warrior2

I have a new FS26S. I installed it inverted in a .020 Cub. It ran OK for a while, then I throttled it down. As it came to idle, it began to run rich and quit. I cranked it back up and it did the same thing again. When I cranked it back up this time, it made a loud clicking/knocking noise, but cranked up and the knocking quit. Afterwards, in checking the play in crank, it had several places where there would be a noticeable knock. I removed the backplate to examine the con rod. The problem (and knocking noise) is that the piston moves up and down about 1/32" freely and makes the knocking sound at the ends of this travel. The con rod seems to be OK. I have not removed the piston yet. Could this be a broken piston or broken ring? Should I not run the engine inverted due to fuel accumulation in the cylinder?
Thanks for any tips.

Bax

My Feedback: (11)

If you remove the glow plug, and the engine turns over smoothly, then there's nothing blocking the piston. If you hear "clinking" sounds, that's normal when turning the engine over by hand. It's just the valve train working.

If you hear a clatter when the engine's running, it could be a result of an overheat, and you're hearing some piston slap at low throttle settings...you'd have to do a full teardown to check.

Your problems with inverted running are typical. You may have to lower the fuel tank a bit, add on-board glow heat at low throttle, or just accept a somewhat higher idle. Any of those could cure the difficulty.

warrior2

Thanks. After further inspection, nothing seems to be mechanically wrong with the engine. I'll try mounting the engine horizontally and see how that works. Also, how many tanks of gas (6oz) at rich setting should be required for break-in on this engine?

Thanks again!