Does anyone know where I can get cam gears that are made of metal? I've gone through two cam gears. The first was completely disintegrated into many pieces. The second has a hole wearing through on the cam lobe. I don't know what is causing the problem. Also I have been having problems with exhaust valves dropping. The first valve dropped on the first 142F engine with no damage to the cam gear. Both the damaged cam gears came from the second 142F engine which also dropped an exhaust valve. I did what was instructed fom Bicycle-Engines.com with the second engine, using low grade fuel and a colder spark plug. But it still dropped the valve and I don't know why. Also would full synthetic oil have anything to do with the deterioration of the plastic cam gear?