Oil in Air Intake - Please Help

Gman · Post by **Gman** » Sat Oct 06, 2007 4:41 am

Gentlemen,

My O-300-C is leaking oil through the carburetor into the air intake.
Less if the engine has run for less than 30 min, more if it ran for 1h plus.
My MX shop pulled the oil pan, cleaned, heated and dye checked the pan and found a very small crack in front of the carburetor attachment.
We think chances are small that this might be the reason. Pulled the # 4 cylinder, which was the the only one which showed some wet spark plugs.
Valve guide tolerance was deemed as to large and was fixed.
Problem seems less now but is still there.
How in the world can oil get into the inside of the air intake after shutdown?
Any help is greatly appreciated. Should I replace the oil pan and if yes, where could I find one?
Engine has 150 h SMOH in 2000 and runs great, if it wasn't for theat drip on the nose wheel after shutdown. Oil consumption is very, very small (less than half quart in 13 hours).
Is this a flight safety issue, meaning could I just accept it and carry on?

Help, please.

53B · Post by **53B** » Sat Oct 06, 2007 9:14 am

Gman,

We had this same problem with an Ercoupe earlier this year. The intake valves and guides were excessively worn. I would recommend that you pull the intake elbows off and see which ones have oil in them. You could probably tell by taking the intake manifolds off as well.

Hope this helps!

davevramp · Post by **davevramp** » Sat Oct 06, 2007 11:25 am

The intake above the carburetor runs through the sump into a tee that branches out to feed the left and right bank of cylinders. Some of the sumps have a flow diverter that is held in place with 2 rivets. The rivets could be loose and they connect the oil side to the intake.
Please let us know what you find
Miles has a good pic of the diverter. http://www.cessna170.org/phpBB2/viewtopic.php?t=4985
dave

Gman · Post by **Gman** » Sat Oct 06, 2007 3:00 pm

Thanks for the link with the picture. Unfortunately mine has the the flow splitter cast integrally with the sump. I will take some pictures of it and post them.

Gman · Post by **Gman** » Sat Oct 06, 2007 3:06 pm

53B wrote:Gman,

We had this same problem with an Ercoupe earlier this year. The intake valves and guides were excessively worn. I would recommend that you pull the intake elbows off and see which ones have oil in them. You could probably tell by taking the intake manifolds off as well.

Hope this helps!

Thanks for your reply. Both sides have oil in them.
It is basically a new engine with only 150 hours, run fine and compression is 77/80 on all six. I do'n't think there could be excessive wear, but...

I stumbled on this yesterday - could that be the reason:
(quote from an unknow source, please forgive me to copy it)
Question:
"I pulled a cylinder off to fix an oil leak and I forgot to label the pushrods so I couldn't tell which one was for the intake valve and which one was for the exhaust. When I stood them up one was clearly longer than the other by maybe 15 thousands. I thought they were all the same and interchangeable. Does it matter which one goes where/ My mechanic said he thought it didn't matter since they are hydraulic lifters."
Answer:
"The pushrods are the same, BUT, there are two lengths of pushrods listed in the parts manual, standard and P.030. (plus thirty thousandths) When setting up the engine at overhaul and with the lifters bled down, (no oil), the rocker clearance should be .030 to .110. If the clearance is over .110, say .125, a longer pushrod must be installed. The rocker arms are not adjustable, so the only way to change the clearance is to grind the valve face, or grind the valve seat, or to install a longer pushrod to decrease the clearance. Or grind the valve stem or rocker arm to increase the clearance. I also have seen P.070 pushrods listed but I don't know if they are genuine TCM parts. Once the engine is run, the lifters pump up and are filled with oil; the clearance can no longer be checked. The only way to check the clearance is to remove the cylinder and pull the guts out of each lifter and wash all the oil out and reassemble without oil. BTW - pulling the pushrods out can be hazardous on an early engine - the lifters have no circlips and the pushrod cup can come out part way with the pushrod, then get cocked in there and break the lifter when the engine is rotated. If the cylinder is removed it's no problem because the parts can be easily reassembled while the cylinder is off. Did you grind the valves or valve seats? If so, you probably can reinstall standard pushrods. It sounds like you have one P.030 pushrod. If the clearance is below .030 the valve will remain open and will leak. If the clearance is over .110 the engine will clatter from the excess valve clearance. I would install two standard pushrods. If, after an hour or so of running, there is any rocker clearance, install the P.030 pushrod. There should be "0" clearance after the engine is run and the lifters pump up. Standard pushrods are easily obtained from any engine overhauler. I have hundreds of them in my shop, left over from overhauls where P.030 pushrods were installed. It's the P.030 pushrods that are valuable."

