Blow by and compression

[Bruce Fenstermacher]

Now that I have the oil leaking out of my pushrod tubes under control about the only major oil loss is from what I think is blow by. When I stop flying and shut down the engine in no time flat there is a puddle of oil from the overflow tube. Looks like about 1/2 oz from an unscientific spill test I just did. And it looks like I'm still loosing about a quart every 4 hours or so. Of course this is an improvement from a quart every 2.5 hours.

Anyway we just did a compression check and all cylinders where 78/80 except for one at 75/80 which was leaking out the valve. These compressions where take cold.

So my question is with compressions that good could I really have excessive blow by pushing oil out the breather?

The front seal doesn't leak and I don't think air is getting past and into the engine case. This engine is still weeping oil from nearly every seam which could also indicate high internal pressure. The engine was clean and dry about 5 hours ago and now better that half of it has the wet look from the weeping. This engine has done this since rebuild about 300 hours ago.

[GAHorn]

With your ear over the oil-filler tube with the cap-removed, blow a little (5 psi or less) compressed air into the overboard tube to be certain it is completely clear. If it is...there is no crankcase pressure problem to worry about.

You can also tape a baggie over the end of the tube and go make a flight. (Do not tape the baggie so as to completely block the anti-icing-cut/hole which is about 10" up from the lower end of the tube, in order to avoid inadvertently pressurizing the crankcase. See how much oil is in the baggie after flight. Chances are, very little.

At what oil-level do you try to keep the sump? (I used to consume 1 qt every 4-5 hours when I tried to keep it up at 7-qts on the dipstick. When I keep it at 6-qts I only use 1-qt every 12-13 hrs.

Which reminds us.... Which dipstick PN do you have installed?

[Bruce Fenstermacher]

I understand that hearing the air entering the overboard tube indicates the tube is open but what does than have to do with to much blow by is blowing oil out the tube?

I should tape a baggy over the tube and fly and see what's in it when I'm finished.

I have the correct dip stick. When I put in 6 quarts which is where I run the oil level, there is 6 quarts on the dip stick. This Sunday I started at 6 quarts. Flew 2 one hour flights. Level is at 5.5 or about a half quart lower. The oil is not in the cowl, it is still dry. It's got to be going out the tube. Couldn't be burning that much oil.

[LBPilot82]

Bruce, you and I seem to be having a similar problem. After about an hour flight I get a good 6 to 10 drops of oil from the breather after shut down (maybe not quite as much as you). If you're concerned it is from excessive blow by at the cylinders, best way to tell should be how quickly your oil is getting dark. I thought I had a problem with blow by but my oil is still exceptionally clean after 20 hours. I've got some oil leaking from the cylinder studs that I have tried to fix without any luck and thought this may have been from excessive crank case pressure. We put an airspeed indicator on the oil filler and ran the engine but never saw over about 20 mph (40-45 should be max). I don't know for sure but I think these engines just tend to breath a lot of oil. I would make sure your breather tube runs uphill before going aft and dropping down and out the cowl to aid in keeping oil in the case. Of course, having said all of that, 4 hours for a quart is still a lot. Are you getting oil down the belly aft of the breather after a flight?? If not, maybe your leaking more than you think and 5 hours since you cleaned it isn't enough time to show it inside the cowling. Just my two cents.

Richard

[Bruce Fenstermacher]

Richard the oil gets dark pretty quick. Haven't actually looked at the belly. Just assumed the oil was there. Actually 1 quart every 4 hours is almost twice as good as it was. The pushrod tubes were leaking so bad it would coat the inside of the cowl in about at hour. So it's been quite a change to have a dry cowl after 5 hours or so.

Were did you get the information about what pressure or in this case airspeed is acceptable? I've heard about doing the airspeed hook up but haven''t ever gotten around to it.

Just would seem a shame to pull these cylinders making the compression they are.

