It's a 5k$ part ya know!

[Capt. Timeter]

Right after takeoff, and that thing just failed on me! And it hadn't even 100 hours on it!

cyl.jpg (181.74 KiB) Viewed 381 times

Now, whom am I referring to for the warranty?

Okay, if we get serious...

1. What exactly is wrong with it? I suppose a cylinder head blew off?
2. Why could it have happened and how could I have prevented it? This was the newest cylinder in the set and it never got even close to the limits. Along with the No.2 it's among the coldest.
3. How long does it take IRL to replace a cylinder on O-540?
4. What is the proper procedure to break in a new cylinder when I replace this one?

[AKar]

1. What exactly is wrong with it? I suppose a cylinder head blew off?

With that description on the tablet, you'd probably have rather bad piston rings and probably the piston itself as well. Not sure how precisely, but...somehow. If you blew a head off, the likely outcome would be a loud pop and debris from the cowling and said head flying out in the corner of your eye just as the windshield (if installed) turns opaque. I'd doubt the engine would keep running at all, but if it by some chance did, I'd still prefer exercising my gliding experience over ad-hoc on-job training in in-flight firefighting.

In reality, if you simply completely lost compression on a cylinder without any other mayhem, perhaps the likeliest find with a borescope would be a damaged valve. (If on a turbo, you'd of course start worrying right there how well the turbine's teeth handled the chewing.)

2. Why could it have happened and how could I have prevented it? This was the newest cylinder in the set and it never got even close to the limits. Along with the No.2 it's among the coldest.

Probably nothing could have been done to prevent it. While perhaps somewhat dubiously omnipresent in A2A fleet from what I gather from looking the internet (I'm yet to encounter anything catastrophic myself), aircraft tend to have some bathtub curve applicable on them in real. It is a long and controversial story why, but generally speaking, most things hand-fitted and with wide tolerances take a brief moment to figure it out if they want to work together or not. And also, not many things get better by being taken apart and back together, thus, an elevated likelihood of issues would be there after any work done. However, I can't really see what the tablet states there to be a likely outcome of infant mortality.

3. How long does it take IRL to replace a cylinder on O-540?

Speaking generally of any O-engine, with or without prefixes, not that long on its own. Gaining access in some cases, and getting stuff of the hat off and what not would take some time, but I'd say all included it would be roughly a day's job, old out and new in. Anyways, if we took the tablet's word for the initial diagnosis, I'd be worrying more about entirely different things.

4. What is the proper procedure to break in a new cylinder when I replace this one?

It would not make a difference at all in the sim, as far as I understand, but you'd run it fairly hard for several hours until "oil consumption is stable". The engine manufacturers' publications detail their view of the correct process. How big a difference at all that makes, and whether you should be running the engine that fairly hard all the way beyond the break-in, is a bit controversial. My personal view is that babying the engine is not generally required and sometimes even counterproductive, the break-in period being very specifically one of those times.

-Esa

[Capt. Timeter]

if we took the tablet's word for the initial diagnosis, I'd be worrying more about entirely different things.

That's interesting! What things exactly? A broken valve, you said?

Yes, a blown head is unlikely. There were neither debris nor any particular noise. It just started to run a bit rough as if I overleaned. Trying to amend it by enriching and finding no help I then noticed the temperature going down for landing before I decided to do this with the rest of the aeroplane It actually ran somewhat tolerable until the very landing at reduced power with some vibration, but yet I was in a hurry afraid of a more serious failure that could follow. By the way, inspection has shown no significant decrease in the amount of oil, thus I concluded the oil system wasn't damaged.

[Michael-C172pilot]

At our flying club we have 3 IO360s for our C172 and one O-360 for our Piper Archer 28. Since we fly around 1000 hours/year, the planes usually get between 150 to 300 hours/year, so after around 8 years the engine needs overhaul. We fly them "on condition" until something is wrong, and the bathtub curve is really spot on - I personally have less issues flying an engine with 2000 hours than being the guy who flies the engine in the first 20 hours - although we so far didnt have any big engine trouble in recent years either (undfortunately we had a fatal accident 20 years ago, but this was a Piper 28 where one tank was full and one was empty, and he tried the impossible turn and stalled with 100 litres of Avgas burning in front of his girlfriend standing at the airport - so, in many cases, engine failures are actually caused by fuel starvation or contamination and much less likely ignition/valve/cylinder issues.)

What we do, however, is use special break-in oil for the first 25 hours. This must not be mixed with regular engine oil, but I do not really know which type it is. Apart from that, we demand pilots to fly at least one hour in the first 25 hours of the new engine, no traffic patterns. Whether this is really necessary, I cannot comment on.

