To explain the problem bit more. I brought a kit from BHT Diffusion and discovered that the chain supplied by them with the kit is small. Hence I had no option but to replace it.
The chain supplied by them is TJC Link chain 1\2" × 1\8" with pin length of ' 8.7 mm '.
The closest to it i can find is bmx single speed Chain
Specification is 1/2" x 1/8" with pin length 10.7 mm
Please can someone advice what is Pin length and that different pin length makes any difference.