i agree with the previous posts buy another engine....
is this the Mach .15 with the black head or the blue one
if it is the blue one don't waste ne money on a head being how the engine wont last long anyways (past experience)
if it is the black one i heard that it last a little bit longer that the previous model
but still don't buy a head for a rtr engine
invest in a good engine like stated in the other post (fantom, o.s,Novarossi, rb,picco......)