[AKar]

if we took the tablet's word for the initial diagnosis, I'd be worrying more about entirely different things.

That's interesting! What things exactly? A broken valve, you said?

Well, to simply share my line of thinking, if the combustion chamber and the oil pan suddenly made an airpath connection through the piston and/or the rings, as suggested by the message there, the stuff originally having had a task of sealing that path must have gone somewhere. In an environment where the piston lives, that would mean an assorted collection of fairly finely ground, and perhaps molten in part as well, metal debris blown into the crankcase. In and from where it would get into places where having it in is not okay.

At our flying club we have 3 IO360s for our C172 and one O-360 for our Piper Archer 28. Since we fly around 1000 hours/year, the planes usually get between 150 to 300 hours/year, so after around 8 years the engine needs overhaul. We fly them "on condition" until something is wrong, and the bathtub curve is really spot on - I personally have less issues flying an engine with 2000 hours than being the guy who flies the engine in the first 20 hours [...]

The presence of bathtub curve should, for any engineer and put simply, mean that something is not done right. This is, however and unfortunately, the state of aviation as far as I've gotten and still have got a touch for it. It is also a thing in the airliner world. But I guess the economics of everything have balanced it where it is.

What we do, however, is use special break-in oil for the first 25 hours. This must not be mixed with regular engine oil, but I do not really know which type it is. Apart from that, we demand pilots to fly at least one hour in the first 25 hours of the new engine, no traffic patterns

Yes, the recommendation is to run with straight weight, non-AD (ashless dispersant) mineral oils for break-in. (For non-turbocharged engines, that is, whereas the turbocharged ones, by some magic, break in fine with oils recommended to not primarily serve the break-in but proper functioning of the controls.) These are also referred into as 'grinding oils' by some. I think that gives out the idea, of benefiting from the oil perhaps not carrying away the wear and dirt particles as well as it possibly could.

It all makes (some) sense, but whether or not it makes a proper difference, I don't know.

-Esa

[Capt. Timeter]

Well, to simply share my line of thinking, if the combustion chamber and the oil pan suddenly made an airpath connection through the piston and/or the rings, as suggested by the message there, the stuff originally having had a task of sealing that path must have gone somewhere. In an environment where the piston lives, that would mean an assorted collection of fairly finely ground, and perhaps molten in part as well, metal debris blown into the crankcase. In and from where it would get into places where having it in is not okay.

I see what you mean. Then it's an oil change with everything that follows and also a crankcase inspection... Sounds like more than a day's job

Michael
That's a terrible story. I can't even dare to imagine what would happen to my girlfriend if I crashed like that in front of her.

[Michael-C172pilot]

Yeah, a lot unfortunate developments happened that day. He filled up one tank and took off on the other one to fly 3 patterns (90 day rule- you may only take Pax on Board if you had 3 landings within the last 3 months) so they could fly together after that. One of the unfortunate Design decisions of many low wing planes that you need to shift tanks. And unfortunately it went empty just after takeoff and in EDLH at rw 24 there is not much you can do.

Could have been avoided by adhering to the checklist.

One of the reasons I like the A2A planes. You can really train procedures.

[Capt. Timeter]

Yes, the recommendation is to run with straight weight, non-AD (ashless dispersant) mineral oils for break-in.

I guess it's the 100AW oil in the Accusim. However, looking at its characteristics I conclude it's suitable only for summer temperatures.

[AKar]

Yes, the recommendation is to run with straight weight, non-AD (ashless dispersant) mineral oils for break-in.

I guess it's the 100AW oil in the Accusim. However, looking at its characteristics I conclude it's suitable only for summer temperatures.

Well, not really. I was a bit careless in my words there; straight weight is not really the main point (even if that's very much what the break-in oils usually are), but straight mineral is. Nomenclature is a bit weird here, but most modern (well, "modern") oils, including that 100AW, are called ashless dispersant to differentiate them from straight mineral oils that lack certain additives. Which, under higher than normal surface temperatures associated with the abrasive break-in process of the cylinder wall, as theory goes, can "form a glaze in the honing grooves on the surface of the cylinder wall. [...] If this glazing of these honing grooves occurs before the break-in period is complete then the piston ring will not seal properly, and the cylinder wall will no longer have the surface grooves necessary to carry lubricant, and the combination will result in a poor gas seal and high oil consumption." Quoting AeroShell there.

We did not have this stuff around when I was more directly involved with things, but you can apparently find multi-grade non-dispersant oils as well. I did not comb through the specs, but break-in is suggested there as an application.

-Esa