The valves that come with the engine are some of the poorest quality valves I have ever seen. We are replacing the isolation valves with the Bray valves which have a wafer thickness that matches the DIN dimension of the OEM valves. This makes the swap out an easy project. The Bray valves seat well and will stay in the position that you need and not float because of vibration. The cost of the valves is very reasonable 4″, DIN 100 is $150.00. We have 4″ through 8″ valves as replacements.