Use a piece of copper tubing with a flat end and filed to a edge or alloy will do, scrape slowly and gently do not gouge the soft alloy cover,then gently rub with p240 wet&dry to finish ,do not get grit in engine so clean often a vacuum cleaner works well here,allso try putting the cover on a quality piece of glass to check for warpage of the cover ,try to slip a piece of paper around the edge .
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Use a piece of copper tubing with a flat end and filed to a edge or alloy will do, scrape slowly and gently do not gouge the soft alloy cover,then gently rub with p240 wet&dry to finish ,do not get grit in engine so clean often a vacuum cleaner works well here,allso try putting the cover on a quality piece of glass to check for warpage of the cover ,try to slip a piece of paper around the edge .