Fine reproductions of Knucklehead cylinder heads to replace your worn originals or to build your bespoke custom engine. They perfectly handle larger displacement engines but also work well as a high performance upgrade for 61 cui. and 74 cui. engines. These heads have the late style big port intake flanges, as original for 1940-47. Valve seats are hardened for the use of today’s unleaded fuels and sized for stock 1.750” Ø exhaust and larger 1.940” Ø intake valves, but not machined. They feature stock 18 mm spark plug threads and a stock head bolt pattern, however, the head bolt threads are changed to UNF 7/16”-20 so you can use more common Panhead/Shovelhead head bolts. Valve guides for S&S aluminum valve spring covers are included, but not installed.