Successful 201 Forced Landing

[LBM]

On 4/26/2025 at 10:50 AM, Yetti said:

Seems old enough to be of the time they were switching from old valves that would break to sodium filled valves and such.  Might look for an SB or AD

It’s getting overhauled, with four new Lycoming factory jugs.  That plus age make root cause purely academic as far as I’m concerned, so not worrying about looking for any AD or SB.

I would like to know more about the “old valves that would break” as I’ve heard such comments before.  I’d especially like to know if there was possibly any kind of embrittlement or metal fatigue contributing to a propensity for breaking.

On 4/26/2025 at 1:24 PM, A64Pilot said:

Sodium filled valves have been around for a while, the engine in The Spirit of St. louis I believe had them for example.

https://airandspace.si.edu/collection-objects/wright-whirlwind-j-5a-b-radial-engine/nasm_A19791508000

Most valves are two piece that is the head and stem, often if there is a failure it’s at the joint, most often a failure results from the piston hitting the valve, as they aren’t aligned this bends and sometimes breaks the valve, on aircraft I believe the most common reason for the piston to hit a valve is a stuck valve, very rarely I guess it could be a broken spring etc.

‘The piston staying in one piece is rare I think, often it gets broken, rod goes through the crankcase and of course the engine stops, if yiu break a valve and the engine keeps running, buy a Lottery ticket, because that was your lucky day.

Those were pretty much my thoughts.  No broken valve spring observed.  There had been none of the classic evidence of sticking valves, i.e. so called morning sickness etc.  At most very infrequent evidence of fouling found at mag check, always easily cleared by leaning to burn it off at high RPM.

The engine was alleged to be in service for about 1100 hours since it was overhauled, but on careful review I do not believe it was truly overhauled at that time;  rather I believe it was IRAN subsequent to a prop strike.  I’ve not thoroughly analyzed the log entry to identify all parts identified as replaced.  I’m suspicious that valves and valve springs may not have been replaced at that time, and could possibly have as much as 2000 to 3000 hours time in service.  Or even as much as 4140 hours, as that is the engine total time.  They were certainly over 35 years old, perhaps in their forties.

I once lost a car engine when the throttle stuck open on starting and it overrevved, causing valve float before I could react.   That’s why I don’t trust valve springs, especially old valve springs, and that’s one of the main reasons I don’t believe in running far past TBO even if the engine is not making metal.  This wasn’t running high RPMs, happened in cruise at 23.5 squared, but I assume the valve springs may have been getting tired and lazy.

My hypothesis is that the valve may have stuck or floated due to a lazy valve spring and the head got knocked off by the piston.  Age of the valve may have contributed, if it work hardened and got brittle because service life was exceeded.

Regardless, it won’t matter now.  That’s why I choose to do the full overhaul and put four new factory cylinders on it.  It’s also why I chose the engine shop I did instead of going with a local shop.  I’m doing everything I can to ensure that I have only known good components going forward.

Edited May 7, 2025 by LBM

[Yetti]

one thread about valves.