Haven't seen any on the web, but here's an alternative. Contact Briggs & Stratton. Tell them that you are working on a project that involves placing one of thier engines in your product and that you need a 3D model for space constraints and mounting purposes. If companies use 3D solid modeling, they usually are pretty good about getting you what you need. It might be an unintelligent file though, like IGES or STEP.