I had a set of coated ones in my last build that did good even though I had to scrape #4 to fit it for my cam, but I can't remember the manufacturer. I just put in a set of FM, and I am going to take them back out. Just don't like the way they felt going in, and had too much trouble with them.
The FM does have smaller oil holes than the coated ones, and I like that. It lets more of the oil supply go where the real stresses are. Cam bushings don't have a terrible hard life but they can cause you a heap of grief.
Re:The wear pattern in those cam bearings in the picture. Clevites bearing failure Analysis guide(which is specific to insert halves) calls this Surface Fatigue and says that most likely in your case it is due to either inadequate fatigue strength for the application or the service life was exceeded.
Here is the only place they address cam bearings in particular
For many years, nearly all camshaft bearings were manufactured with a lining of babbitt. Babbitt is a soft
slippery material made up primarily of lead and tin and is quite similar to solder. As a bearing surface layer,
babbitt possesses the desirable properties necessary to survive under adverse conditions such as foreign
particle contamination, misalignment and marginal lubrication on start up.
The trend in modern engines has been toward higher operating temperatures and higher valvetrain loads. Babbitt
is limited in its ability to survive under these conditions due to its relatively low strength. When babbitt cam bearings
are installed under these demanding conditions, the lining may extrude or fatigue. Fatigue can be identified by
craters in the bearing surface where sections of lining material have flaked out.
To meet the demands of higher loads and operating temperatures in modern engines as well as the requirements
imposed by high performance, babbitt has been replaced by an alloy of aluminum. This aluminum alloy is much
stronger than babbitt and will withstand several times the load. However, this added strength is obtained at the
expense of some of the more forgiving properties of babbitt. The aluminum alloy is harder, making it somewhat
less compatible with dirt, misalignment and marginal lubrication. This is typical of the compromises or trade offs
that are frequently necessary when selecting a bearing material to suit the requirements of a specific application
and in this case, higher loading.
Typically, whenever a higher level of loading is encountered, greater precision is required to maintain reliability.
Conditions such as cleanliness, alignment, clearances, journal surface finishes and lubrication must all be controlled
more closely. Following are some recommendations to help optimize performance when using aluminum
alloy camshaft bearings.
Sufficient clearance is necessary in the initial installation. These stronger bearings will not wear in rapidly to make
their own clearance like softer babbitt materials. Minimum clearance should be .002” for stock engines and .003”
for high performance. Optimum clearance range for high performance applications is .003” to .004”. Because of
the stack up of tolerances on the block, shaft and bearing it is impossible to control clearance to this range in the
manufacture of the bearing alone. Clearances must be measured at installation.
Honing the ID’s of cam bearings to increase clearance is not recommended because hone grit may become
embedded in bearing surfaces that will cause shaft wear. Bearing ID’s may be reamed, but the most practical
means is to adjust camshaft journal diameters by grinding the journal. Even if not ground to provide additional
clearance, camshaft bearing journals should be polished to the proper surface finish with the camshaft rotating in
the same direction it will rotate in the engine.
Like clearance, alignment is also extremely important especially for high performance applications. Any block that
has needed to have its main bearing bore alignment corrected due to distortion is likely to have experienced cam
bearing bore distortion as well. Adequate clearance can help compensate for minor misalignment of less than
Installation of bearings into the block must be done with care to avoid shaving metal off the backs of the bearings.
This galling action may cause a build-up of metal between the bearing OD and the housing bore which will result
in a reduction in clearance. To prevent galling, check housing bores for a proper 25 to 30 degree lead-in chamfer
before installing cam bearings. On blocks without grooves behind the cam bearings, care must be taken to insure
that oil holes line up between the bearings and block. Where the block has a groove behind the bearing, the
bearing should be installed with the oil hole at the 2 o’clock position when viewed from the front for normal clockwise
camshaft rotation. This will introduce oil into the clearance space outside of the loaded area and allow shaft
rotation to build an oil film ahead of the load.
Cam Bearing Failure
Engine Bearing Failure & Analysis Guide
©2002 Dana Corporation Printed in U.S.A.
Ask your Clevite Sales Representative about our many other quality Clevite engine parts.
1350 Eisenhower Place
Ann Arbor, MI • 48108 • U.S.A.