Exhaust Valve, Cooper S Mark 1

Exhaust Valve, 30.97 mm diameter (1.22″ (31mm) x 3.52″)

As it is possible, even common, to swap one head for another on 1275 engines, it is quite easy to become confused, or worse yet, confuse the parts-guy when it is time to order new valves! Be aware that if the head has been worked on previously, it may have oversize valves; it may have undersize if seats have been installed. Unless you are 100% sure what is in your cylinder head, it is a good idea to remove a valve for accurate measurement. There are two lengths used (nominally 3.52″ & 3.57″) three different keepers, (wide, narrow, and three-groove) and many different head diameters!