Vauxhall 14-40

1926 Vauxhall 14-40 LM Type engine drawing

This shows the engine with the "bath tub" pattern cylinder head which, contrary to popular belief, was used on later models instead of the earlier design of Ricardo combustion chamber cylinder head. The reason is that the engine run more smoothly with the "bath tub" cylinder head, although the performance is not as good.
These cylinder heads were all cast in aluminium, but in very poor material. Also the design is such that there are very large areas of flat metal around the cylinder head joint face, which does not allow the head to seal very well. A further complication is that aluminium, being a very good heat conductor, takes the heat away from the combustion chamber so that with the side valve configuration the flame goes out and this also has a negative effect on performance. It would have been a much better design to have used a cast iron cylinder head.