I think it is best to completely dissasemble the engine en clean every part thoroughly. If you don't know how to do that, search on google or [link=http://www.hpieurope.com/walkthroughs/rebuild-eng/engrebuild.htm]look here[/link]. You must understand that even the smalles dirt particle inside your engine will ruin it in less than a minute (if it's not already ruined). And while you are at it, you can check if the piston/sleeve needs replacing or not.