airguy
Cleared for Takeoff
I've got a 2001 model C172 with IO360 and FP prop, GAMIjectors and full engine monitoring. I've put 300 hours on it in the last 15 months and the longest it ever sits would be about 2 weeks without at least a quick joyride somewhere. Always run 100LL, always flown WOTLOP cruise, almost always taxi very lean, engine total time now 1100, was bought a couple years ago at 600.
This past Friday it flew about 5 hours in two legs roundtrip, then I took it 20 minutes away to a fuel stop, self-serve quickturn, 10-15 minutes total downtime. After fueling I did a normal uneventful hotstart, taxied about 4000' to the runway with mixture mid-range to full rich, I forgot to lean it for this taxi. At the runup area I did my normal mag-check and #3 cylinder was completely dead - on both mags. I had not noticed any vibration in the engine during taxi, but I also never got above 900 rpm so may not have noticed it in any case. I ran the engine at about 2000 rpm with it leaned to the stumbling point and after playing with it for about 2 minutes #3 finally came back onboard. I taxied back to the hangar and pulled all the plugs, found some minor lead fouling but nothing I would consider out of the ordinary (sorry, no pics...). I did not do a compression check, but I buttoned it all back up, did another mag check and full-power static RPM check (2380, right at normal for this plane under these conditions) and all checked out good. It flew another half hour home without issue and I put 4.9 hours on it the next day, no issues. I did several in-flight WOTLOP magchecks at altitude with normal results.
My question is this - I've heard of "morning sickness" on the Lycomings where you can have an exhaust valve stick on a cold engine at startup, and after warming up it releases and all is normal. This was an already warm engine that was only shutdown about 15 minutes so would not be a cold-block scenario. The fact that ONE cylinder had BOTH plugs go bad and all others were fine is not an impossible-odds scenario, but it's beginning to get a little far-fetched. I'm wondering if I had a valve guide sticking on #3, but I've only heard of this occurring on a cold start, not a hot start. This engine is approaching midtime, consumes one quart in about 10 hours, is run regularly and has never given any hint of unhappiness until this little hiccup. I don't believe I had an injector plugged because while working it with #3 dead, it was backfiring and popping - which tells me unburned fuel was getting out to the exhaust and igniting, which means the injectors were flowing. When this happened Friday it was hot and density altitude was about 6000' on the ground - if I taxied at full rich for 2 minutes it's entirely possible I could have fouled the plugs, I just find it unlikely I would have fouled both plugs on one cylinder and no other plugs.
Any suggestions? Annual is coming up in June.
This past Friday it flew about 5 hours in two legs roundtrip, then I took it 20 minutes away to a fuel stop, self-serve quickturn, 10-15 minutes total downtime. After fueling I did a normal uneventful hotstart, taxied about 4000' to the runway with mixture mid-range to full rich, I forgot to lean it for this taxi. At the runup area I did my normal mag-check and #3 cylinder was completely dead - on both mags. I had not noticed any vibration in the engine during taxi, but I also never got above 900 rpm so may not have noticed it in any case. I ran the engine at about 2000 rpm with it leaned to the stumbling point and after playing with it for about 2 minutes #3 finally came back onboard. I taxied back to the hangar and pulled all the plugs, found some minor lead fouling but nothing I would consider out of the ordinary (sorry, no pics...). I did not do a compression check, but I buttoned it all back up, did another mag check and full-power static RPM check (2380, right at normal for this plane under these conditions) and all checked out good. It flew another half hour home without issue and I put 4.9 hours on it the next day, no issues. I did several in-flight WOTLOP magchecks at altitude with normal results.
My question is this - I've heard of "morning sickness" on the Lycomings where you can have an exhaust valve stick on a cold engine at startup, and after warming up it releases and all is normal. This was an already warm engine that was only shutdown about 15 minutes so would not be a cold-block scenario. The fact that ONE cylinder had BOTH plugs go bad and all others were fine is not an impossible-odds scenario, but it's beginning to get a little far-fetched. I'm wondering if I had a valve guide sticking on #3, but I've only heard of this occurring on a cold start, not a hot start. This engine is approaching midtime, consumes one quart in about 10 hours, is run regularly and has never given any hint of unhappiness until this little hiccup. I don't believe I had an injector plugged because while working it with #3 dead, it was backfiring and popping - which tells me unburned fuel was getting out to the exhaust and igniting, which means the injectors were flowing. When this happened Friday it was hot and density altitude was about 6000' on the ground - if I taxied at full rich for 2 minutes it's entirely possible I could have fouled the plugs, I just find it unlikely I would have fouled both plugs on one cylinder and no other plugs.
Any suggestions? Annual is coming up in June.
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