Glazed Cylinders Question

[ShyFlyGuy]

Recently, I had a top overhaul done to my 152. I have reason to believe that the mechanic who did the run-up for the leak check, and the final run-up might have glazed the cylinders. I've put more than 50 hours on it and continue to fly it. We're going to resolve the issue in a few weeks, but is there any danger to continuing to fly the aircraft between now and then?

Your input is always appreciated,

Shy

 

[avbug]

glazed the cylinders by doing a runup? You're joking, right?

 

[ShyFlyGuy]

The manufacturer said that if the chromed cylinders were made excessively hot before break-in (ie. a long runup on the ground), the cylinders will have been glazed. I know I didn't run it up very long, but I can't speak for the mechanic, who had me shaking my head at various points along the way... Yeah, the cylinders are not breaking in, even after 50 hours. Oil consumption, it turns black pretty quick after an oil change, and performance is weak... There is something wrong, and I'm guessing it's glazed cylinders.

Shy

 

[avbug]

As I see your question, there are really two parts. The first is the asked query, which is the safety of continued operation. The second part, unasked, but deserving of discussion, is the issue of the glazed cylinder.

First, you're making a guess as to what is wrong. You cited lacking power and black oil.

Oil consumption, it turns black pretty quick after an oil change, and performance is weak...

The color of oil is meaningless. It's often cited by one source or another as having some significance; it has none. It doesn't mean the engine is dirty, the oil is dirty, there is blowby occuring, the oil is worn out, excessive heat has occured...whatever...it means none of that. It means the oil is dark. Oil color is meaningless. Clear, clean looking oil doesn't mean anything, either.

If the engine has been overhauled or cylinders replaced, then the oil turning black quickly is to be expected, but tells you nothing.

How do you know the cylinders are not breaking in?

What procedure have you used for the past 50 hours while breaking in the engine?

What is your current oil consumption, and where is it going? Have you performed a leakdown test/compression test to verify the leakage source? Has anyone boroscoped the cylinders to check for glazing?

Is it safe? There's the 64 dollar question. As you don't know what's wrong, but suspect something, then answering that your guess might be safe isn't really a safe answer....neither is the guess. If you don't know what's wrong with the airplane, then why continue to fly it? If it's only an improper cylinder break-in, then no, you probably have little to worry about, so far as safety. However, if you have a known problem (which you don't; you don't know what you've got)...then why would you continue to fly without getting that known problem fixed?

You have an unknown problem, and you're lacking performance (but haven't specified what that means). And you're continuing to fly. I submit that this isn't a wise idea. Suppose you have another problem? Aircraft and engines talk to you, often enough, warning you of bigger impending problems. Sometimes that little hint, that lack of power, that creaking, that intermittant problem, whatever it may be, is all the warning you get. You are wise to listen to the warnings, whenever they come, and proceed with caution.

Have you taken oil samples for spectrometric analysis?

 

[ShyFlyGuy]

Oil consumption is a concern. It is burning about a quart every 3-5 hours. We have sent the oil away for analysis, but haven't gotten the results yet. I just flew the airplane, and it climbs like it's got a cruise prop. It does, in fact, have a cruise prop. I would not say the performance is that of a freshly overhauled (if even just a top overhauled) engine. It cruises nice and fast, faster than the average 152 (about 115 kts), so I suspect that the climb performance is due to high density altitude, aircraft loading (two adults and full fuel), and the cruise prop. The major concern, then, is oil consumption.

The break-in process was full power with ashless dispersant mineral oil (whatever it is called) for 25 hours. Oil burn "plateaued" at its current rate. During the beginning stages of break-in, it was around a quart every 2 hours.

Since break-in, it has "fouled" plugs every morning, which is easily rectified by a good run-up and cleaning of the plugs (max power and lean-to-peak). That makes me assume that there is something happening at night with the oil passing the rings.

Compressions are in the low 70's at 50 hours on overhauled cylinders (chromed). That concerns me as well.

Shy

 

[avbug]

I just flew the airplane, and it climbs like it's got a cruise prop. It does, in fact, have a cruise prop.

It performs like it's got a cruise prop and it does have a cruise prop? Perhaps you meant to say it's got a climb prop.

Since break-in, it has "fouled" plugs every morning, which is easily rectified by a good run-up and cleaning of the plugs (max power and lean-to-peak). That makes me assume that there is something happening at night with the oil passing the rings.

Plug fouling can come from several sources, but most commonly from improper mixture usege.

Oil shouldn't be seeping through the rings at all. You don't have a round engine, do you? If you're getting oil in there, it's going to be happening when it's running, and you have two sources; the rings, where oil burns (and will show up as brownish or blackish char deposits on the plugs when you pull them), or it could come through the valve guides. Your engine will be smoking if this is happening.