Maybe the overhaul shop installed the wrong pushrods causing my engine to 'make'oil?

Post by **Bruce Fenstermacher** » Sat Oct 06, 2007 3:44 pm

No a push rod that is to long will not allow the valve to close and you will have bad compression in that cylinder. I'd return the rod to the valve it came from and assume the overhauler knows what he's doing. Hope you know which side it was or you have a 50/50 shot.

Of course you have already pulled a cylinder and found a guide tolerance that "was deemed as to large and was fixed". Maybe the overhauler didn't know what they were doing?

To be honest I'd be very very leery of your sump with the crack you've found. If you have determined it is a crack I really can't see how you or your mechanic could put it on the engine. It would be unairworthy in my opinion.

Gman · Post by **Gman** » Sat Oct 06, 2007 5:55 pm

The sump is still off and we are looking into finding a replacement (any good sources?) or a way to fix the crack before it goes back on the engine.

Of course, the crack still does not explain how oil can get into the intake.
Any ideas?

Thanks for your reply.

alaskan99669 · Post by **alaskan99669** » Sat Oct 06, 2007 6:01 pm

How far are you taxiing after landing? These engines are notorious for oil bypassing the rings at idling RPM's.

Gman · Post by **Gman** » Sat Oct 06, 2007 7:23 pm

Can't really tell if there is a connection between short and long taxi times (usually long), but it seems that on short engine runs such as 10 minutes there is less of a drip than after one full flight hour.

Thanks for your comment.

cessna170bdriver · Post by **cessna170bdriver** » Sat Oct 06, 2007 8:30 pm

Okanagan Aero Engines in Kelowna, British Columbia has an approved sump repair where they coat the inside of the sump with an epoxy. There's a forum discussion at http://www.cessna170.org/phpBB2/viewtopic.php?t=3746 .

The pushrods come in several oversize lengths to account for wear in the valve train. The overhaul manual gives tolerances for valve lash with lifters deflated. If they don't meet these tolerances, then a different length pushrod is called for. I'd mark them and put them back exactly where they came from.

Miles

Gman · Post by **Gman** » Sun Oct 07, 2007 12:27 am

Thanks for the link. I will call them all and see.

So far I found a 'new' oil sump for $1100.

Any idea on what those repairs would cost and does anybody have any long term experience with the epoxy repair?

Thanks.

Post by **GAHorn** » Sun Oct 07, 2007 3:23 am

The reason oil ends up in the intakes is due to excessive valve-gude clearances. This can be due to either wear or improper reaming during rebuild.

Here's the scenario: The engine is run and oil is pumped by the oil pump to the rocker box cover. The engine is shut down and interior cylinder pressures cease. Oil now runs past the valve guide (no longer having to fight cylinder pressures and/or get sucked into the cylinder due to intake manifold vacuum) and runs down the cylinder intakes to the manifold (down at the carb) and into the airbox.

Similar leakage of oil can occur in the exhaust system, but goes largely unnoticed because hot exhaust gases burn off the oil in the next engine-run. The interior of the mufflers will exhibit carbon from this experience.)

My diagnosis: You have excessive valve guide clearances. (If you also have a cracked sump, that is a different problem.)

Gman · Post by **Gman** » Mon Oct 08, 2007 3:36 am

Thanks for the answer.
That would check because after we pulled one cylinder and fixed the excessive play of the valve guide, the problem (meaning the amount of oil after the next run) was much smaller.
I guess I will have to pull the other 5 cylinders.
What is surprising though is that oil comsumtion has been very low, but I guess this flowback will only occur after shutdown, not while running?
Thanks.

Post by **GAHorn** » Mon Oct 08, 2007 4:51 am

Correct. This type behavior also occurs in fuel injected engines. The intake manifolds have check-valve-drains (intended to drain flooded intakes) which drop the oil onto the ramp a few minutes after shutdown.
I had a Baron that did this for years, and I just allowed it to continue rather than spend the effort and money. It never caused any problem other than a few spots on the ramp.

Gman · Post by **Gman** » Wed Oct 10, 2007 3:38 pm

Alright,
the oil sump is on it's way to Canada for the epoxy treatment.
Will report on progress.
Thanks for all the help.

The International Cessna^® 170 Association

Oil in Air Intake - Please Help

Oil in Air Intake - Please Help

flow diverter

Splitter