COMP Cams 4900 Magnetic Deck Checker - Professional Valve Spring Height Measurement Tool for Engine Builders - Perfect for Automotive Repair & Performance Engine Assembly

To calculate true compression ratio it's necessary to measure the distance between the deck surface of the block and the piston deck. The machine aluminum deck checker incorporates magnets to hold itself firmly to the block for simple and accurate measurements. Mount a dial indicator in the center for deck height or in each end to check piston rock.