Eagle One Etching Mag Cleaner is some great stuff!!! Have you ever tried to clean your engine? Yeah, nothing seems to work huh, The dirt is baked on!! Clean the loose dirt off the cases and spray this stuff on. Let it sit for 3-5 minutes and whip it off with a rag. I used an old tooth brush to get in the tight spots. Be sure not to leave it on there too long though. I did it wilthe cases split and all tore down. I'm sure you could do it with the engine still in the bike. If you are going to do that, spray it on, let it sit and then use a water hose to rinse it off. This stuff will eat paint off lol. Here's a pic to see how well it does...