RB25 conversion Stage 5 - Lapping the valves and painting the block

Now the head has been stripped down it's time to get the valves lapped in so they give a nice seal. The first thing to do was to remove the valve stem oil seals. I used a pair of needle nose pliers and gently squeezed and worked the seals until they cracked loose from the guide and then worked them off the guide. They are a tight fit so you need to give them a good pull to get them off. The Nissan part number for ordering another set is 13207-84A00, all 24 are the same. Here's the seals removed from the head and the new set I ordered...

With the seals out the valves will rotate easily within the guides. To lap a valve you need a valve grinder (a stick with a plunger on the end which sticks to the valve head by suction) and some coarse and fine grinding paste. Start off by putting some coarse paste on the valve around the valve to valve seat mating surface. Put the valve in the port, and then roll the grinder between your hands. After a few grinds, turn the valve one quarter turn and repeat. You can feel the difference when the paste has done it's cutting. Remove and check the seat and valve, and it should be looking much cleaner/smoother. Next apply some fine paste and repeat the process. When grinding valves less is more - you only want to clean and smooth the surfaces so you get a good seal. Don't cut too far into the head as this will knock all the shim measurements out. Here's a valve with fine cutting paste applied before grounding...



And the valve seated in the head with the grinder attached about to be ground...



Here's 2 exhaust valves, one before being cleaned and lapped, and the other after...




And the same with 2 inlet valves...




Here's a combustion chamber with inlet and exhaust seats lapped on the left, and unlapped on the right...



And close-ups of the 2 lapped seats...




Once the valves were all lapped in, I took a trip to Halfords and bought some bright red engine enamel to paint the block and cylinder head. I wire brushed the block and cleaned it with some Gunk engine cleaner. The block took 3 coats, but looks really nice and clean now :o)...




Next weekend I'll be painting the cylinder head. Stay tuned!