COMP Cams Tools 5639 COMP Cams Adjustable Valve Spring Tester checks spring pressure on an assembled engines. This billet aluminum tool fits onto your rocker arm for quick pressure checks. It is adjustable for use with almost any rocker length and measures pressures up to 600 pounds. Adjustable On-Head Valve Spring Pressure Tester COMP Cams Adjustable Valve Spring Tester COMP Cams Gauge Adj. Valve Spring Press