The International Cessna^® 170 Association

While climbing out of Oakland the other day my C-145-2 stuttered - just so slightly, but enough to get my attention. The engine has 400 hrs. on a rebuild and I try to fly it at least one hour each week. However, often the flights are relatively short. I use TCP about every other fill-up and alternate with MMO. The stutter felt to me like a valve trying to stick. I'll keep my fingers crossed.

Any chance of some water in your fuel? That is what it sounds like to me.
I've had a couple cylinders with sticky valves last year, but the problem would happen when engine was cold. Once warmed up the shudder would stop. Problem solved with 6 new mellenium cylinders (ouch)!
Cheers Eric

Robert,

The guys down in the big hangar tell me that MMO and TCP cancel each other out.

PS,
I was using TCP almost every tank, and still had a couple sticky valves. I also lean the engine 50 degrees rich of peak at all times (accept during low level climb). I'm not really sure TCP helps based on my experience.
If anything perhaps we should lean 50 lean of peak to help scavenge the lead deposits caused by the high lead levels in 100LL. In a perfect world I would still be using 80/87 as my cylinders were always deposit free.

What an amazing coincidence! Mogas (Auto Fuel) happens to be 87 octane too and doesn't leave any deposits either.

blueldr wrote:What an amazing coincidence! Mogas (Auto Fuel) happens to be 87 octane too and doesn't leave any deposits either.

Yes. And it has alcohol to boot!

Stuck valves are not always caused by lead, and the use of TCP certainly helps keep the lead deposits down. MMO also has a reputation for keeping valves well-free. So,... perhaps you have another cause for stuck valves (if indeed you have stuck valves, which have not yet been proven to be the problem.)

Stuck valves are frequently caused by oil which has overheated and "coked" onto valve stems. This can be caused by hot shut-downs, incorrect oil viscosity, poor cooling due to baffle condition, and sometimes operator error (long climbs at low airspeeds/high power settings in high ambient temps), and frequent power changes such as flight training ops. The C-145/O-300 Operator's Manual, Form X-30016 advises on these things, and suggests allowing the engine to idle at 800 RPM until cylinder temps have been reduced before shut-down. I personally believe that hot shut-downs have contributed to stuck valves (Continental "morning sickness") on start up.

A "stutter" on climbout is not necessarily a stuck valve. Stuck valves are VERY rough!...you'll think it's about to quit!.... not just a "stutter" (which I guess is a term we should better define.) A short "miss" that goes away is usually poor fuel quality or water or carb ice, or a malfunctioning magneto or ignition anomaly. (Bad ignition lead, failing condenser, carbon-brush or carbon arcing or contamination inside the mag distributor, etc.) A stuck valve is a VERY rough engine due to a cylinder which is virtually DEAD during the event. Once you've experienced a stuck valve, you'll KNOW what a stuck valve is like. I've made a precautionary landing because it was so rough. (Not on my airplane, thank goodness! But on another Continental, with the same cylinders, ...an O-200 on pipeline patrol.)

My engine gave me an occasional "stutter" on the way to the Las Vegas convention, which was discovered to be a leaking oil-seal in the magneto. Changed the seal and cleaned the magnetos internally and no more "stutter".

Having had a stuck valve I can attest that it is a shutter not a stutter. My engine ran so rough you knew something was drastically wrong.

Robert Eilers wrote:While climbing out of Oakland the other day my C-145-2 stuttered - just so slightly...

My C-145-2 does that a few times a year also and it happened just the other day. A mechanic said it's probably ingesting carb ice and I have to agree with him as I can duplicate the same stutter when in fact I am building carb ice and then apply carb heat. It makes sense here this time of year where temperatures are dropping and humidity is high.