Tech Tip - Early 4 Cam Failure
By: Gary Bobileff
Anybody who has owned a Dino, 275/4 cam, Daytona, or 365 GTC/4 has had or will have camshaft failure. During this generation of cars, Ferrari had changed their designs in camshaft construction. All of the above mentioned cars had the "new generation" style cams which differ in design to earlier cars because they run four overhead cams and no longer use a "roller and axle" design to open the valve. The four cam motors have the cam lobe rub against a hardened valve shim. These shims are available in varying thicknesses, therefore allowing valve adjustment by simply inserting the proper thickness shim in a holder, known as a cam follower (tappet). See Fig 1 (as per the 365 GTC/4 owner's book).This design proved to be very reliable, light weight, and silent but there was one major problem. It was found that after about 20,000 miles on the average, the lobes of the cams would start to wear. When this happens, metal is being removed from the lobe, and gets circulated in the engine oil. The lobe changes shape and becomes sharp edged and as it rubs on the shim during each revolution, which affects performance. It also scratches and scores the shim's rubbing surface. The hardness is then broken through on the surface of the shim and it too begins to deposit metal in the oil. Valve clearance increases rapidly at this time, valve noise increases and performance becomes poor.
Caption .
How can the problem be fixed? Two ways. The most difficult and expensive is to replace the cams with new ones (if available). The other way is to send the cams to a reliable cam grinder for repair. The grinder must have or make masters of the cam in order to duplicate the original cam lobe shape and size and do a proper refinishing job. First, because the cams are hardened, they must be annealed (softened), then the damaged lobes may be reprofiled and polished if there is only light damage. If the lobe is badly damaged, the lobe is ground down, welded with a high nickel content rod, ground to its proper shape, polished, heat treated for strength, straightened, and reinstalled. Depending upon how badly damaged the cams are, the typical cost will vary from $100 to $300 per cam just for reconditioning. Proper installation is even more fun!
Every time the valves are checked for adjustment, the cam lobes should be carefully inspected for possible present or future damage. Observe and compare the shape of each lobe. Also, feel the tip of the lobe. It should be smooth and should not have any sharp edges or distressing in the tip.
Ferrari changed it's hardening process with the 365 BB, 208 and 308 motors. It is very rare to see one of these later motors with cam damage.
About the author: etc Located in San Diego, Gary Bobileff has been a Ferrari addict since 1970, servicing and restoring them exclusively. If you have any technical questions, feel free to call him at (619) 622-1600.
For a complete look at Sempre Ferrari, you may want to check out the rest of the articles from Volume 1, Issue 3 - August 1994