Oil in the cylinder, within the combustion chamber, will manifest itself as a big cloud of smoke on start. If you're getting oil past the rings sitting at night, then you've severely overfilled the case...by a LOT.

It is burning about a quart every 3-5 hours.

That's not too unusual.

During the beginning stages of break-in, it was around a quart every 2 hours.

Also not unusual.

The usual break-in proceedure will be done as close to sea level as possible. You may need to wear it in; it may be done breaking in. You may want to try going to a muti weight oil, see what you see...you may see a reduction.

If you're still running mineral oil, you've done all the breaking in you're going to do. Time to move away from the straight weight mineral oil, consider going multi weight, and be sure the engine is properly warm before running it up or taking off. If you're running mineral oil, that's part of the reason you're seeing it get dark quickly...again, that means nothing.

You may have a glazed cylinder, but all of them at once, unlikely...and generally it's actually the rings glazing on a chrome cylinder, not the cylinder wall itself. That can be corrected, too. Were new rings used with the chromed, overhauled cylinder.

I don't like chrome in engines. You will have a harder time getting a break-in with them, and higher oil consumption isn't unusual. Low power engines don't do as well with chrome than higher power engines, and lower powered, smaller engines are harder to break in, especially if you're operating at higher altitudes.

 

[ShyFlyGuy]

No, re-read the cruise-prop comment. It was correct. The takeoff performance and cruise performance are both what I would consider normal for a cruise-prop. Climb performance is lacking and cruise is fast. With the climb performance so weak, it just makes one think that it would be attributed to a weak engine. Some folks have reported a 200 FPM climb, while I have experienced no less than 500 FPM, which is almost standard for the book (which was done with a climb/cruise prop, from what I can tell). The book shows 600-720 FPM.

Thank you for the insight on the oil issue. There is no smoke on the start, nor is there smoke once running. I'm guessing that the oil burn that is taking place is little enough to be burned in the combustion. The plugs have not been pulled yet too be examined. I will note the color and any buildup.

While 3-5 hours per quart may not be unusual, I don't like it. I think optimum is around 10 hours per quart, right? We have since switched to 100 weight oil, just the regular stuff (I really need to learn my oils).

New rings, new heads, and overhauled cylinders were used in the top overhaul. I have learned to dislike the chrome as well. In the future, I am going to stick with nickel and steel.

Shy

 

[Mr Wu]

If you are getting 500 fpm climb with two adults and full fuel in a 152 at high density altitude with a cruise prop that gets you 115kts in cruise, you don't have a problem with climb performance. Get over it. What makes you think it was the mechanic that glazed the cylinder when you say that you have to clear fouled plugs every morning by running the engine hot?

 

[avbug]

No, re-read the cruise-prop comment. It was correct. The takeoff performance and cruise performance are both what I would consider normal for a cruise-prop. Climb performance is lacking and cruise is fast. With the climb performance so weak, it just makes one think that it would be attributed to a weak engine. Some folks have reported a 200 FPM climb, while I have experienced no less than 500 FPM, which is almost standard for the book (which was done with a climb/cruise prop, from what I can tell). The book shows 600-720 FPM.

You stated that the airplane lacks performance, and punctuated that by stating that it climbs as though it's got a cruise prop. You then stated that it does have a cruise prop, which ruins your point that it lacks performance...clearly it won't climb like it's got a climb prop, because it doesn't...which leads one to ask what the point was in the first place.

Your airplane is a Part 23 airplane, and the performance numbers are theoretical. No requirement exists that the airplane meet those numbers. Further, in the quote above, you state that the numbers you are seeing "appear standard." Again, this leads one to ask what you mean when you say the airplane lacks performance. Twice now you have stated the airplane is doing what it should be doing.

While 3-5 hours per quart may not be unusual, I don't like it. I think optimum is around 10 hours per quart, right?

How much experience do you have with the 0-235 engine, and in the Cessna 152? Personally I've never seen one go ten hours without a quart of oil, though three to five is common.

Oil consumption by itself doesn't mean anything.

If you're having cylinder leakage problems, then a leakdown/compression test is a diagnostic tool which may allow you to hear the location from which the leakage is occuring. In this case, nothing you've described indicate a problem. You have normal oil consumption with normal performance.

If you have switched to 100 weight oil, what were you using before?

Try a multiweight.

 

[Geronimo4497]

I'd bet a nickel that if you got off the 100W and switched to Aershell 15W-50 or the Exxon 20W-50 that you would see a decrease. The plugs will be a big story teller, as will a good compression check.

I must say that I find it very sad that you blame the mechanic off the bat for glazing the cylinders. What is the field elevation that you operate from? How high did you fly the aircraft during the break in process? Did you touch the mixture at all during break in? It would not be uncommon to foul the plugs during break in because the aircraft should be running at a much richer mixture (ie keeping the engine cool with high fuel mixture). Keep us posted ofter the plug and compression check.