I was wondering i have a 2.5 traxxas rustler and the other day i opened up the cooling head and i saw that the top of my piston was black.Now does this mean i should get a new engine or what please help.

Hey,does it run o.k.? or whats wrong with it?other than the black piston.

well it overheats but i think it justs needs a little tuning i called the hobby shop yesterday and they said when the fuels and oils and everything burn it will leave the piston black so i guess thats it

What your seeing is castor buildup on top of the piston, most fuels have some castor so it does not matter what fuel you are using.

It does not mean your engine is toast, actually castor buildup is good in a 2-stoke. Castor buildup actually helps build compression.


Dbow

yah sometimes buildup is good because it means there is less cc's when the piston hits top dead center and that means more compression and more compression equals more power. Besides, no fuel burns clean except for pure methanol. Some people at the go-kart track i race at got d'qued because they had a carbon buildup and there weren't enough cc's in the cylinder.

Ya I had that happen once I sure hope it does not happen again it cost 50$ to repair I blew the piston rod and sleve and everything it was a mess the coss of it it was running to lean.

Wow, bad experience I guess, I have never heard of castor build up blowing an engine.
Castor deposits are very gooey and will wipe right off in most cases with some WD40 or cleaner of your choice.

If someone has an excess of buildup then something is wrong, the engine could be very rich , in wich case you would foul plugs one after the other.

A good used glow plug can tell a lot about an engine, there should be a slight brownish color on the bottom.
If the engine is tuned properly you should see several gallons of fuel on one plug. I get about 2 gallons on my MT's and about 2 gallons on my plane engines, I usually change them in my planes at about 2 gallons even if they are still running good.

Dbow