Yet the same engine fitted in the earlier FH series was pretty reliable, due mostly to having a vertical radiator which gave a good head of water above the cylinder head. A nightmare to work on though, removing the nearside wheel to get at the rocker cover and then having to remove every stud from the cylinder head before you could squeeze it out between the cab base and the chassis rail! And dont even mention the three piece sump! 
We serviced a ‘chinese six’ FH coal tipper which had a Primrose second axle, the master cylinder was seperate to the second axle and was always going out of adjustment so the brakes wouldn’t work but engine wise it had no real problems. It gave aid during the Aberfan disaster as it collected coal from those pits back to the yard in Reading.
Pete.