I had an interesting day today. I was in a school 172 flying with my student in our local practice area doing maneuvers when a loud bang gets my attention immediately followed by violent engine vibration and loss of RPM. I look down at my engine instruments and oil pressure seems constant. The engine however feels as though it's making half power at best surging from 1000-2200 RPM. My immediate thought is the engine is compromised and I need a field. Off my side I see a decent field with some dirt roads in between oriented east into the wind. I head to the field and circle and try to think through my options. I am able to maintain altitude and notify approach of the situation. They clear me direct to the field which is approx 25 miles away. I do another circle and reason I do not feel comfortable flying the plane back over a populated area when unsure about the engines integrity. So I commit to making the precautionary off airport landing which is uneventful with no damage to the a/c. After I inspect the engine cowling I clearly see a bent push rod and oil loss. I wait around for the school mechanics and the fsdo safety inspector who checks the plane quickly then lets the mechanics do their thing. This was my first actual power plant related emergency. Just interesting to me how you get into such a groove of normality with instruction that you start to think that these types of occurances are few and far between but they do happen. I'm just glad it wasn't a total power loss and that my student, the plane, and myself are safe.
Nice Job! Glad you're ok. Sounds like you kept your cool, kept your focus, and made a good decision.
As I read your first four sentences, and was almost certain your 12th sentence was coming. I had
precisely the same thing happen -same model, same jug- during a delivery flight. Mine was in a foreign country where ATC English did not extend to off-script events, and an off-airport landing would likely have been worse than a crash. That added a bit of spice to the dish, but same recipe.
Who'da thunk the vibe from a bent push-rod could create such a fracas and caterwauling? I initially thought the engine was going to depart its mount.
When did it happen? Just randomly in flight? Or in response to a change or input? Mine happened as I reduced power for initial descent out of a long, high cruise.
Our problem resulted from crap fuel. Yup, I checked it. Yup, it smelled funny. Yup, I had doubts. But also, yup, it was the ONLY option available. I ended up replacing the whole jug. I'd advise you look into that. Simply replacing the push-rod is likely insufficient. Also, be glad you had your problem in the US; Maintenance on an N-reg in certain international locations is a serious PITA.
EDIT:
Your mechanic sucks if he thinks just replacing the push rod will do it.
@Roger Roger is correct. Bent push-rods almost always happen because of bad/stuck valves - or something worse; rarely, if ever, is it just a bad push-rod.
