[CaliMX]

Where do I start...
First of all you need to try and make an educated guess on why the valve broke to begin with, excessive valve guide wear, valve was shimmed to many times, valve float, etc. Check the valve to valve guide clearance carefully.
When you do a complete head rebuild with all new valves, springs, etc. you have to cut the valve seats to match the seating surface of the valve perfectly, if you match new valves with worn beat up seats the new valves will not last very long at all, the seats may look OK to the naked eye but they will not be perfectly round and the seating surface angle changes over time from the old valves moving and being reshimmed, not to mention when you use new valves without cutting the seats you will not get a good seal and you'll loose some compression. The issue is not with the valves it's with the valve seats and/or the valve guides. You will learn this more in depth at MMI.