You measure across the margin of the valve for the diameter. Then measure the stem diameter and length. I would only replacwe whats damaged. Check for any abnormal wear at the keepers.

Dave

 

thank you

 

M,
Take the valve to your machine shop and see if they can figure out exactly what it is and get you the same brand for a replacement. There are variations in length and head diameter from different manufacturers. Most of the time there is a number around the top of the valve.

Also, why did it bend valves ? If there was not an obvious reason, then you need to get the guides checked to make sure thay are not too tight and sticking the valve open.