When I try to start my bolens bl100 the motor will not engage what should I do to fix it.

Hi,
I gather that you are saying that there is no engagement between the starter pulley and the flywheel. This is usually indicative of stuck or damaged pawls on the flywheel ar a damaged pulley. Link will give you the manual(in 3 languages) and has a parts breakdown in the back. Page E21 or 61 is the engine.
http://dl.owneriq.net/5/5cb63bf0-5bde-4d81-9e9a-79ef11fba4b2.pdf
Peace,
Clarke