[Healeys] BN1 Radiator cap

[STEPHEN CUSS]

Hi,
 
Can someone help me find out what model of radiator cap should fit a
standard 100/4 radiator. The cap I have doeas not seem to push the spring down
as you would normally expect, Should the cap be long reach? Also what is the
pressure in Lbs before the spring gives as I know not all caps are the same.
 
Thanks in advance for any help with this matter.