Blow by and dark oil Aztec

[Chriscat]

I have a 1973 Aztec non turbo. (540)The problem I am having is in the left engine, the oil turns very dark after about 10 hrs. It also blows the oil out over 8 quarts. It was a factory rebuild and has about 1000 hrs. The lowest compression is 74/80. I have had it to two different mechanics and have two different stories. One is that I have a broken OIL ring. That makes no sense to me because I do not have fouled plugs. The other mechanis says I have a bad front crank seal causing air to pass and build up pressure. That also makes no sense. The right engine has the same time , similar compression, stays around the 9 quart mark and the oil looks like new. Can someone give me some other places to look? Thanks

 

[Mooneymike]

In most cases this is caused by compression gases getting past the compression rings. The oil turns dark because of compression byproducts and the heated gases. If you had a bad front seal I would think you would only have the oil blowing out. A broken oil ring usually results in oil burning in the compression chamber, fouled plugs, and sooty exaust.

 

[bbchien]

So you have blowby, and the products of combustion end up in your case oil (black oil)....AND there's enough pressure in the case from this to blow anything more than 8 qts out the breather tube.

But, it makes power nicely and runs smoothly.

I'm not sure I'd do anything other than look at the cut filter and start sending serial oil analyses. 25 hours later, a ring may have shifted and the problem stops.

 

[Chriscat]

Thank you Bruce and Mike. Is there anything other than bad compression rings that can darken the oil.

 

[Dan Thomas]

I have a 1973 Aztec non turbo. (540)The problem I am having is in the left engine, the oil turns very dark after about 10 hrs. It also blows the oil out over 8 quarts. It was a factory rebuild and has about 1000 hrs. The lowest compression is 74/80. I have had it to two different mechanics and have two different stories. One is that I have a broken OIL ring. That makes no sense to me because I do not have fouled plugs. The other mechanis says I have a bad front crank seal causing air to pass and build up pressure. That also makes no sense. The right engine has the same time , similar compression, stays around the 9 quart mark and the oil looks like new. Can someone give me some other places to look? Thanks

Try checking compression with the pistons at places other than TDC. You'll need a couple of strong guys to hold the prop, and a lower pressure can be used, say 40 or 50 PSI instead of 80. Don't need 80 to find a leak. An engine that runs too cool can suffer corrosion on the lower cylinder walls and leak a lot past the rings in that area.

Lycoming also has had trouble with aluminum piston pin plugs wearing prematurely, letting the pin ends chomp grooves into the cylinder wall. That's below the top of the ring travel, and letting the piston down with pressure in the cylinder is one way to find it. Any lower cylinder wall corrosion can also contribute to pin plug wear, since the rings start cutting into the wall and leave a ridge at the bottom of their travel that shaves the pin plugs. Aluminum in the filter is a symptom. We have a Lyc O-235 in a Citabria that does this halfway to TBO on every engine.

How old, in years, has it been since rebuild?

Lycoming piston pin plugs:

http://www.lycoming.com/support/publications/service-instructions/pdfs/SI1267D.pdf

http://www.lycoming.com/support/publications/service-instructions/pdfs/SI1492C.pdf
http://www.lycoming.com/support/publications/service-instructions/pdfs/SI1492D.PDF

Dan

 

[bbchien]

I was going to suggest as did Dan- but then I recalled that only Continentals have specs for compressions other than at TDC.

I suppose if you were to find hissing amd mid stroke on one cyl, you have to pull it. But I think a borescope woud be the more common response to that condition.

I think I'd still just monitor the engine, oil analysis and cutting up the filters.

Mind you I am not a mech, just someone that has operated C-85s, IO 470s, TSIO 360s, Lyc IO 360s for a couple of thousand hours.

