I have chronicled my data in this thread. Result of a customer leaning his Carbon Cub SS in cruise flight how he had done his old Cessna for years and ended up burning an intake valve. Bobby Loper at ECI was a good source on the ignition and leaning conclusion.
Steve, great thread and thanks. Nice to get some in depth info on the care and feeding of a Lightspeed ignition and what can happen with its use etc.
Short but to the point story on an intake valve failure of a bit larger proportion but just points out how much a bad intake can affect an engine. Pretty much apples to oranges engine wise but similar results. It’s just an engine after all.
Dead of winter about 1978 or so…C-46 tanker delivering heating oil 2K gallons a pop along the lower Yukon. Our old high time pilot Bob Rice in cruise but setting up for landing in Galena, done for the day. Cold, probably -30 or so, getting close to entering downwind and starts power reduction for gear extension. Gear still in the well when #1 (R-2800) backfires so violently it belches whitish blue fire out the intake scoop that reaches as far forward as the rear cockpit windows. That’s about 6-8 feet. Not once but at least 6 or more times so fast it was like a machine gun. Only quit when Bob pulled the throttle back in a huge power reduction. Gear down, mostly routine landing from there but engine definitely not doing much at that point. Airplane parked, called the boss, mechanics dispatched (myself and the bosses son).
Took some investigation but end results were: #8 (master rod cylinder) zero compression due to intake valve head missing, valve stem punched through the top of the head between the two valves, massive hole in the piston where the valve head had exited into the crankcase. Garbage engine, all in less than about 30 seconds. The interesting part, as was the case with the CC 340 engine, was the complete multiple ignition event of what amounted to the entire intake charge for the entire engine at once, in rapid succession, though the valve head wasn’t gone on the Lycoming and much less being ignited. Interestingly, while that was going on, it was also torching out of the crankcase breather line (1”) and burning a nasty spot on the tire that was just coming out of the wheel well. Got it hot enough to crispy a spot enough we had to change that tire also. Intake system compromised: definitely not a small problem. I’ll take a “routine” toasted exhaust valve any time over that.
Cheers, Mike