The end-play or thrust clearance of the camshaft(s) must be measured with the camshaft installed in the head. In most cases it may be checked before removal or after reinstallation. To check the end-play, mount a dial indicator accurate to ten one-thousandths (four decimal places) on the end of the block, so that the tip bears on the end of the camshaft. The timing belt or timing chain must be removed. On some motors, it will be necessary to remove the sprockets for unobstructed access to the camshaft. Set the scale on the dial indicator to zero. Using a prytool, gently lever the camshaft fore-and-aft in its mounts. Record the amount of deflection shown on the gauge and compare this number to the Camshaft Specifications Chart.
If the camshaft has a removable thrust case, the case must be reinstalled to the end of the camshaft and the bolt tightened. Check the end-play with a feeler gauge. If the end-play is excessive, replace the thrust case with a new one and recheck the clearance. If the end-play is still excessive, replace the camshaft.
Excessive end-play may indicate either a worn camshaft or a worn head; the worn camshaft is most likely and much cheaper to replace. Chances are good that if the camshaft is worn in this dimension (axial), substantial wear will show up in other measurements.
Using a micrometer or Vernier caliper, measure the diameter of all the journals and the height of all the lobes. Record the readings and compare them to the Camshaft Specifications Chart in the beginning of this Section. Any measurement beyond the stated limits indicates wear and the camshaft must be replaced.
Lobe wear is generally accompanied by scoring or visible metal damage on the lobes. Overhead camshaft engines are very sensitive to proper lubrication with clean, fresh oil.
If a new camshaft is required, order new rockers to accompany it so that there are two new surfaces in contact.
The clearance between the camshaft and its journals (bearings) must also be measured. The amount of space between the camshaft and its bearings is the oil clearance; less space means less oil and more wear. Excessive play will allow the camshaft to hammer the bearing and cause wear. Clean the camshaft, the journals and the bearing caps of any remaining oil and place the camshaft in position on the head. Lay a piece of compressible gauging material (Plastigage® or similar) on top of each journal on the cam.
Install the bearing caps in their correct order and install the rocker assembly. Tighten the bolts in three passes to the correct torque.
WARNING
Do not turn the camshaft with the gauging material installed.
Remove the rocker assembly and measure the gauging material at its widest point by comparing it to the scale provided with the package. Compare these measurements to the Camshaft Specifications Chart. Any measurement beyond specifications indicates wear. If you have already measured the cam (or replaced it) and determined it to be usable, excess bearing clearance indicates the need for a new head due to wear of the journals.
Remove the camshaft from the head and remove all traces of the gauging material. Check carefully for any small pieces clinging to contact faces.
After a careful cleaning, coat the camshaft and bearing surfaces with clean engine oil and continue reassembly.