 

[Chriscat]

Both the engines were put on in 2001.
When I talk to the A&P's they always correct me and have their own idea of what to do.I told them that the oil is coming out the breather, they said no. I asked the one that if the oil ring was broken would I not burn oil or foul plugs, he wants to pull the cylinders. My plane is based at an airport with no maintenance facilty. I have to fly and have someone pick me up . Usally the mechanic says it fixed and when I get home there is a puddle of oil under the engine. I'm the one that noticed the oil looked burnt in the engine. Neither mechanic has metioned it. This is after changing just about every gasket on the engine and 3 weeks waiting. Not complaining but that is why I am asking here. I don't know what to do nor do I want them working on the plane anymore. I thank all for responses.

 

[kmead]

We have a constant battle with broken oil control rings, Excessive blow-by, dark oil, and higher oil consumption. Compression check will be great because the 2 compression rings are in good condition. You can find pieces or the ring in the oil suction screen too. With the Mirage I look for which plug and cylinder has the most oil, sometimes only one cylinder is causing the problem. Pulling one cylinder would be much better than pulling them all.

Kevin

 

[Ted]

One thing you don't have to worry about on an Aztec is the engine running too cool.

My general suggestion is to do nothing. If compressions are good and the engine appears to be making power, then it's probably not an issue. Just keep an eye on the filters, as has been stated, and if it's making metal then you want to investigate the cause. The right engine on my Aztec at 1500 hours SMOH and it has similar behavior (at least as far as the dark oil is concerned).

 

[Chriscat]

Today I took a hose from the breather and hooked it up to the airspeed indicator. Much to my surprize both engines were the same. At 1000 rpm 50mph at 1500 it was 75mph and at 2000 it was 95mph. I am told that lycoming has a bulletin that tells you what these readings should be. Does anyone know what these should be?
Thanks for all your answers.

 

[N801BH]

Today I took a hose from the breather and hooked it up to the airspeed indicator. Much to my surprize both engines were the same. At 1000 rpm 50mph at 1500 it was 75mph and at 2000 it was 95mph. I am told that lycoming has a bulletin that tells you what these readings should be. Does anyone know what these should be?
Thanks for all your answers.

Aw come on,,,, say you used an old airspeed indicator that you had laying around and not the one mounted in the panel of your plane ...

 

[Let'sgoflying!]

At 1000 rpm 50mph at 1500 it was 75mph and at 2000 it was 95mph. I am told that lycoming has a bulletin that tells you what these readings should be. Does anyone know what these should be?

This says 90mph in flight(!):
http://www.121five.com/admin/FeatureArticles/Superior_Excessive_Oil.pdf

This says 45-50 up to 100mph idle to full power:
http://www.sacskyranch.com/eng30.htm

some Lycoming SBs
http://www.lycoming.textron.com/support/publications/service-bulletins/index.html

You probably saw their troubleshooting guide, no 'dark oil' but might give you some ideas:
http://www.lycoming.textron.com/support/troubleshooting/resources/Trouble-Shooting-Guide.pdf

 

[TangoWhiskey]

OK, this "piston pin plug"... what is it? I'm not a gear head, have never built an engine, but I understand how they work. A diagram would be great.

Does it connect the connecting rod to the piston?

 

[Let'sgoflying!]

It is a cap on each end of the piston pin, and slides along the cylinder wall with the piston as it moves up an down. The pp joins the conn rod to the piston. It slides into a hole on each side of the piston and a similar hole in the conn rod.
Incoming diagram/photo.

 

[TangoWhiskey]

Thanks Dave! Go figure, the descriptive name was actually accurate. Are they recessed slightly? The outside of the piston has a curve, and my gut is saying that a non-curved piston plug that "slides along the cylinder wall with the piston" would score the wall.

The piston is that hollow inside? I knew it was machined on the crankshaft side, but didn't realize it was to that degree!

 

[Let'sgoflying!]

Yeah, pretty lightweight. I think most of the hollowness is from forging or casting rather than cnc.

 

[murphey]

Chriscat:
If we knew what part of the country you're located, we could provide some recommendations for other shops.

 

[Tom-D]

Mind telling us what cylinders and what ring set was installed at the overhaul, and how/who did the run in?

