Of our 4 “A” series 18V50SG units, we have experienced two cracked cylinder heads. Each time the head cracked in the same place, in the intake valve tenon between the valves. This allowed cooling water to leak into the combustion chamber, causing the affected cylinder to misfire on the first start attempt of the day, followed by a normal start on the second attempt. This is not repairable per Wartsila, and the head must be scrapped. The first occurred at 5564 hours, the second at 5345 hours. These are peaking units, averaging 10-12 hours per start and are operated at 100% load.
Is this a common failure on the 18V50SG? And is the “B” series cylinder head more reliable or less prone to cracking?