I'm reassembling my 233 HP Merc(351) IB after doing a valve job and the manual mentions checking valve clearance. The individual rocker arms are not adjustable--it appears that you just tighten the nuts until tight(25 ftlbs?) as they are free spining. The lifters are hydraulic. I was going to bring each cylinder up to TDC and then tighten the nuts but I've heard that you don't have to do that--just tighten the nuts and go boating.<br />Comments<br />Lakeguy72