ORIGINAL: freakingfast
Exactly, I’m convinced that I can’t just run it out of fuel and use after run oil to get rid of the nitro. I found that if I don't flush it with FAI fuel, a few days later there is a very subtle gritty feel to the bearings. I’m thinking that these are little rust spots on the balls and races from acids formed by leftover nitro residues.
Correct,
the oxidative nature of nitro fuel to most metal surfaces (ferreous, aluminium, brass) should not be undervalued.
For instance there are R/C speed boat classes using > 50% nitro fuels. These engines have to be “cleaned“ internally with straight FAI fuel (80/20) after each race.
Procedure:
Most important is that the engine has to be “afterrun“ with the zero % nitro fuel
at hot operating temperature. The high internal engine housing/cylinder/bearing/crank etc temperature together with
pinching-off the fuel delivery at full throttle ensures complete evaporation of all nitro and methanol residuals within the engine.
After that zero nitro afterrun procedure only the lube oil is left within the engine being a perfect conservation until next week’s operation.
Additional special afterrun-oils are not necessary as a rule.