I use these hook-shaped tappet-holding tools (see photos) for adjusting the valve lash on my 1952 8N flat motor.

Made from 3/16” steel rod, the end of the hook (1/4” long) fits into one of the four tappet holes. The horizontal top of the hook (7/8” long from center to center of each arm) has a slight horizontal bend half way along its length; this allows slightly more clearance for the adjusting wrench. The long vertical part of the hook (not more than ¾” long) anchors in the valley between the block’s tappet bosses, stopping tappet rotation when using the adjusting wrench. I bent the rod in a 6” vice, using a hammer to make compact bends (especially for the 90o bend that makes the ¼” hook).

The right-hand version stops tappet rotation when decreasing lash; the left-hand version stops tappet rotation when increasing lash. The tappet-holding tools shown here have handles 2 ½” long and work on all valves, although short-handle versions have more clearance around the governor linkages when adjusting #1 exhaust.

I made the adjusting wrench as described in both the IT FO-4 Manual and the Ford 8N Operator’s Manual. The 4-hole design of the tappets combined with the 6-sided adjusting bolt results in various alignments between the tappet-holding tool and the adjusting wrench that allows adjusting bolt rotation at specific locked positions.