 You'll need a proper service manual, a metric feeler gauge, a micrometer and–for Fiats–the proper shim removal tool. Start by filling out a chart like this (these numbers are from a typical 4-cylinder Alfa; the concept is similar for Fiats):
Consulting your manual, first write in the factory-recommended clearances in the “correct clearance” column. Next, following the procedure in the service manual, measure the clearance between the heel of each cam lobe and its tappet, and record your findings in the “current clearance” column. Then compare these measurements with factory specs and record the variance in the +/- column. Now, measure the thickness of the existing shim with your micrometer, recording this in the “current shim” column. Add or subtract the value in the +/- column to (or from) the current shim size. The resulting figure is the shim needed to restore proper clearance. Round up or down to the nearest size. Alfa shims are graduated in .025mm steps, Fiat shims in .05mm steps. If a valve is split evenly between two sizes, round downward (it's safer to have a valve a bit too loose than too tight). |
