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Flat Tappets Roller Followers

Introduction to Cam Followers

 

When flat tappets are used, as shown on the left, the lobes must be tapered and the surface of the lifter is crowned.  The taper and crown are exaggerated in this image - the actual amount of crown on a flat tappet would be about 0.00005".  The purpose of the crown and taper is to cause the tappet to spin and the cam rotates under it.  With the correct geometry and surface finish and hardness, this design is very durable.  However, if the lifter stops spinning due to oil system failure or some other issue, the lifter and lobe will wear very quickly and could fail within hours.  Kams, Inc. resurfaces flat tappets with the proper amount of crown on specialty regrinding machines using diamond and CBN grinding wheels.  We monitor the profile of the crown using our Adcole CNC camshaft profile measurement machine to ensure that it is not off-center and that it is the correct shape (i.e. not too flat or too pointy, but a true arc.)

 

The right side of the diagram above shows a cam lobe and roller follower.  Sometimes the roller or both the roller and the pin are crowned.  Across a roller that is 5/8" wide, the amount of crown might be 0.00025"-0.00300".  The purpose of the crown on a roller is to reduce edge loading, and the amount of crown is intended to flatten under load so that the roller is effectively flat during operation.  Kams, Inc. has the capability to grind crowned profiles in our manufacturing and regrinding processes.

 

Note that the flat tappets are offset from the centerline of the cam lobe.  Not shown here is the difference in cam profile for a particular valve motion.  A flat tappet cam profile is more narrow and pointy than an equivalent roller cam profile, because the tappet will be engaged by the lobe sooner and will return to the base circle later as the cam rotates.  We have computer programs that we use to convert cam profiles from any cam follower type and size to any other.  We have engineered a roller cam and follower system for the Gemini industrial engines, and we are the exclusive provider of this conversion package.