hi

I have a 46 fx that i run on Byron Fuel. 5% nitro, 16% synthetic/castor. I dissassembled the engine and found pitting on the cylinder head. Hmm that means detonation or pre ignition. Detonation would have been due to a lean run right? so i can prevent that by being more careful with needle. Pre ignition is caused by hot glowing particles igniting mixture, in full size aviation it is usually chunks of carbon. None of the engine or exhaust is carbon-y so what is causing what I think is pre ignition? Also, should I add more oil to my fuel?

thanks guys

Sometimes, preignition is caused by the compression ratio being too high.

A hot glow plug can cause it too.

A lean mixture sometimes.

A engine that isn't cooling well because of the cowling or being used in a pusher fashion.

Sometimes, the little particles are coorosion from the lower end.

Enjoy,

Jim

Yes, definitely add more oil and play it safe by adding castor. I'd go for 20% total but remember you'll have to retune both the high and low speed needles.

Even a badly carboned up engine never seems to actually preignite. With only 5% nitro I doubt the fuel is causing any problem even if you're using a very hot plug (assuming you're not tuning for absolute peak revs). However, I've seen a 46FX that blew a bearing and that caused lots of pitting on the head and the piston crown. It wasn't very smooth to turn either