Thankyou drivewithken,
I have managed to installed the belt purely by guess work, the machine is stitching, but now and then it breaks the needle. I guess my timing must be close but lacking in precision. If you can kindly help with instructions, I will not have any problem. You are right, the top shaft is the drive shaft that drives two bottom shafts via timing belts. I removed the belt towards the stitching side. I have never in my life repaired a sewing machine, but I have years of experience in machanical engineering.
Riaz Ahmad, June 2009