Ive always raced electrics and now Im venturing into the world of nitro and have a simple question. On my 2.5 I took the head and glowplug off and noticed that the piston had a black spot on the middle of it. Is that normal and what is that caused by.

Have noticed anything strange with your engine? does it feel like your engine is loosing power? is your engine overheating? i recommend you get a temp gauge and check the temperature on your engine. it might be overheating and destroying your engine.

the piston will get dark/black after use. nothing to worry about. it runs fine, right? the black comes from the burning of the fuel. no worry.

Just make sure you dont have any pitting on the top of the piston.

Any views about the STS 21 engine??

Joe F

Unless there is noticeable running problems I wouldnt be worrying to much, you got a picture of it??

get a temp gauge anyway. the same thing happened to me with the HPI 15fe that came with my rs4 3. i thought it was just normal but eventually my engine was destroyed. i think i had it way too lean. w/e cause i upgraded to the T-15....... great engine.

have u removed headshims from the engine? make sure there is atleast 1 head shim between the head and the sleeve because the glowplug may be abit too close to the piston or u dont have a the brass washer on ur glowplug....come to think of it my navorossi .12 has got a totaly black piston the top of the piston is black like a permanent marker...i got the engine 2nd hand and its not pullstart so i cant realy start it up