A little bit of reading in this forum would give you the answers. Also you don't tell us your status in Singapore, which does make a difference.
But as I am nice, then you need to know the following:
1) You can ride any size motorbike on your foreign license for UP TO ONE YEAR. You MUST convert within a year of arrival.
2) If you are on a STSVP you may drive for up to 12 months every time you enter Singapore.
3) IF you become SPR or SG Citizen, you must convert immediately. (if you previously held a SG 5-yr licence, you must convert to lifetime licence when you become PR).
If you need to convert your MC licence, you have to take a Basic Theory Test. This will guarantee a class 2b (<200cc) licence. From the Traffic Police Website:
"Conversion for a higher capacity or open category motorcycle licence is normally not granted unless there are documentary proof of training, testing, ownership of bigger motorcycle and insurance policy indicating that you have gone through proper training and testing regime and have had at least one year riding experience on the road."
Some of us older folks with lots of documented experience on big bikes have a full Class 2 licence conversion no problem. Other people not so lucky.
Full details on the TP website:
http://driving-in-singapore.spf.gov.sg/ ... ersion.htm