I have had my RCS180 for a couple of years. At the end of last year, it was running poorly. This year, I could not start it so I looked at the carb and found a lot of junk in the screen. I cleaned the screen and the engine ran like a top. It is starting easily and turning a Mejlic 20x6 prop at 8,000rpm.

Today I was flying at half throttle and the engine just quit. It turns over freely, but it lacks compression and will not fire. I took off the backplate and everything looks clean. I cannot tell if the ring is stuck, but the piston and sleeve does not look damaged. The plate, on the back of the drum, has a hole that fits over a pin sticking out of the crank pin. The hole in the plate is elongated, top to botom. Is that normal?

Can anyone suggest what I can do further evaluate this problem?

Stuck piston ring? Or loose head or jug? Spark plug threads going? Or is spark plug tight? The threads in the head of the spark plug can strip really easily. Also try a new plug.

Gunny

I have since pulled the head and the jug. The sleeve and piston are scored on two sides. There is no debris in the crankcase. It appears to be from a lean run, although, the engine was running rich at the time. I was using the last of my one gallon can of gas. Could it be that the oil content was low? I use 87 octane and 50:1 Klotz. The engine is two years old and has been urn extensively. When I cleaned the screen in the carb and switched from a 20x8 Menz to a 20x6 Mejlic, the rpm went up to 8,000. I wonder if this is too much rpm? I was advised, by users of this engine, that they were running Mejlic 20x6 on profile 3D planes.

Chances are the engine was running on the lean side due to the crud in the screen. It also could just have been "its time to go"... the engine might have been running lean before its demise and when you cleaned the crap out of the carb screen now running at top RPM and mixture - it lets loose. Sounds like you have a lot of flights on it. Those engines are quite picky mixture-wise.. They run hot as it is, so a lean mixture will spell early death.

I have never run this engine above 7500 RPM. I used an 18x8 prop on my RCS 180.. After about 50 flights, the front bearing siezed and so that was my first and last RCS engine-- nearly lost my CAP on a dead stick. I switched over to a 3W-24 , not a problem since and 100+ flights...

The RCS was a nice engine before the problems though...

DP

You say it was the last of a gallon of fuel. Was it old fuel? That can cause carb and engine problems, the oil will also settle to the bottom of the can. I've found 91 octane to have a longer shelf life. It's a good idea to shake the fuel can to get the oil mixed in. If the gas gets stinky, don't use it.

I ran into a guy today who has been into R/C boat engines for many years. I have not seen him since the '80s, but he is a good engine man. He told me that part of my problems were due to using Klotz Two Stroke oil. I usually pick up several quarts of Klotz, at the Toledo show every year. I have never had a oroblem before. I mixed this up a few weeks ago. I have a 3W60k and use the same gas. I bought some Amsoil as many Giant scalers use that.

I have used Klotz for years.. never a problem.. I have seen problems with Amsoil however...

DP

I was using Klotz Technoplate. RCS suggested that this was not the best Klotz oil for this engine. He did suggest High Qual HR1 or something similiar. He also suggested that I go to 40:1 for break-in again.

I had the sleeve honed and had a new ring put in. The engine runs at 8K with a 20x6 Mejlic, but I am using a Zinger Pro 20x8 at 6700rpm. I can fly the 106" Citabria at half throttle with just enough grouind clearence and can probably all floats later.