A Little Inside Information

Many cam profiles are used incorrectly.

Cam profiles are designed for a specific set of parameters. Some of the basic parameters are the base circle diameter of the lobe, the diameter of the flat tappet or the roller wheel diameter, and whether a hydraulic or a solid tappet is used.

One common misuse of a cam profile is the base circle diameter. A cam grinder will often grind a camshaft with small base circle diameter lobes in order for the lobes to clear the connecting rods or something else in the engine. The problem is that the original cam profile was designed for a full size base circle diameter. On a flat tappet camshaft the smaller lobe will also have a smaller radius at the nose of the lobe. This will definitely cause premature wear. On a roller camshaft the smaller lobe will cause an increase in the pressure angle between the roller wheel and the lobe. This will cause premature wear on the roller wheel bearing. The smaller lobe will also lose duration compared to the original design.

Cam profiles are designed for a specific flat tappet diameter or a roller wheel diameter. If a smaller flat tappet diameter is used then the contact point will move off the edge of the tappet and cause immediate wear. A larger diameter tappet can be used but with a potential loss in performance since the original cam profile was not designed for the larger diameter tappet. If a different diameter roller wheel is used then the entire original cam profile is changed causing the engine to perform differently from what was expected. Mechanical damage can also occur.

Cam profiles are designed for either a hydraulic or a solid tappet. Poor performance and mechanical damage can occur if they are interchanged.

By not using the correct cam profile design, lack of performance and reliability problems will occur. In order for the camshaft to perform at its best, properly designed cam profiles for the application must be used.

There are several reasons why cam profiles are used incorrectly:

• lack of knowledge (some cam grinders just don't know any better)

• nothing will be damaged so it's ok (some cam grinders will knowingly use the wrong profile and hope for the best)
• not having enough information about the cam profile used (cam grinders will sometimes copy cam lobes without knowing the original design data)
• not having the correct cam profile designs (some cam grinders just don't have the correct cam profiles and will use what they have)

Not all cam grinders have the ability to design cam profiles. Be sure and ask your cam grinder where the profiles on your camshaft came from.