You can do like I did,take a old glowplug.Hammer a flat end on it.Grind it to where it sharp,but only .030 oversize standard glowplug.Gently screw it in,you may have to force it, to break carbon.And unscrew,then turn engine over a couple of times to blow out carbon.Remmember size of your reamer should not be as large as threads.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt