As with most of your posts, you need to provide us with more context. Have you changed the belt? Clearly the belt or cover isn't installed correctly. The answer is probably as simple as 'fit the belt correctly' or 'fit the covers correctly'. Is it the right belt? Is the belt trying to 'walk off' the pulleys? If so, you probably have a pulley or idler misaligned.
Is this the engine that you changed from Lucas to Bosch injection pump?