 

[Chriscat]

It was a factory rebuild. I am not sure what was used in the rebuild. I was told that they were chrome. I don't know who broke the engine in. The plane is based in WV at PKB. Two mechanics have done compression checks with the lowest being 78/80. One of them is telling me that the front crank seal is allowing air into the crank case when I fly and causing high pressure in the case.

 

[Dr. O]

Ahhh jeez... Take it to a mechanic with a borescope... Normally, a piston top with excessive blowby will be darker around the periphery due to the hot gas flowing past...
If there is a problem with the wrist pin caps to the point that the cylinder has blowby, there will usually be a scoring on the cylinder wall..
A stuck ring can give you a good leak down reading but will shudder and have blowby when the engine is making significant power...
A cracked piston land can have a good leak down yet blowby under high power...

Personally, I cannot stand an engine that is questionable... You can bet if it is piston/ring/pin problem it is gonna bite you with a bang, right on takeoff on a dark and stormy night... Borescope it... If nothing is found, pull the cylinders for a hone and ring job...

denny-o

 

[Tom-D]

It was a factory rebuild. I am not sure what was used in the rebuild. I was told that they were chrome. I don't know who broke the engine in. The plane is based in WV at PKB. Two mechanics have done compression checks with the lowest being 78/80. One of them is telling me that the front crank seal is allowing air into the crank case when I fly and causing high pressure in the case.

Knowing it was a factory overhaul, and the cylinders are chrome, they should be marked with a orange base color, are your cylinders painted orange at the base where they bolt to the crankcase?

IF SO........ you need to have a new set of rings placed on all pistons and run in again. Chrome cylinders are noted for this problem, your rings never seated. they will give very nice compression readings but the cylinder is rough and allowing blow by to carry carbon into the oil sump.

BE positive the mechanic who does this, does not re-hone the chrome cylinder. or you will be buying all new cylinders for that engine.

 

[Henning]

So you have blowby, and the products of combustion end up in your case oil (black oil)....AND there's enough pressure in the case from this to blow anything more than 8 qts out the breather tube.

But, it makes power nicely and runs smoothly.

I'm not sure I'd do anything other than look at the cut filter and start sending serial oil analyses. 25 hours later, a ring may have shifted and the problem stops.

Except that if it is a broken ring, rather than changing out a ring now, you'll change out a whole jug set later. I'd borescope and see if there's any sign of a broken ring and fix it if there is. Rings are cheap, the labor is the same so "pay me now or pay me later" on that and save the price of a jug. If the jug has already been ruined, well, might as well change it before it goes full bad and costs a few extra thousand plus whatever the delay/lost trip/hassles of having to do it away from base are.

Do the compression test again listening to the breather tube, if it's a broke ring, you'll hear the difference when you get to the bad cyl. Borescope that cylinder (might as well have a peek at all of them anyway) and see what you can see. If I heard a difference but didn't see anything, I'd still be inclined to pull that jug. It's really not that big of a deal to pull one jug off most engines/applications.

 

[Henning]

It was a factory rebuild. I am not sure what was used in the rebuild. I was told that they were chrome. I don't know who broke the engine in. The plane is based in WV at PKB. Two mechanics have done compression checks with the lowest being 78/80. One of them is telling me that the front crank seal is allowing air into the crank case when I fly and causing high pressure in the case.

Ahhhhh, orange cyl bases or fins? If so....common problem, you need to just pull the jugs and put on new rings if there is no damage. Chromes are sometimes a ***** kitty to seat up. You'll see fine compressions on a compression test, but that's really only a half hearted test when given what combustion pressures are.

 

[Chriscat]

I had a compression test done while I watched. He did it at top DC and bottom . The compression was all 78 or better. He couldn't believe the compression was that good. He also borascoped each cylinder and could not find and problems. He cut the oil filter and found no metal. He told me to carry some shop towles or install oil seperators.
Thanks for all the replys.

