Stuck Exhaust Valve on O-200 – Lessons Learned & Preventative Maintenance

[TOTE]

A few months back, I had a pretty eye-opening engine issue in my 1967 Cessna 150 (O-200A). While transiting over Ontario (KONT) at 2,400 feet, I started experiencing severe engine vibration. I initially thought it could be carb ice or a fouled plug, but after troubleshooting with mixture, throttle, and carb heat, it was clear something was mechanically wrong. I had partial power, but not enough to maintain altitude indefinitely. Given my position, I declared an emergency and landed safely at Ontario.

After getting the aircraft to an A&P friend of mine, we found the culprit—a stuck exhaust valve. Ironically, I had planned to clean the valves and guides that very week, but the engine decided it couldn’t wait. We pulled and cleaned the stuck valve two days after the event, and I was able to fly the aircraft home. Since then, we’ve reamed all the exhaust valve guides and updated my valve cleaning interval from 300 to 200 hours to hopefully prevent a repeat event.

I know the O-200 is no stranger to stuck exhaust valves, especially with the way it manages heat. For those who have dealt with this issue before, what has worked best for you in preventing recurrence? Have you had success with a more aggressive cleaning schedule, different oil/additives, or other preventative maintenance techniques?

Would love to hear from others with O-200 experience—what’s your go-to method for keeping your valves happy?

 

[Magman]

When 150’s were new sticking valves were not a common event. But that

was on 89/87 fuel. 100LL did not play nice with O-200’s. If I had another

150 my thoughts would be using Mo-gas more and a oil filter/ shorter oil

change interval.

 

[Rcmutz]

Aggressive leaning on the ground. Can’t hurt the engine at the low rpm setting used in ground and taxi ops. I’ve done this on my O360 in my Tiger for years. I also run REM37BY plugs which are hotter burning. For the O200 I’m not sure if there is an alternate hotter running plug.

 

[Dan Thomas]

Don't leave the valve guides at the minimum bore diameter. It takes very little carbon to seize the valve with minimum clearance.




As much as .008" loose is OK.

 

[ateamer]

Several A&P IAs recommended that I either run mogas if authorized, or add TCP, a lead scavenger, to the fuel. It helps to keep lead in suspension and exit through the exhaust system instead of sticking to the valves. TCP isn’t cheap, but I’ll use it because access to non-ethanol mogas is harder than getting 100LL in our situation.

Remember that 100LL is low lead compared to the 100/130 it replaced. It has four or five times the lead that 80/87 had.

 

[texasclouds]

My friend’s 150 aerobat was sticking valves until she switched to 87 ethanol free from walmart. No more issues.

The flight school 150m never gave us problems on 100LL, so ymmv.