Acam follower, also known as atrack follower,[1] is a specialized type ofroller orneedle bearing designed to followcam lobe profiles. Cam followers come in a vast array of different configurations, however the most defining characteristic is how the cam follower mounts to its mating part;stud style cam followers use astud while theyoke style has a hole through the middle.[2]
The modern stud type follower was invented and patented in 1937 by Thomas L. Robinson of the McGill Manufacturing Company.[3] It replaced using a standard bearing and bolt. The new cam followers were easier to use because the stud was already included and they could also handle higher loads.[2]
While roller cam followers are similar toroller bearings, there are quite a few differences. Standard ball and roller bearings are designed to be pressed into a rigid housing, which provides circumferential support. This keeps the outerrace from deforming, so the race cross-section is relatively thin. In the case of cam followers the outer race is loaded at a single point, so the outer race needs a thicker cross-section to reducedeformation. However, in order to facilitate this the roller diameter must be decreased, which also decreases thedynamic bearing capacity.[4]
End plates are used to contain the needles or bearing axially. On stud style followers one of the end plates is integrated into the inner race/stud; the other ispressed onto the stud up to a shoulder on the inner race. The inner race isinduction hardened so that the stud remains soft if modifications need to be made. On yoke style followers the end plates arepeened or pressed onto the inner race orliquid metal injected onto the inner race. The inner race is either induction hardened orthrough hardened.[2]
Another difference is that alubrication hole is provided to relubricate the follower periodically. A hole is provided at both ends of the stud for lubrication. They also usually have ablack oxide finish to help reduce corrosion.[2]
There are many different types of cam followers available.
The most common anti-friction element employed is afull complement ofneedle rollers. This design can withstand high radial loads but nothrust loads. A similar design is thecaged needle roller design, which also uses needle rollers, but uses acage to keep them separated. This design allows for higher speeds but decreases the load capacity. The cage also increases internal space so it can hold more lubrication, which increases the time between relubrications. Depending on the exact design sometimes two rollers are put in each pocket of the cage, using a cage design originated by RBC Bearings in 1971.
For heavy-duty applications aroller design can be used. This employs two rows of rollers of larger diameter than used in needle roller cam followers to increase the dynamic load capacity and provide some thrust capabilities. This design can support higher speeds than the full complement design.[2]
For light-duty applications abushing type follower can be used. Instead of using a type of a roller a plasticbushing is used to reduce friction, which provides a maintenance free follower. The disadvantage is that it can only support light loads, slow speeds, no thrust loads, and the temperature limit is 200 °F (93 °C). A bushing type stud follower can only support approximately 25% of the load of a roller type stud follower, while the heavy and yoke followers can handle 50%.[2] Also all-metallic heavy-duty bushing type followers exist.[5][6]
The outer diameter (OD) of the cam follower (stud or yoke) can be the standard cylindrical shape or becrowned. Crowned cam followers are used to keep the load evenly distributed if it deflects or if there is any misalignment between the follower and the followed surface. They are also used inturntable type applications to reduce skidding. Crowned followers can compensate for up to 0.5° of misalignment, while a cylindrical OD can only tolerate 0.06°.[7] The only disadvantage is that they cannot bear as much load because of higherstresses.[2]
Stud style cam followers usually have astandard sized stud, but aheavy stud is available for increasedstatic load capacity.[2]
The standard driving system for a stud type cam follower is a slot, for use with a flat head screwdriver. However, hex sockets are available for higher torquing ability, which is especially useful for eccentric cam followers and those used inblind holes. Hex socket cam followers from most manufacturers eliminate the relubrication capability on that end of the cam follower. RBC Bearings' Hexlube cam followers feature a relubrication fitting at the bottom of the hex socket.
Stud type cam followers are available with aneccentric stud. The stud has a bushing pushed onto it that has an eccentric outer diameter. This allows for adjustability during installation to eliminate anybacklash. The adjustable range for an eccentric bearing is twice that of the eccentricity.[2]
YOKE type cam followers are usually used in applications where minimal deflection is required, as they can be supported on both sides. They can support the same static load as a heavy stud follower.[2]
All cam followers can be track followers, but not all track followers are cam followers. Some track followers have specially shaped outer diameters (OD) to follow tracks. For example, track followers are available with a V-groove for following a V-track, or the OD can have a flange to follow the lip of the track.[8]
Specialized track followers are also designed to withstand thrust loads so the anti-friction elements are usuallybearing balls or of atapered roller bearing construction.[8]
After years of experimentation with different materials and manufacturing processes, it's developed the EZ Roll Red Zone needleless, single roller bushing design that replaces the roller needles. Isky claims "they last four times longer, and love high heat and low oil, making them perfect even for a street car idling in traffic."
Crower's new Endura Max roller lifters eliminate any chance of a needle bearing failure ruining your night and slapping you with an expensive engine rebuild. And Crower can guarantee it because it has done away with the needle bearings completely. The Endura Max lifters feature a bushed roller that utilizes high pressure pin oiling to reduce friction between the roller and the bushing. Crower says the bushed lifter allows greater load handling for aggressive camshaft profiles and are fully rebuildable.