[LBPilot82]

Bruce, unfortunately, I haven't got a very reliable source for the 40-45 mph. I think I saw it searching our forums once, but I came across it on a few websites by searching the internet. So, several sources, none of them TCM. While I'm no A&P (take my advice for what it's worth), it sounds to me like you don't have properly seated rings. If your not leaking all that oil out (and you would definately notice THAT much oil), the only other options are out the breather or out the exhaust. Out the breather at that amount would surely show on the belly while out the exhaust may not. Oil getting dark within a few hours almost surely means too much blow by. ECI says that rings can take upwards of 80 to 100 hours to seat fully but I think if done properly, 25 to more like 50 hours and you should be safe. With 300 hours, yours are either seated or not by now. If you've got access to a borescope or maybe just a flashlight through a plug hole, I would check your cylinder walls. Nice and shiny probably means they are glazed and not seated, but it may be hard to tell. What kind of cylinders did you put on?? (Steel, chrome...) I do know that chrome can be a pain to seat properly. Good news is, if you come to determine that it is unseated rings, it won't be terribly expensive to put on new rings and have the cylinders honed. It will surely be more time and work than you wanted but if you can seal that baby up, it'll all be worth it.

[170C]

Bruce, I think all of our Continentals are going to have some breather tube drainage whether a low time engine like yours or a higher time one. I keep a drip pan under my engine in the hangar and I clean it out every so often so I can see how much is accumulating from the breather and other sources. Its always there on mine with approx 700 hrs since overhaul. I like the suggestion George made with the baggie. I too am going to give that a try and see just how much oil is spilling out of that breather vs from leaks. What is weird is all the flying I did last summer to Missouri, Minnesota, Nebraska & back home (I have forgotten how many hours) I only burned about 1-1/2 to 2 qts of oil & some of that was because I started out with 8 qts and knew I shouldn't have done so. I normally put in 7 qts knowing most of one will go into the filter. Now after reading George's 6 qt recommendation, I may be putting in too much. (George do you have a filter---I don't remember?) My friend has a TIO-520 on his C-206 & it too drips a bit from the breather after each flight so I guess that is just to be expected. I was surprised to learn years ago what Continental says is an acceptable oil consumption rate. Maybe George or someone else will recall what it is and post it here. One question I have about your cylinders Bruce is how did you break them in? Hopefully you didn't "baby" the engine on those first several hours. I have seen several who did and sure enough they ended up glazing the cylinders. Good luck with your investigation. Let us know how much oil you find in that baggie.

[GAHorn]

I understand that hearing the air entering the overboard tube indicates the tube is open but what does than have to do with to much blow by is blowing oil out the tube?...

I'm not suggesting the listening-test would contradict oil is blowing out the tube. You had previously stated:

This engine is still weeping oil from nearly every seam which could also indicate high internal pressure..

Listening for air would indicate you are not building up internal pressure.

It's got to be going out the tube. Couldn't be burning that much oil.

You actually COULD be burning that much oil. Continental actually allows 1-quart per hour as a norm, believe it or not. (See the Form X30013, pg 35) They consider up to .95 lbs of oil per 1/2 hour acceptable. Since oil weighs 8 lbs/gallon (4-qts) that would mean they allow 1.85 lbs per hour, which is virtually a full quart.

Not suggesting WE should accept that level of consumption...only that the mfr considers that amount of consumption to be credible in an otherwise healthy engine.

[blueldr]

If the oil consumption has been high since the time of the overhaul, I'd be willing to bet on failed ring seating.

[n2582d]

Bruce, unfortunately, I haven't got a very reliable source for the 40-45 mph. I think I saw it searching our forums once, but I came across it on a few websites by searching the internet. So, several sources, none of them TCM.

TCM bulletin M89-9 gives 44 mph as a max. reading with the aircraft on the ground. They suggest "excessive crankcase pressure in flight can be induced by ram air entering through an improper fitting oil cap seal and/or defective crankshaft nose seal."

Continental actually allows 1-quart per hour as a norm, believe it or not. (See the Form X30013, pg 35) They consider up to .95 lbs of oil per 1/2 hour acceptable. Since oil weighs 8 lbs/gallon (4-qts) that would mean they allow 1.85 lbs per hour, which is virtually a full quart.

