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Although #2 is typically the one that becomes stuck it's not 100%. #1 and #2 are typically the hottest of the 4 so #1 can obviously has and can occur. Phillips 20W50 does seem to be a common element? BTW unless your CHT is also backwards (possible) # 1 is # 1.
Don’t fix what isn’t broken. If they pass the wobble test, you’re good. There are lots of reasons a cylinder can temporarily go dead.
+1
Sure, Wobble test first. I open to hearing what else could make a cylinder go completely dead.
Spark, air, fuel. Take any one away and the cylinder goes cold.
It is far more common for valves to stick when the guides are cold vs hot. Of course, the latter can happen, but I would not rush to assume a sticking valve. Many other things can create similar symptoms. This bears repeating, DO NOT ream a guide until you have confirmed too small of a clearance.
Need adequate airflow, proper fuel quantity, compression, and spark. A piece of carbon can break off and get stuck between valve and seat, preventing compression, just like a stuck valve. These also clear quickly and resolve as stuck valves often do. If a valve sticks when at peak temperature, it is far less likely to release itself, as it does when cold. Typical presentation is guide shrinks when cold and valve sticks. As the guide warms up,m it expands and releases the valve. Not universal, but typical.
I believe that is his MAP, maybe a picture that doesn’t cut off the moment he looses the cylinder transition would help.
My mistake, I didn't realise that was MP. I still believe you're more likely to have had a fuel blockage than an exhaust valve stick at a steady phase of flight
Especially when running Phillips 20W50 it seems. I switched to Aero-Shell 15-50 that contains Lycoming LW 16702 antiwear additive already for my IO390 about 400 hrs. ago and the surfaces around the valves seem to be cleaner now with less signs of black specs. The Phillips oil seemed to stay "cleaner" longer but made me wonder where the dark deposits are going if not in the oil. The 390 I have a very difficult time seeing down into the valve stem guides. My PV 540 is much easier. I also have and continue to change the oil every 25 to 30 hrs.
Looks like you experienced a 100% power stoppage in that cylinder and slight fuel flow decline followed by an increase in MAP and FF to the other cylinders? There are other more experienced than me but if it was a fuel issue your spider would need to clog almost 100% immediately to do this and then 9 secs later cleared the clog and return to normal fuel delivery? The graph above (my previous post) represents an injector malfunction that essentially stopped fuel from entering the cylinder and thus the cylinder immediately went dead and stayed dead the remainder of the flight.
When one of 4 injectors becomes restricted, the other three get the extra fuel and they go rich. OP was lop at the time and at the event, the other three egts rose, indicating enrichment. This adds support to the possibility that fuel flow was the culprit. Far from definitive, but plausible. A stuck exhaust valve creates a new source of air for all cylinders on the intake stroke. This air does not go past the servo, so no additional fuel added for that airflow. This should cause leaning on the other three cylinders, yet they got richer. This would also raise map, which we saw in first graph, but could also be caused be various other thing triggered at that time. This somewhat points away from a valve issue. Again, not definitive.
I disagree. Very slow egt decline and very slow recovery. This was not a stuck now release later event, as you would see sharper lines. Egt also only dropped to 600, so some combustion still occurring.
It looks to me his EGT took 9 secs to fall below 600 F. Mine took 11 secs to fall below 600 F after a confirmed stopped injector. These cylinders don't cool off that quickly given others are producing power and heat. You have data that supports one cylinder can cool quicker (or heat) faster than these?
Your right. As I look at the data again I see a rapid drop. I was looking at a different chart and must have misinterpreted the numbers as I thought I saw 20+ seconds.
Note that Phillips AW 20W-50 has the LW 16702 additive, X/C 20W-50 does not.
Most modern oil starts to break down and oxidize around 260. Unsure at what temp it becomes coke, but suspect 350+. A better experiment is to heat the pan to 350 or 400/and let it cook for a while. Suspect you will find a hard blacl layer of coke on the bottom after some time.
sorry for the ignorance but what does morning sickness feel like? i can’t say my engine idles smoothly when it’s in the 40 or 50s oat until it warms up. but it’s not OMG-something-must-be-wrong rough. at about 1000 rpm it runs normal. is this considered “morning sickness”?
No. More likely too lean on idle mixture if it doesn’t do that in warmer temps. Morning sickness involve one of the cylinders going totally or partially cold. Running on three cylinders is rough and can’t mistake it for unsmooth idle. It is theOMG thing. However, sometimes it sticks in a position where things can combust a bit creating variability in the roughness. I don't believe the symptoms will be the same in every case.
So, if I am reading this correctly, the stem of a sodium filled valve is over twice as efficient in transferring heat out of the stem and leaves the middle portion of the stem hotter than a traditional valve. so, am I correct in assuming this would in theory transfer more heat to the guides and make the guides hotter and therefore more likely to coke or am I misreading this? If we are more efficient in transferring heat to the guides, then the guides must also be more efficient in shedding tha heat.
That's correct. I think the big picture theory is that you can run hotter/harder without melting the valve. But that assumes sufficient cooling available in the head. I don't have direct experience with these engines, but I gather from reading that oil flow in the head is rather anemic. Sufficient for lubrication, but perhaps not enough volume to do any significant cooling work.
That has been my theory for years and have pontificated on that here several times. Oil is a great heat shedding tool and most engines shed 25-30% of their combustion heat via oil. Most every auto engine sends a good quantity of oil via the pushrods to cools the valves, yet lycoming does not. Still believe this is why sticking valves are seen frequently on lycomings, but never on the thousands of other engine types. However, maybe it is not that alone causing the problem. Dans post here has me wondering if lycoming made the problem worse with these sodium filled valves. We are already struggling with too much heat around the guides and here we more than double the heat load. We all look at chts to determine how hot the head is, but unsure if that heat is uniform. The temp probe sits in the center of a large mass of metal, yet the guides are in very thin metal offset from that mass. What if things are much hotter in the metal surrounding the guides. Maybe that area relies more on nearby cooling fins to shed heat. Now imagine each plane with unique baffling setups with all different kinds of turbulence in that area and it possibly begins to explain why two identical engines have such different sticking problems.
I started designing one but never had the problem, so never implemented. Basically creating squirters in the rocker box pointed at the exhaust valve. Can easily tap in to the two main oil gallies via the fwd 1/8” plugs. Never did the engineering to determine orifice size, but would guess something around.020” would be fine. You could take the orifice size of the std lyc piston squirters and reduce by about 30-50%. Don’t need a huge amount of oil here.
+1 on that.
agree that lyc could care less. Possibly not a total lack of concern but more about the liability consequences of making changes to design.
We dont have a dog in this hunt, but surely seems like its time for a new design engine.