 

[Tom-D]

I had a compression test done while I watched. He did it at top DC and bottom . The compression was all 78 or better. He couldn't believe the compression was that good. He also borascoped each cylinder and could not find and problems. He cut the oil filter and found no metal. He told me to carry some shop towles or install oil seperators.
Thanks for all the replys.

The problem you have is a stupid A&P..........

Are your cylinders Chrome, ??? do they have orange markings ???

 

[RotorAndWing]

I had a compression test done while I watched. He did it at top DC and bottom . The compression was all 78 or better. He couldn't believe the compression was that good. He also borascoped each cylinder and could not find and problems. He cut the oil filter and found no metal. He told me to carry some shop towles or install oil seperators.
Thanks for all the replys.

The reason you have such good compression readings is all the oil in the cylinders making a good seal.

Find another mechanic.

 

[FORANE]

Resurrecting an old thread...

My O-320A has 3 chrome cylinders with 10:1 pistons and about 800 SMOH. I have had the same problem as the OP of losing oil out the breather as long as I have had it (all those hours). Compressions have been 76/80 or better. Using 50w oil I typically have to add 1 quart every 2-3 hours.
I take it by the posts on this old thread that poorly seated rings are the likely cause. Other than adding oil a little more often, is there a downside to just continuing to run it? Is there a method to identify the bad cylinder?

 

[N801BH]

Resurrecting an old thread...

My O-320A has 3 chrome cylinders with 10:1 pistons and about 800 SMOH. I have had the same problem as the OP of losing oil out the breather as long as I have had it (all those hours). Compressions have been 76/80 or better. Using 50w oil I typically have to add 1 quart every 2-3 hours.
I take it by the posts on this old thread that poorly seated rings are the likely cause. Other than adding oil a little more often, is there a downside to just continuing to run it? Is there a method to identify the bad cylinder?

Look at the spark plugs closely... And the exhaust ports too..

 

[FORANE]

Look at the spark plugs closely... And the exhaust ports too..

Just came through annual this month. #1 cylinder lower plug did have a little wet looking oil residue. Most likely culprit I guess but anyway to confirm before pulling?

 

[Tony_Scarpelli]

I have heard nothing but bad news from Chrome Jugs. If I were going to take the time to take this jug off, I would replace it with a rebuilt CirmiNil jug and be done with it.

When and if I had trouble with the other three Chrome jugs I'd do the same. Go to Aviation Consumer Reports-Chrome was a bad idea.

 

[FORANE]

I have heard nothing but bad news from Chrome Jugs. If I were going to take the time to take this jug off, I would replace it with a rebuilt CirmiNil jug and be done with it.

When and if I had trouble with the other three Chrome jugs I'd do the same. Go to Aviation Consumer Reports-Chrome was a bad idea.

Agree 100%. This has been my experience and exactly what I have read about chrome jugs with the only possible exception they might offer a little anti-corrosion benefit for those who do not fly much.

I have heard, read and it has been my experience that new jugs are better than rebuilt. What is a CirmiNil jug and why would I want one over a new jug?

 

[Ted]

I have heard, read and it has been my experience that new jugs are better than rebuilt. What is a CirmiNil jug and why would I want one over a new jug?

New jugs are better than rebuilt, provided you buy factory Lycoming jugs. Honestly, only ones I'd spend the money on for a Lycoming engine. Continental is another story.

The cost/benefit question of new vs. rebuilt is how long you plan on keeping the engine prior to overhauling it. If it's at 800 SMOH now and an O-320, you could look at the TBO as 2,000 hours, or alternately you could expect to get many more hours out of the engine. When I was faced with this decision on the Aztec, I purchased new factory jugs. They were trouble-free, but I also sold the airplane about 600 hours later. Realistically I could've done a cheaper option and probably had similar reliability.

If you've got 3 chrome cylinders and chose to top the engine with new factory Lycoming cylinders, you'd probably be good to well past 2,000 hours, provided you have a solid bottom end that will hold up. And even if that doesn't happen, then you have good cylinders you could use on your rebuild already. I tend to think a good set of factory cylinders is good for two runs pretty trouble-free.

