Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > General Motorcycles only > Ports

[custard]

I have a Yamaha sr500 cafe racer, that I have just stripped ready to rebuild.
As I have the cylinder head off is there any benifit to having the ports polished? I used to have a two stroke and that improved it having them done, so is it the same for a four stroke?
anyone

Rich

[rockhopper]

Its generally thought that polishing the ports on a four stroke motor is a bad thing. A rough surface helps the fuel/ air mixture to stay together ie it encourages turbulance. A very smooth surface can actually cause the fuel to drop out of suspension.

[skidlids]

You can improve the porting by cleaning up the original cast finish, removing any flashing marks etc, also look at matching the port inlet to the inlet rubber. Smoothing out the port surface helps but as mentioned a void the polished finish, port walls that feel smooth to the touch are what you want as at a magnified level they would still appear rough and allow a layer of fuel molecules to cling to the wall to improve flow.