Sticky Valve on Front Engine

Dale Campbell · #1 01-03-14, 01:10 PM

Has anyone had a valve stick open at high RPM on I/O 360 normally aspirated engine.
I have a valve that opens and closes fine at idle, but at high RPM my #4 on front engine sticks open. It happened just before annual and the mechanic did not get it solved. He added something to the oil and said it would free it up. It did for a few flights and now the problem is back. I have a Insight CHT/EGT and the #4 jug shows 350 degree and exhaust shows 1250 degree at idle. At normal flight 2500 RPM and above #4 head temp drops to 90 degree and exhaust reads 120 degree instead of normal 1350 degree like the rest. He changed all 12 spark plugs, check mags, compression is 78-LBs on all cylinders and cleaned fuel injector. I flew yesterday for 2 hours. The first hour all was good. I landed for fuel at Lock Haven,Pa. on climb out the #4 Jug failed to hold temp. and I could feel the little vibration of the miss firing. I flew for a half hour and it never came back on line until I pulled throttle back for landing. On the ground at idle all temperatures are ok. We are going to pull valve cover on #4 exhaust valve and check for broken valve spring and also move piston down and hammer on valve with rubber mallet to see if it solves my problem.

edasmus · #2 01-04-14, 08:33 AM

Hi Dale,

I am not a mechanic but clearly your cylinder is not firing. I am curious why you suspect a "sticky" valve? It could be that but it could also be something else. Make sure to check ignition leads, maybe swap a fuel injector and see if problem remains unchanged or follows the injector nozzle. Replacing plugs eliminated a bad plug theory but I would make sure to exhaust all other possibilities before pulling the jug. There is probably other trouble shooting items to check, maybe the flow divider. I don't know if it can fail in that manner but I do know you need fuel, air (compression), and spark to have combustion so check anything that has anything to do with any of these.

Good luck,

Ed

edasmus · #3 01-04-14, 08:52 AM

Oh and one other thing, did you look inside the the cylinder with a boriscope (spelling?)? Check the face of the exhaust valve (the smaller one of the two) and look for uneven heat signatures. The face of the exhaust valve should have a very symmetrical appearance sort of like looking at a pizza with the sauce spread evenly over the entire crust. If the valve is not seating properly, the face will appear uneven where the "hot spot" is. If you see this, this is very bad and should be removed immediately.

hharney · #4 01-05-14, 10:27 AM

The scope is a great tool to investigate the issue. I have had valves stick before and ended up with bent push rods and tubes. I would not operate the engine until the symptom is verified. If you can't verify the issue then pull the jug and proceed with overhaul or evaluation at the shop. Check the cam lobes carefully for any damage also if it was a sticky valve.