A 2-stroke engine is built and runs differently to a 4-stroke one. A 4-stroke engine keeps most of its oil in its crankcase and oil sump and recirculates this oil to lubricate the engine. With a 2-stroke engine, the process is somewhat different. Here, there is no oil sump as the crankcase deals with the compression and induction of the fuel/air mix. The only way, therefore, to provide oil to the engine for lubrication is by adding it to the fuel. As this oil is burnt with the fuel, it can’t be recirculated. A specific 2-stroke oil is needed as 4-stroke oil would leave damaging deposits behind when it burns.