Starter, weird situation

[Subiequad]

So I was trying to replace the starter on my 87 warrior, the housing that extends out on the old starter has sheered off into the block, so I went to Take the outer casing off, now my quad has a pull starter (with does not work also) but the case will not come off due to a bolt that is on the pull starter wheel (anytime I try to tien the bolt the motor turns over), are there any tips or ticks that might possibly help me to get the case off, or get that housing off with out damaging the engine Or the pull start which I intend to fix for this scenario, or should I take it to a shop