11-08-2017, 01:53 AM
(10-08-2017, 07:36 PM)seajayare Wrote: My new to me "special" ( Cambridge finned head, 2x SU H? carbs) came with NGK B6HS plugs. Looking at the old forum people were using NGK BP5ES plugs successfully. As I think a couple of my plugs were dodgy I bought 4 new BP5ES (less than £6 delivered for the 4) which arrived today. The reach is about 20mm compared to the current ones about. 13mm. Are these new plugs going to be ok do you think?
You probably need a BP5HS, the P is for projected nose, the 5 is the heat range and HS denotes short reach, the plugs you have purchased are ES which as you have discovered are long reach. There are two problems with these in a head with a 13mm thread length, firstly they will stick into the combustion chamber much to far and quite probably hit a valve. Secondly even if they do clear and the car will run, carbon will build up on the exposed thread which can lead to preignition, and worse when you try to remove the plugs later could jam and cause the soft aluminium thread to tear out.
Black Art Enthusiast