Drained two tanks of fuel chasing a engine surge on a 172

I spent three full afternoons troubleshooting a rough-running Lycoming O-320 on a Cessna 172 at our local FBO in Wichita, swapping plugs, cleaning injectors, and checking mag timing with no luck. Turns out the number three cylinder had a stuck valve from lead buildup, and the whole thing took me 14 hours before I finally gave up and borescoped it. Has anyone else burned way too much time on something simple that should have been obvious from the start?

3 comments

3 Comments

wesley18128d agoMost Upvoted

Man I get what you're saying but honestly I used to be the guy who would throw parts at something like that for days before grabbing a borescope. I was convinced it was always a ignition or fuel issue so I'd chase those forever. Then a old timer showed me how lead buildup can stick valves on these Lycomings and I felt like an absolute idiot. Now I borescope any rough running engine before I touch anything else. It just makes sense to look first instead of guessing for 14 hours.

anthony_campbell8828d ago

Wesley's right about borescoping first but that number three cylinder thing is actually pretty common on the O-320s - lead fouling hits those middle jugs first because they run cooler.

emma_dixon7028d ago

Is it just me or does this same "skip the basics and chase ghosts" thing happen in all kinds of repairing stuff? I've seen guys replace entire brake systems on their cars when the real issue was just a dirty master cylinder bleed screw. We always think it has to be the complicated expensive problem first (you know, ignition or fuel), when usually it's the simple stuff hiding in plain sight that bites us.