07 crf 250r, tore top end down, new piston, cylinder and valves, while replacing head I noticed the post on the left side intake appeared to have more threads exposed. measued, and in fact it does. With the washer on and I tighten it down it will push thru the top of the acorn nut, What would cause this? Could the post have pulled up? Can I put an additional washer on to take up thread?