. They still wont own up to that.
John