I remember reading some history of the Coventry Climax engines a long time ago. The design was as a fire brigade water pump engine which had to be light enough to be carried in a cradle, and capable of being started and run at maximum rpm from cold. So the design was quite loosely put together, such as the fit of the pistons in the bores, which caused oil consumption - not important on a fire pump engine. I guess that the oil pressure relief system was also designed with that in mind.
