leaky engine

[ablight]

Group

I have a newly overhauled C85-12F in my champ. Columbia aircraft did the overhual, I am very happy with their service. I also had the O-200 STC done and the carb rebuilt. Ater every flight I have to clean the cowling behind the air filter of a fuel oil mixture. It is leaking from the carb air box and out the bottom of the filter. Before each flight I have to clean the bottom of the air filter box. The engine has 30 hours since rebuild (new millenuims). I have been using 100 or 65 mineral oils. Any advice/ideas is appreciated. Andy

[Mikek]

Group

It is leaking from the carb air box and out the bottom of the filter. Any advice/ideas is appreciated. Andy

Andy,

Might need to take it one step at a time. Oil/fuel can travel great distances
before they find a place to show their face. My A65/A75 and others have
a baffle that scoops the air in from the front to under the engine case
which also acts like a catch pan. Oil from both ends of the push rod tubes
along with fuel from the intake tubes and or a leaking primer line or fitting.
There are several outlets around the Carb intake spider and just above
the air filter bracket.

First:

If you are able to remove the cowling upper and lower and then use air
sprayer and wash down engine, cowling and all chafing cowling seal which
holds oil.

Install cowling start engine run for just a 2-3 min. @ 1000 rpm then shut
down and remove the TOP cowl, now go get a cup of coffee or pop and
just wait. Might need to wait 1-2 hrs, then start by looking at the lower
cowl for signs of oil/fuel, then wipe with your finger the BOTTOM of each
valve cover, then behind cylinder by upper end of push rod tubes. If you
find all dry, then look at lower cowl one more time. If you find nothing
remove lower cowl and check the lower clamps on push rod tubes for oil
hanging wipe your finger under mags, tack, oil temp, and filter.

If still dry check it the next day.

Sorry I have a problem of going on and on but this needs to be done step
by step and fix each one you find a start again at step one clean down
the engine.

Good luck, many have tried and only a few have won!! Hope you are
one of the few!!!

Mike Kne

[Bob Eilers]

I have a C-85, on a 1946 7BCM, I have the same situation - however it is intermitent. I have gone through the engine inspection process and have spoken to members of my EAA group, who also fly older aircraft with the updraft carbureator. I have come to the conclusion the leak is fuel from the carbureator. In many of these older airplanes, during the start process, fuel will drip from the air box. I don't worry about it.

[Mikek]

fuel will drip from the air box. I don't worry about it.

Same here during the priming either by turning the prop or using the
primer pump the graivity will drain fuel down to the airbox from the intake
spider and tubes. Once it starts the suction from the intake keeps it where
it belongs.


Mike Kne

[MikeB]

I agree with Mike K and Bob E. Mike's ideas for looking for oil leaks make good sense, however, I think what you're looking at is fuel dripping out of the updraft carb, either through priming or after you shut the engine down (a little always seems to leak out). My old "white bellyed money sucker" always seems to have a mess on the cowl and under the air cleaner. I've determined over the years that it's pretty much fuel. Not likely that you'd have oil coming out of the air box.

[7DCDRIVER]

I have same problem with my c85-12. Seems to be a mix of gas and oil - mostly gas.

I am also curious as to how long it should take to run out the fuel after you have turned off the fuel valve (YES, ON THE GROUND, BEFORE ONE OF YOU TRIES TO MAKE A COMMENT ON NOT DOING IT IN THE AIR !!!!)

Love to hear of how others have cured the leak problem. problem

[Ron Babos]

The engine could run for about 90 seconds, depending on the rpms. What I do is shut the fuel off coming around the hanger, set it to 1200 and when it starts to quit, open throttle to full. Don't forget to bring it back to idle and turn the mags off. This way there is not a drop of fuel coming back into the carb box. If you are running MMO it will look like oil as it drips back through the box along with the gas. Also check those pesky cylinder base rings for leaking.
Ron

[ablight]

Thanks for the replys. My engine will run for about 45 seconds until it runs out of fuel (with the selctor turned off). Just enough time to taxi back to the hangar.

