Yes, financing a motorbike can help to build your credit. As long as you make your monthly repayments on time and in full, over a long period of time you may see your credit score increase, which may help you obtain credit in the future.
You might notice a slight drop in your credit score when you first take out motorbike finance. This is because you are opening a new line of credit, and the lender will make a hard credit check. Both of these things affect your credit score.
Repaying your bad credit motorbike finance will only help build your credit score if you are repaying all of your other debts on time. If you have other lines of credit, and make repayments for those in full and on time, it helps to build your credit history and shows future lenders that you can manage credit responsibly.