How to Perform a Professional Valve Job  Dotted lines or skip marks on valve faces after lapping-in means the stone in the valve grinding machine needs to be trued-up. The stone must be periodically trued-up, because due to a lot of use, it will wear unevenly, resulting in erratic or unsmooth valve face grinding. TENDTOOL- Valve seat inserts in Kohler flathead engines, with the exception of the K361 OHV engine, are made of extremely hardened steel and rarely wear, get damaged, crack or loosen. In fact, I have never replaced a valve seat in any of the 100’s of Kohler flathead engines that I’ve professionally rebuilt over the years. All I do to valve seats is recut or regrind the 46º [intake or exhaust factory angle] or 31º angle [intake only; to increase airflow] to put them […]