I agree with STOLman above. It is looking increasingly likely that the whole engine is shagged.
At 2.5k TT and 1k since a top overhaul, it’s time for a complete overhaul, by some reputable shop which does this 24/7 for a living. If it was me, flying over the Alps etc, I would ship it to the USA. It’s just a pity to be doing this at the start of the summer, and even more so on the rare TIO-540 B1AD in question here which is expensive to overhaul.
One way to quickly damage a cylinder is to have uneven cooling. The cylinder gets out of round and bad things happen. Baffles are important and sometimes counter-intuitive.
I am quite annoyed at this stage as the shop did not perform the easiest check to swap the probes, instead they checked the fuel metering on all cylinders.
I have talked to my FAA I&A and he said that this sounds like the exhaust valve not closing properly and to check the lifters. When I spoke to the shop about this their interpretation of a valve not properly closing would be lower egt temps due to imperfect combustion. Makes also sense but who is right on this?
Unfortunately, the shop did not check the cam when the cylinder was pulled as he did not expect this scenario to happen.
Could it be that if exchanging an ECI cylinder for a Lycoming the lifters would have to be exchanged also?
Two years ago I had to pull cylinder 6 and then Gomolzig in Siegerland looked inside as much as they could see and found no corrosion. I sure hope it is not the cam.
I can not think the circumstances when having removed a cylinder I would not inspect the cam, in my view not inspecting the cam is negligent.
I am starting to think that this is an exhaust valve being held open and I have to ask if on re-assembly the hydraulic lifter was bled and the dry valve clearance checked, I was assuming this was done until it was mentioned that the cam had not been inspected.
My FAA inspector also think it is an open exhaust valve but my mechanic says this would yield lower egt temps so I don‘t know who is right. The whole saga has started on the wrong footing. I had a rough running engine on one magneto so we thought it was an ignition issue. The spark plugs got checked and found good so we sent the magneto that was overhauled less than 6 months ago and had maybe 20 hrs back to the overhaul shop for testing. It came back with no fault found. After checking the harnesses they performed a compression check and found the burnt valve. Until then I had no issues with my temperatures, the engine ran as smooth as a Lycoming can run and from today to tomorrow by exchanging a cylinder the cam should be the cause?
Instead of first checking the probe they looked at the fuel delivery and found all good. I had asked to first exclude an indication error. The next thing they will now do is swap the probe, then check valve seating and dry tappet clearance. Eventually they should check the paperwork if the overhaul shop really sent the correct cylinder assembly.
I cannot believe the cam yielding such a result overnight.
My FAA inspector also think it is an open exhaust valve but my mechanic says this would yield lower egt temps so I don‘t know who is right.
A partly open exhaust valve would cause air/fuel mixture to burn in the exhaust yielding higher than normal EGTs. I have a graph showing what happens when an exhaust valve sticks fully open, then partly open, somewhere. When the valve is fully open there seems like there is little or no combustion at all and EGTs are lower supposedly because there is little or no compression. If the valve is partly open, burning gases escape into the exhaust and there is a marked EGT rise. That will pretty quickly burn the valve too.
I cannot believe the cam yielding such a result overnight.
Me neither. A can cannot cause just one valve to open prematurely or stay open.
Just a wild guess, are you sure the correct cylinder/piston combination is fitted?
That would be a good one! This TIO540 has a lower compression ratio than the IO540 on a TB20.
The scenario outlined above by STOLman should not be discounted. Unfortunately, with no oil analysis, there is no way to check apart from pulling the cylinder again. One could do oil analysis on the existing oil if it has reasonable hours on it, say >10.
Eliminating the EGT probe is the #1 job, but something must have made the previous cylinder seize up and that may still be present.
Quote “Me neither. A can cannot cause just one valve to open prematurely or stay open.”
While I agree with this statement I think something has been missed here, when you change a cylinder it is vital that you bleed the hydraulic lifter as this expands to full extension and won’t retract without being bled. Once the new cylinder is in place it is required to check the dry valve clearance ( this can be adjusted if required by changing the pushrod ) .
I have seen an O-360 wreck it’s self very quickly after a person who was not qualified and did not understand hydraulic lifters change a set of cylinders, the Engine ran just long enough to get to 2000 Ft.
My suspicion is that when cylinder was changed an error was made with the bleeding of the lifter and dry valve clearance and the valve was only just shutting, when the engine got hot and expanded the valve was lifted slightly off its seat and was partly open all the time, with very hot gasses passing around the valve the gap will quickly expand as the valve & seat burn out.
A_and_C wrote:
While I agree with this statement I think something has been missed here, when you change a cylinder it is vital that you bleed the hydraulic lifter as this expands to full extension and won’t retract without being bled.
I think your suggestion, which you already made in post #45, is the best one so far. I suppose one could confirm the valve does not close by performing a cylinder compression check, and take it from there.
