They subsequently fell from use due to advances in poppet - valve technology , including sodium cooling .
The Knight system double sleeve engine 's tendency to burn a lot of lubricating oil or to seize due to lack of it .
They subsequently fell from use due to advances in poppet - valve technology , including sodium cooling , and the Knight system double sleeve engine 's tendency to burn a lot of lubricating oil or to seize due to lack of it .