what are your thoughts on the following dilemma.

a website for a car mechanic is to expand its product line, they want to keep the same website but to extend it to sell 2 other lines that are barely related.

he wants to sell custom made carbs and also to have a website for car restoration, old fords mainly.

he dose not want three sites or even two but to keep everything on the same site, i know i can just add a new index pages - repaircars/carbs and repaircars/restoration which is easy enough but after visiting the H&M (clothing retailer) site he has asked for a front page that has only 3 links, one to his existing car repair workshop, one to the custom carbs and one to the restoration side of the business, all three businesses will come under the same business name so no problems there but i wondered if he would lose his pagerank of 4 as the front page of the site will not be the existing page but be this new portal type page, if its a good idea (it does make sense) or if it will actually cause him dearly in the search engines as there is no point in hurting his existing website of 4 years. ???????????

any thoughts appreciated.