The fuel however is mixing with oil when it comes out of the carb. I'm not so much concerned with the fuel dripping as I am with the oil coming out the carb air box. Could this oil be leaking past rings that may not have been seated yet (correcltly) and out an open intact valve?? I am burning about a qt. every 4 to 5 hours - 25 to 30 hours since overhaul. WIth every thing new #$@*!!.

The color is grenish blue - yellow (oil) and blue (gas) make green you can tell by the feel of it as well. Sooo should I be worried or just fly it. Thanks Andy.

[Mikek]

The fuel however is mixing with oil when it comes out of the carb. I'm not so much concerned with the fuel dripping as I am with the oil coming out the carb air box. Could this oil be leaking past rings that may not have been seated yet (correcltly) and out an open intact valve?? I am burning about a qt. every 4 to 5 hours - 25 to 30 hours since overhaul. WIth every thing new #$@*!!.

Thanks Andy.

Newly overhauled 1 qt. 4-5 hrs not bad at all. Might clean up the airbox and carb air intake area, then fly it, check carb air intake area see if it
is fuel or fuel & oil mix.

Also, check compresson and plugs, not an A&P but if you are getting oil in
the fuel chamber should show up on plugs and during comp. check.

Nothing that I would worry about engine still breaking in.

Mike

[LOWELL]

What type of air filter do you have. Have you checked the IN. guide
to valve clearance. Have you pulled any IN. tubes to check for oil. If you
are getting oil thru the carb on shutdown it has to come from the Cylinders
or you might have one of the old type air filters that requires cleaning and
oiling. It might be draining back to the rear of the box.

[Ron Babos]

Oil will sometimes go through the intake valve guides and collect in the elbow and runners. It's only normally a mist coat, but add some fuel to it and it will make a mess. As the engine is not seated yet, and blow-by is higher than normal this will force more oil through the intake guides than normal. Go fly the sucker, and don't baby it until oil consumption drops. This could take up to 100 hours depending on how much out of round the cylinders have become from heat cycles on your engine. It's only a few 1/10 s of a thousands but it will cause blow-by and oil burn. Just re-did my 65 that had 30 hours on it due to a case problem. It had lots of blow-by prior to tear-down and had not seated . During the case re-fit I ran a hone through each of the Milleniums, and could see the out of round condition. They were reinstalled into their original # postitions and low and behold, never had oil consumption or blow-by since start-up. This could explain why some engines break-in in about 5 hours, and some take forever, as the cylinder needs to be worn round again or the ring worn to fit it for sealing to occur. High load, full throttle is the best and only way it will happen.
Ron

[MikeB]

Ron,
Are you saying ( I guess you are) that the cylinders were out of round from the factory? Considering "aircraft quality and inspection" that hardly seems possible.......not! I agree though, that it looks like Andy should just go and fly the thing hard until the rings seat. It's certainly possible that one or more cylinders could be pumping a small amount of oil and letting it run out a open intake valve when the engine is shut down. I guess I've never paid much attention to the problem as you see a lot of Champs with dirty "beards" below the air cleaner. Mine certainly does.....read my next post.

[Ron Babos]

Mike: No I'm not saying that. From the hone they are or should be round. Installing them on a crankcase flange that is less than perfect will warp the new cylinder some. Again I'm not talking 1/4 inch here but a meer .0002 or so out of round. What really warps them is the uneven cooling that occurs from normal operation. The heat cycles will cause a mini form of hoop stress to the cylinder or the heat acts like a stress relief to the steel cylinder. After a few exposures to all this, they retain this shape and stay there, pretty much. As for the aircraft quality and inspection you mention, I have one channel chrome cylinder in my basement that is ground below the minimum dia. Another has the choke at the base instead of the head. Bottom line is check everything first before using it. Nothing worse than having to do it twice. Been there , done that, finally clued in.
Ron

[ablight]

Thanks for all the replys. Good advice. I have noticed that with 100 weight oil the blow buy is less than with 65 weight. Andy