Mercury YS4Z-6505-AA Exhaust Valve

If valve clearance is out of spec, adjust by replacing the shim. Smaller clearance needs a thinner shim, larger needs a thicker one. Formula: New shim thickness (D) = C + (A - B), where A = specified clearance, B = measured clearance, C = current shim thickness. Example, clearance too small: A = 0.15 mm, B = 0.09 mm, C = 2.55 mm, D equals 2.49 mm, use 2.49 mm shim. Example, clearance too large: A = 0.30 mm, B = 0.36 mm, C = 2.19 mm, D equals 2.25 mm, use 2.25 mm shim. Measure with engine cold, recheck after installation, and use quality shims for accuracy.