why do we lap valves so often?.....because there is leakage between the valve and the seat. So, some racers will also cut the valve seat and then lap the valve. Why do we have to cut the valve seat....what is causing it to need to be cut? The culprit is the exhaust valve guide being worn. These guides are made of sintered steel which is nothing but pressed powder, and don't take heat very well. When the valve guide wears, the valve will not seal on the valve seat. Lapping the valve will not cure the problem.....cutting the seat will not cure the problem. Briggs realized they had a heat problem and their band aid was to raise the exhaust guide out of the exhaust port to help cool it. Then, they came up with the "Heat Disperser" to help with the heat problem. The Intake is no problem because the Intake guide is down in the Intake port and the fuel/air mixture cools the intake guide. The exhaust guide needs replaced. When you remove the valve spring...push the valve up a little and check the wear by moving the valve back and forth. If it moves sideways more than a couple thousands....it's worn and needs replaced. Now.....when you remove the guise, don't hammer the guide out, use a press. These heads are cast aluminum....Chinese cast aluminum at that, so beware. Before you press the new guide in, it will have to be reamed, and the best way is to use a lathe. Using a .2485 chucking reamer, ream it with cutting oil. Clean with brake kleen and press into the head. DO NOT PRESS IN TOO FAR, just to the groove on the guide. Using WD40, and a .250 flex hone, run the hone thru a few times...don't over do it. Now that you have a new exhaust guide in place, you will have to cut the seat to match the new guide. Take light cuts and keep checking by putting in the valve and holding up to light to make sure you see no light coming in around the valve and seat. After you cut the seat..THEN lap the valve to seal . See....wasn't that easy? Unless you have the proper tools to do this, I suggest having an qualified engine builder or machinist do this for you. Hope this helps everyone. If I can be of any help to anyone, I do these heads all the time. You can PM me. Some will say, "I'll just buy a new head!" The head you have is already heat cycled so hang on to it.