When renewal becomes necessary the valve guides can be removed from their positions in the head by driving them outwards from the ports towards the rocker cover faces. Heat up the heads evenly before removing the guides, and use a brass punch of just under 3/8-in. shouldered down for a distance of 3/8-in. at one end to just under 7/32 -in. Transfer the circlips to the new guides, or fit new ones, locating them carefully in the grooves. These grooves are not exactly midway along the guides and the longer portion in each case goes into the valve guide hole in the head.
Heat up the head before fitting, and use the shouldered punch to prevent damage being done to the guides.