In regards to coments of castor synthetic in nitro fuel blend/contents. It does leave a residue on sleeve liner and piston surfaces ,that will of course vary the many blend out there. My observations are with the 100 plus piston and sleeve sets received here each month for reconditioning-resizing services. Of course this residue (to an extent) is the necessary protection, but will also be misleading (when engine cold) the piston + sleeve sealing capabilities effecting engine compression (power) when at operating temp. From the racers end he will see this power loss (especially coming out of corners) and also very noticable change in ideling capabilities. From my end , the removal of this film/residue is essential so as I can reform/restructure sleeve bore + piston (an accurate new designed fit) to suite a nicely "matched" piston and sleeve set. its intriguing when I first pull a piston + sleeve set out of package for inspection and prep as to how normal felt seal with residue still adhered to surfaces, becomes nil / unexceptionable fallowing first clean up. It veries, I see many sets after just a few gallons from onroasd guys( I used to race onroad myself now race offroad) while the offroaders will go (in my opinion with observations) will run much longer before freshining up the seal for optimum performance. Again , as was mentioned a previous post here, it depends on an engines application and racer needs. Bottom line , with the cost of all these little 2cycle nitro engines we want to get the best engine life possible/available to us. Preventative maintenance with a high level care is essential these high maintenance engines. The other alternative is getting caught up in the engine hype and purchasing new engine more often. I personaly can be concidered more compulsive with bearing changes than resizing my own engines. RayAracing