This DIY was inspired by Taiwanese SYM T2 Club. A experience mechanic found the crankcase breath hole is too compact and the pressure in engine is not release efficiently. It can causes the engine temperature rise up, engine oil leaking and sluggish engine running.
He had no bad experience with the additional crankcase breath hole after running more than 10,000km.
Recently I found my SYM T2 is somewhat hotter near the engine area, however the coolant lamp is not light up (means coolant is good). The feeling of acceleration is ‘hard’ especially above 7000 rpm. Then this photo caught my attention the important of the crankcase breath hole. According to the owner, the engine case was cracked and the oil spills out. Many members was shocked because no one reported such incident yet. The other explanation also could link to the poor material or quality control of the crankcase. It doesn’t make sense to me that engine pressure able to damage the crankcase and blow it apart!
This DIY project is very simple, you will need a power drill machine, paper hole puncher, sand paper and wrench size 10. Please do this while your engine is cold! The crankcase cap is locate at the right side of engine, same side with the engine oil cap. After dismantled the cap, cover the crankcase with a piece of cloth to prevent foreign materials goes into the engine.
After removed the two screws, you will able to remove the diaphragm (a paper card) from the cap. This is to avoid damaging the diaphragm during drilling. Set the screws back and drill a hole opposite the small breath hole. I am using the 5mm drill to make a hole just as the Taiwanese expert did.
Then remove the screws again and polish the drilled surface with sand paper. Match the diaphragm with the new hole position, and use paper puncher to make a breath hole. Clean up, dry off and put everything back. Phew!
The verdict: Smoother engine rev, less ‘stress’ when it approaching high rpm. Engine braking seems weaker now, probably less pressure ‘hold back’ at the engine so beware of your new braking point. Engine sounds a little bit quiet (but who cares). Top speed no change but fun of riding +1 point 🙂