Is There any way to convert400 crank form external balanced to Internal balanced?

 

No but they sell 400 cranks that internally balanced. The only thing you need to do to balacne it is balance the flywheel.

 

sure get it balanced for internal and run neutral or internal balancedampner and flywheel. might take a bit of mallory metal but it could be done. depending on the pistons and rods you run the weights could be built up too. i think all in all you'd be ahead to buy another crank already set up for internal balance.