I am working on resurrecting a Snapper mower with a 16 HP Tecumseh engine that the intake valve seat popped out of. The seat had been "peened" back in once before I acquired the mower, hence the cheap price of $75 I paid for it. I peened the valve seat back in, & lapped the valves, & put everything back together. She runs fine, but the exhaust pipe running to the muffler is glowing cherry red. I am thinking the valve is not seating properly allowing combustion to happen in the exhaust. I have acquired another head with the seats in factory condition, & have lapped both valves. I have read (after installing the old head) that to test the seal on the valves you spray wd40 into the chamber & apply air with a rag around the entrance to help seal everything. Doing this the intake valve doesn't allow any liquid to pass, but the exhaust has tiny bubbles around it. I have lapped the exhaust 3 times now with both coarse and fine compound & have a nice smooth ring all the way round. Should I just install it & run it a while to see what happens? At this point I really don't know how to proceed. An help would be greatly appreciated!
Are you sure that the seats have been cut to 46 degrees and the valve faces are cut to 45 degrees. Second after lapping is the lapping ring in the center of the valve face and and cover no more than 1/3 the width of the valve face. A wide lapping ring has a tendency of leaking more than a narrow ring.
I am not sure about the angle as this is a head from a junkyard. The ring is quite wide though. How could I decrease the width? I work in a machine shop and could put it on the lathe & reface the angle & relapse then I suppose?
