Before servicing or repairing a valve, use the valve spring compressor from DYI, together with adapter 6716A, to compress the springs. Take away the valve retaining locks, retainer springs, valve stem seals and valve springs. Before you remove the valves, get rid of any burrs on the lock grooves and figure out their exact locations so you put them back where they belong. After putting lubrication oil on the stems, fit the valves into the cylinder head. If you've had threaded valves, make sure they aren't too tall; they must be replaced if they are too tall. Put valve springs and valve retainers on next, right after you have replaced the guides for the valves. Set up the valve springs a second time, this time using the adapter 6716A with the Valve Spring Compressor Tool and then install the locks and free the tool. With ground valves and seats, use a micrometer to find the distance between the bottom of the spring seat in the head and the bottom of the spring retainer or from the top of the spacer if using them. When height is greater than 42.86 mm (1-11/16 inches), add a 1.587 mm (1/16 inch) spacer into the spring's head counterbore to reduce its total height back down to 41.27 to 42.86 mm (1-5/8 to 1-11/16 inches).