That tell tale puff of blue smoke when you first start is an indicator of worn guides or seals.
Valve guides should be replaced with every valve job.
These are the original quality Cooper S guides for use in any head that is leaded petrol or uses chrome stemmed valves.
Also suitable for any of our plasma or heat treated competition valves when using unleaded petrol.
Not for Turbo exhaust valves as they have a 8mm internal diameter.
Recommend: 8 x 12G1963 per Mini.
For valve stem top hat seals, see ADU4905