How can I clean spark plug chamber with head on?
Don’t go overboard! All they are wanting you to do is to clean out the threads! A vaccuum cleaner would be nice to remove stuff in hole around sparkplug, so it is clean there! If the threads are full of grit and possibly sand, screwing the plugs in will cause a little damage to threads, and done often enough it will make threads too weak to hold plugs in tight! You can buy a sparkplug “thread chaser” and screw it down in threads to clean out and lubricate threads (with a little WD-40 if you like). All the small particles etc. that fall down in cylinder will blow out the exhaust when the engine starts! Though I haven’t used one in years, — I just run plug in and out a couple times with light oil on threads to make sure the threads are clear of chips, — this is done with my fingers, — (not a wrench), — so I can feel if there is a problem, and check to see what it is! If really messy, I blow out as much as possible with compressed air before removing plugs!
