Q: I have a Nitro Burner (8471) but the pull-back motor has a different shape than shown in the building instruction. What should I do?
A: Simply keep building! The new shape of the motor does not affect your Racer. As you can see on page 25 or 43, you can add black TECHNIC beams to either side of the motor and these can be used to build up the Racer.

Source: http://web.archive.org/web/20061210085834/http://www.lego.com/eng/service/faqs.asp?section=ConsumerService-FAQ-Products&catid=68E505FF-CB53-4309-810B-F90ACA36BB96&faqid=1564#1564