Hi, regarding the chain, check the tension and alignment if all ok then check the chain for a dry tight link. If nothing found check the condition of sprockets. Regarding the overflow from the cooling system, first check the coolant level from cold, then run up the motor check to see if the thermostat opens and then continue and make sure that the fan cuts in at the correct temperature. if all this is ok l would then suspect that you've got a weak radiator cap. When the motor is stopped after a run the water pump also stops, this causes the water in the hot engine to pool up and boil, this hot water should be accommodated in the expansion bottle. If the - radiator cap is weak it will let go of the water and release it out of the overflow pipe which is what your seeing. Hope this helps