 

[Tony_Scarpelli]

I've had good luck with rebuilt cylinders which have had the nickle treatment made popular by ECI. you cannot buy a new Lycoming jug with CemiNil so it is a trade off between paying more for a new lycoming, which I agree there is nothing wrong with a new lycoming cylinder, or getting a rebuilt cylinder with the CermiNil treatment.

If you fly weekly it won't matter either way. If you fly infrequently the CermiNil offers a bit better protection like the Chrome was supposed to do. Problem is that the Chrome is too hard and chips. CermiNil puts an almost eazy cooking pan finish on the jugs described as an almost spider web like pattern which also helps disperse oil better than the original jugs according to my engine building buddies at RAM, Savvy Aviator IA M. Bush and Aviation Consumer. I am sold on CermiNil since I have discovered them and put them on both my Cherokee 8years ago which lasted 3475 hrs past TBO and my Turbo Comanche 4 years ago. I do not think you will go wrong with new Lycoming either. I just perfer the CermiNil.

 

[Dr. O]

On my Apache O-320 engines I used to have the oil go dark within 20 hours after an oil change, It was not blowing oil out but was consuming it about a qt to 2-3 hours (depends on power setting)
The engines are high time 5000 and 6000 hours total and had 900 and 1600 hours respectively since the bottom ends had been overhauled. And we found a cracked cylinder one day chasing a low leak down test, so the time had come. (They were overhauled cylinders that had been put on at various times. The previous owner was "very" frugal)
I tried to get new Lyc cylinders but couldn't. ECI had them. Discussed with my engine guy and he is comfortable with taking the bottom ends out to near 4000 hours SMOH.
So, we put 8 new Titans on with ECI moly rings and Lycoming wrist pins.
While the cylinders were off we did as good an inspection of the bottom end as we could - borescope, mirrors, etc. Everything was clean and tight, the con rods had no slop and the cam looked great. I also sent the oil coolers out for testing and installed new Vernatherms, some new hoses, etc.
Have a few hundred hours on the new cyllinders now. Biggest problem is the oil stays clean and bright and I have to remember to check the logbook or I go over my 50 hours. Before it always got dirty enough at about 35-40 hours that I was changing oil because it looked and smelled grungy.
So, pull a cylinder and check the cam and inspect the bottom end. If it looks good don't be afraid to put on new cylinders.

 

[N801BH]

On my Apache O-320 engines I used to have the oil go dark within 20 hours after an oil change, It was not blowing oil out but was consuming it about a qt to 2-3 hours (depends on power setting)
The engines are high time 5000 and 6000 hours total and had 900 and 1600 hours respectively since the bottom ends had been overhauled. And we found a cracked cylinder one day chasing a low leak down test, so the time had come. (They were overhauled cylinders that had been put on at various times. The previous owner was "very" frugal)
I tried to get new Lyc cylinders but couldn't. ECI had them. Discussed with my engine guy and he is comfortable with taking the bottom ends out to near 4000 hours SMOH.
So, we put 8 new Titans on with ECI moly rings and Lycoming wrist pins.
While the cylinders were off we did as good an inspection of the bottom end as we could - borescope, mirrors, etc. Everything was clean and tight, the con rods had no slop and the cam looked great. I also sent the oil coolers out for testing and installed new Vernatherms, some new hoses, etc.
Have a few hundred hours on the new cyllinders now. Biggest problem is the oil stays clean and bright and I have to remember to check the logbook or I go over my 50 hours. Before it always got dirty enough at about 35-40 hours that I was changing oil because it looked and smelled grungy.
So, pull a cylinder and check the cam and inspect the bottom end. If it looks good don't be afraid to put on new cylinders.

I agree 100% with the concept...

 

[Tony_Scarpelli]

If your oil is light in color I do not think I would bother changing it on such a short time interval. I did 100 hr changes in the Cherokee, with the Turbo I do 50 hrs.