O320 oil consumption and fouling

[Jab]

Hi all

I have an RV4 with a carbureted Lycoming O320 A3B and I am having fouling issues despite agressive leaning. I started using TCP additive and it seemed to help but yesterday the engine was just generally rough and the lower #3 plug had liquid oil inside the plug when I pulled it. I just replaced the lower plugs with Tempest UREM37BY plugs to see if they help. A factor is that I generally fly below 5000 feet and most often around 1500 feet, any leaning at that altitude results in the occasional missing and rougher running. Flight profile is cross countries of 70 miles or less and aerobatics. It does have an air/oil separator.

The oil consumption is around 1 quart every 4 hours and there is oil coming out of the breather, I am running the level at 5 quarts to make sure excess oil is not being blown out. The 1974 remanufactured engine has around 750 hours so it has been standing for a substantial part of its existence but compressions are 76 to 78 on all cylinders so I don?t think rings are the issue.

I also flew a Beech Musketeer with an O320 and it was smooth as a sewing machine, much smoother than my engine and there was no need to lean it out to avoid fouling. I am going to speak to an engine shop but any suggestions or advice will be appreciated before I do so, I want to do a lot of troubleshooting before I take it in to the shop so I can eliminate the usual causes.

Thanks, Gary

[n82rb]

The bad news is at 4hrs per qt, and oil fouled plugs you have either valve problems or ring problems. With oil in the breather I'm going with rings. A compression check should tell you a lot.

Bob burns
Rv-4
N82rb

[DHeal]

Sorry but the engine is 44 years since reman with an average of 18 hours per year (with long periods of non-use) and is evidencing signs of wear / distress -- it deserves an overhaul. I would certainly question the condition of the cam / lifters.

[Jab]

Thanks for the input gentlemen.

Bob - The compressions are 76 to 78 on each cylinder so rings appear to be ok, could you please explain the valve problems you mentioned, trying to figure out where the oil is coming from.

David - I agree it?s an old engine, that?s why I am trying to see what I need to overhaul first.

[Steve Barnes]

Dave is referring to worn valve guides that allow excess oil through. I believe that your oil consumption is at the lower end of Lyc's acceptable range for oil consumption but still OK.

Steve

[RV6_flyer]

Do you have Chrome cylinders?

[n82rb]

Originally Posted by Jab

Thanks for the input gentlemen.

Bob - The compressions are 76 to 78 on each cylinder so rings appear to be ok, could you please explain the valve problems you mentioned, trying to figure out where the oil is coming from.

David - I agree it?s an old engine, that?s why I am trying to see what I need to overhaul first.

If you have oil fouling of plugs the oil can only be coming from two places, by the rings or through the valve guides. Oil blowing out the breather is usually caused by the crankcase being pressurized by ring blow by. If you have a lot of oil coming by the rings you sometimes get false high readings on a compression test because the oil helps seal the rings to the cyl.
Bob burns
Rv4 n82rb

[lr172]

As mentioned, excess oil in the combustion area only comes from two places. The oil rings, not the compression rings determine how much oil gets left on the cylinder walls. Excessive oil consumption from the rings is typically attributed to the oil rings or imperfections on the cyl wall (improper scraping action leaves too thick of a film on the wall and it burns during the combustion), therefore a successful compression test does not eliminate the rings/cylinder walls as a source of the oil (compression test only confirms proper seating of the compression rings with the cyl wall at the very top of the cyl). Lycomings don't put a lot of oil into the rocker box to begin with and gravity helps to keep it from going down the guides and into the combustion chamber. Therefore, it makes the guides a less likely source for the oil. A quick look into each intake and exhaust port will show you if a guide is the source.

Excessive blowby can increase oil consumption, but it is due to blowing atomized oil out the breather and not burning it. The presence of wet oil on the plugs indicates an oil burning condition. That and the compression readings point to burning, not blowing it out the breather.

You can also borescope a few cylinders. Pitting or scoring on the walls will increase blowby without showing poor compression.

Larry

[smokyray]

Gary,
Great info shared above. When (not if) you decide to remove and overhaul, which as an A&P and many hour Lycoming driver highly advise, there are 2 shops near you I can recommend.
As a former Central Floridian, I know both well.

Zephyr Engines in Zephyr Hills. http://www.zephyrengines.com/
JB Engine Overhaul in Sebring. http://www.jbaircraftengines.com/

Like the Dentist said, "you can pay me now, or pay me later, but either way it's gonna hurt."

V/R
Smokey

[Jab]

Thanks for all the great feedback, I really appreciate the helpfulness of the people on this forum. I did get a borescope into the cylinders today and they look fine, the valves looked good too but there was oil on the #3 lower plug and as Smokey said, you gotta pay sooner or later so I am taking the jugs off in the next day or two. Smokey, thanks for the links to the shops, I will get in touch with them tomorrow. I also heard good things about Jurnigan, I may go see their operation and have a chat.

Have a great evening and thanks again gentlemen.