This shows the two cams and blade surfaces that wear out. These are off a HC150 but same on SHC212. This the cam and blade interface. When the mating surfaces get wear they will hop up and down and shake and it makes the hedge trimmer difficult to use. This is how you lube these up....at least yearly. Don't use gun grease this it the echo gear case lube. You can get two new cams and two blades for around $110. Seldom does the engines go on these.