Well I don't have an excat mileage on the Engine overhaul but the Chassis Repair can be done if you slam into about 2-3 walls full speed. Or if you hit walls alot maybe inb a couple of races --- "Ignorance and stupidity will be the downfall of society"
Is there a way to tell if your chassis needs to be overhauled? Like is there a meter or something? I've also heard the chassis overhaul is based on milage like the engine and it doesnt matter if you crash or not. I'm not sure though.