ORIGINAL: nitrorcjunkie
ORIGINAL: acexxxoasis
well the sleeve AND piston expand and when the sleeve expands onto the expanding piston your adding pinch to something that requires certain tolerances to keep compression, also when running hot your usually overly lean and your engine isnt getting the proper lubricant so things heat up more and wear MUCH faster also your connecting rod heats faster trying to pull heat from the piston so it heats up and you can over stress the connecting rod you can stretch the bushings. this is after a long time running like this. short periods wont kill your engine but youve got a track record with engines
When the sleeve heats up and starts to expand, it grows in outer circumference, the diameter of the inside of the bore will increase, not pinch down around the piston. This is due to the fact that, on a molecular level, metal expands in all directions equally- picture the individual molecules of metal as balloons being inflated. Since the cross section of the sleeve is say, .125" and the circumference is around 1.25" the increase in circumference is 10 times the increase in wall thickness. Look at it this way- if you have a metal rod with a diameter of .125" and 1.25" long, when heated, the length would increase more than the diameter would. So, when you overheat the motor, the sleeve will not squeeze tighter on the piston due to the sleeve expanding, however the piston is also expanding and increasing friction between piston and sleeve. This excessive wear ruins the pinch, wearing out the motor. High engine temps destroy the lubricity of the oil, wearing out rod bushings and bearings that are designed to be constantly lubricated. How's that for some science content?[8D]
is that why it is hard to start a rc motor when it is hot/overheated?