Nanni T4.155 seriers, Workshop Manual

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C. Clean valve guide bushes
Use a valve guide bush brush and a solvent to carefully clean the valve
guide bushes.
D. Clean the cylinder head
Use a flexible bristle brush and solvent to carefully clean the cylinder
heads.
3. CHECKING THE CYLINDER HEAD
A. Check flatness
Use a precise straight edge and a set of thickness shims to measure the
contact clearance of the surface between the cylinder block and the
manifolds, and to detect any possible warping.
Maximum warping: 0.15 mm
If warping is higher than the maximum dimension, replace the cylinder
head.
B. Check for cracks
Use a dye and examine the combustion chambers, intake slots, exhaust
slots and the cylinder block surface to detect any cracks.
Replace the cylinder head if cracks are found