engines by nissan that use shim lash adjusters have a difficult time obtaining shims when you adjust valve clearance after an overhaul, valve grind or replacement of camshafts. to avoid this predicament not having the right thickness of thinner shims, check the clearance before installing the cylinder head/s. this way, should the thinner shims are unavailable, you can remove the valve and trim the valve stem to accomodate the shim providing the right lash. the shims are hard to find in the u.s. mainland and, believe it or not, in yokohama where nissans are made