Two years ago someone gave me this engine. After starting it up I realized it had bad rings. I took it apart intending to replace them but the engine ended up a basket case. As he was building a go-kart I had my little brother put it back together. He did a good job except for one thing. A very long spark plug somehow made it into the mix. So long in fact that upon starting the engine the plug made contact with the intake valve, which through off the valve timing causing it to blow gas out of the carb and suck air in through the exhaust. I know some smaller engines have a plastic timing gear that strips instead of the more expensive metal ones. Does anyone know the timing layout of this type of engine? It's a 20 HP twin cylinder from an MTD rider. The model number is 460777.