Not suggesting WE should accept that level of consumption...only that the mfr considers that amount of consumption to be credible in an otherwise healthy engine.

TCM contradict themselves in SB03-3 where they say abnormal oil consumption is "an oil consumption rate that exceeds 1/2 quart (liter) per hour during normal engine operation."

As you've had this problem since overhaul I'd suspect that the cylinder walls are glazed. It's a good excuse to buy a borescope. You wouldn't want to go to all the trouble of pulling the cylinders only to find that glazed cylinders were not the problem.

While I don't think this would be getting to the root of your problem it might help slow down the oil loss.

Breather extension.jpg

It has been discussed here back in 2004. If you are interested in pursuing extending the breather elbow I can take some measurements and/or pictures for you of the inside of a O-300 case to verify clearance. But like George pointed out in the referenced post, you'd have to come up with some way of getting the modification approved.

[Bruce Fenstermacher]

BL and Gary I'd agree with you about the glazing or failed ring seating but how do you explain the good compression?

I have two borescopes at my disposal, I'll be sure to inspect the cylinders before I bother to pull them. I did the cylinder work myself and though the fellow signing of the work thinks the honing was fine I've always suspected it. We used a bar hone, all we had available at the time. I've since purchased a ball hone which I used on my C-85. The C-85 has normal oil consumption and no leaks. I've run all my engines hard for break in and really don't baby them under normal conditions. Till recently to save gas I've run them routinely about 100 under red line.

I'm also aware of the extended breather as I've made at least one for installation on another persons engine. This breather never got installed so maybe I'll have to get it back and test it in my engine. I just realized I recently aquired an airspeed indicator and I have a couple of extra oil caps so I'm going to make up a pressure tester and see what case pressure I have.

Sure was a lot easier letting the oil leak and carrying a case of oil with me on longer trips. And being as there is 2 cases of oil waiting for me at W's strip in MN I'd be OK anytime I went that way.

[lowNslow]

Bruce, n2582d (Gary) posted a link to a site a while ago that showed a modified AN840-10 breather fitting with an extended tube. This is used in the C150 aerobat and is supposed to cut down on the amount of oil exiting the breather tube. These are available for the reasonable price of $350 from Hill.
It is just a short length of steel tubing brazed to the AN840-10 ($16). The web site is http://150cessna.tripod.com/c150o200ainsp.html and you have to scroll down a bit to see the pictures. I have not heard of anyone using this on an O-300, so don't know if it would help and of course you have to have a bases of approval.

[GAHorn]

It should be noted that the routing of the crankcase-breather lines are different for the O-200 vs the O-300 engines. The O-200 (to which the extended elbow applies) exits the crankcase and immediately turns downward, which encourages any oil within the tube to exit the engine.

MVC-024S.JPG

The O-300 on the other hand, turns aft and first runs horizontally... and the tube has a slight rise in it (notice where item 55 is pointed) on it's way to the rear cooling baffle, before it turns downward. This different routing encourages oil to remain in the engine. So it's doubtful the extended elbow would be necessary in a C145/O300 and may explain why TCM does not provide for installation in that engine.

crankcase breather.JPG

[davevramp]

Compression or better know as a leak down test is a tool to find problems.
An 80/80 does not mean that everything is fine. I have seen 80/80 and the top ring below the ring land, stuck. I have seen 78/80 and the top ring in 13 pieces. It does check the valve leakage well. Doing a leak down cold with cold fresh oil could be misleading. Even a short run up, hot piston cold hole, will miss lead you. You say that the oil is going black in a short time. Clear indication that the products of combustion are getting past the rings and if so oil will be sucked up in the combustion chamber. High oil consumption will be observed. Car gas should be avoided with high oil usage. There are old procedures that are used on assembly that prolong the break in process. If you would like to talk, PM with phone number and a time to call. I have been here and done a lot of things to get out of this train of events.
Dave

[blueldr]

If it was my engine, I'd be terribly concerned about the proper basis of approval in the use of a modified breather elbow to try to reduce overboard oil loss.