HeyChuck

This engine has now had 5/6 of a "top overhaul" in the past couple years (5 out of 6 cylinders overhauled)...the crankshaft and camshaft are still looking good. I considered doing a major overhaul last year, but there were parts availability problems and delays at that time, not sure if that is still the case. Maybe next year...

Thank you for your suggestions and getting input from George Braly. I will take the plane to a shop Wednesday to check the plugs, other cylinders, etc.

This is a close-up of the top of the piston in the 10-noon area. The rough spots are built up deposits, not erosion features.

Picture of the piston in profile from "10 to noon" aspect. Doesn't feel like melting or erosion around the piston crown to me, but I don't have a lot of experience with this.

Attached is a close-up picture of the extracted exhaust valve showing two through-going cracks on the valve head that are tangential to the stem. The picture of the piston shows more deposits on the top; I was told it is fairly common to see more deposits where the fuel comes into the cylinder as it is cooler there. Not sure about detonation because the intake valve and piston don't appear damaged, and the CHT stayed below 400 F.

A couple other mechanics I have shown this to had a similar thought. No signs of the classic asymmetric burn pattern that sometimes foretell a failure.

Oil consumption was normal before the failure. Maybe the valve started sticking some in the guide and was burnt with blowby?

I will do that next time. Thanks.

The cylinder compressions were not the concern. The cylinder with 55/80 compression had a leaking exhaust valve but was not burned. More importantly, there was some modest delamination of the Nickel plating on the cylinder wall, which could have progressed and caused further problems. The inspecting IA thought he also saw some anomalous wear on the wall of the cylinder (with 70/80 compression) during borescope inspection, so that cylinder was also replaced. That was likely unnecessary because the minor pit appeared insignificant upon closer inspection.

That is an interesting possibility. The mechanic visually inspected the cam and lifter while the cylinder was off, but didn't remove the lifter to test integrity. I don't think any anomalous lack of pressure was noticed when the lifters were bled down during cylinder replacement, but maybe nobody was paying much attention to that.

Yes, the plugs, rings, and piston were all fine. The busted valve is still in the removed cylinder, I may take it out for closer inspection.

Getting on with it.Because I was far from my home base, it was more expeditious to replace the entire cylinder assembly & piston (even though there was no other damage), then fly home (a week later). Fortunately, the IA who inspected the turbocharger found no damage, so the pieces presumably exited through the exhaust pipe.

I was not present when the compression was tested during the annual, but the IA stated "Checked compressions: orifice psi 46, #1-55 #2-80, #3-80, #4-70, #5-79, #6-80." Cylinders #1 and #4 were subsequently replaced. The valves on cylinders #2 and #6 were replaced about 200 hours previously.

The exhaust valve in a cylinder of my Continental TSIO-360SB failed during flight (at 1554 hours SMOH). The engine ran rough and cylinder went cold; landed ASAP. The attached picture of the broken valve was taken after we removed the cylinder. This cylinder had compression 80/80 during the annual inspection 24 hours earlier, with no signs of burning during bore-scope inspections. No obvious CHT or EGT anomalies on my JPI EDM-700 were noticed before the failure, but the data were not being recorded. Has anyone seen a valve fail like this?

Possibly. It is also possible that a complete teardown will reveal no problem with the lower end. Although 1/10 teaspoon (total volume) of probable cylinder-plate metal was found in the sump, this engine has been very reliable, and currently has excellent cylinder compression, clean oil analysis indicating normal wear, relatively new starter, spark plugs, magnetos, alternator, etc. A Continental engineer thought the flakes likely came from the base of a cylinder during break-in, and advised not to pull any cylinders yet. They may also have worn during a cold, "dry" (minimal lubrication) start. Safety is paramount. Because engine failures are more likely to occur after major maintenance (top or major), careful diagnosis and targeted remediation is the conservative and safer approach than immediate tear down. A long ground-run with subsequent filter and sump inspections should come first. Perhaps removal of one cylinder will enable borescope inspection of the other cylinder's walls that couldn't be seen from above the pistons. Regarding overhauls: Penn Yann and Western Skyways declined to quote because they cannot overhaul within the next year (think supply-chain issues) and/or parts availability and prices are too uncertain. Continental likely has best access to parts for overhaul; Continental quoted $87,258 and 7 months for a factory reman. The least expensive "field overhaul" I have been quoted is over $50K (about $60k with removal/installation, hoses, etc.) with a 6 month turn-around. Others are more expensive with turn around times on the order of 7-8 months, IF they can obtain parts.