Was the core plug replaced when you had or BRM rebuilt the engine?
If the core plug is poping before the rad cap opening there is something wrong with the fitting of the core plug. Lots of things will fail before the preasure removes a core plug.
Did you find the old care plug?
@lynx started
London Fixed Gear and Single-Speed is a community of fixed gear and single-speed cyclists.
Was the core plug replaced when you had or BRM rebuilt the engine?
If the core plug is poping before the rad cap opening there is something wrong with the fitting of the core plug. Lots of things will fail before the preasure removes a core plug.
Did you find the old care plug?