Guy's,
Here is a topic that has been a problem for me, my customers and other people that are calling me with problems.
Cam bearing failure
I have seen this first hand. After rebuilding the engine and the cam installs nicely. Upon initial break in all goes well. After running thru the first oil change, the oil pressure starts to go down especially at idle. Sometimes the engine will be noisy.
This could be a sign of the cam bearings failing, most of the time the middle 2 of the 4 bearings are the culprits.
I blame this on material that cannot support the load. Most cam bearings are made from a Tri metal design with babbit being the top layer. The babbit layer fails and flows over the oil feed hole causing oiling loss and even worse damage. The bearing the squashes down and allows oil pressure to seep out the sides of bearing.
I have lately been using King brand bearing for the cam. They are comprised of Aluminum/ silicon and can support a much higher load.
Here is a write up from King Bearings.
Cam Bearings
Keep in mind when changing cams to pay attention to the bearings. Here is a abbreviated article from King Bearings on Cam bearing failure.
Structures and Materials of Camshaft Bearings
The typical structures and designs of camshaft bearings are presented. The most traditional design of camshaft bearings is a steel tube with a layer of lead based Babbitt alloy applied onto the inner surface (bush type camshaft bearing). The bearings of this type may be supplied in semi-finished (un-bored) condition. Then the bearings are bored after installation in the engine. However, the precision (bored) finished type is more popular. A relatively thick and soft Babbitt layer provides good conformability of the bearing. The material allows fitting its shape to misalignments. Babbitt also has very good embedability, which is important for bearings operating with contaminated oil. The main disadvantage of Babbitt bearings is their low load carrying capacity. Babbitt alloys are soft; therefore they have low fatigue strength. Also, the fatigue limit of the lining is directly dependent on its thickness: the thicker the layer the lower its fatigue limit. Since the Babbitt lining is relatively thick, its fatigue strength is low (~2,000 psi). Bi-metallic camshaft bearings, with a lining made of aluminum alloy, have a much greater fatigue strength of at least 5,800 psi. The bearings are split shells type, rather than bush. King Engine Bearings manufactures camshaft bearings made of aluminum/silicon alloy: K-788 . Their load capacity reaches 8,000 psi.
A bimetal structure with an aluminum alloy lining is the best solution for camshaft bearings. Aluminum alloy is not too hard, therefore it has good conformability. Also, it is stronger and more wear resistant than Babbitt. In contrast to a tri-metal structure, aluminum alloy bimetal bearings have superior conformability, and can tolerate far greater wear since they do not have a thin overlay. The thickness of the aluminum lining is approximately 0.010”. If the load applied to camshaft bearings exceeds the fatigue strength of aluminum alloys, tri-metal materials having a copper based intermediate layer and very thin (up to 0.0008”) soft Babbitt overlay are used. Tri-metal materials have greater load capacity, but their conformability and maximum wear are limited by the very low thickness of the overlay. Once the overlay is locally worn out and the bronze intermediate layer is exposed, seizure of the bearing by the steel journal becomes very probable. Since misalignment and excessive wear due to oil starvation are typical causes of camshaft bearing failures, tri-metal construction is rarely used in the design of camshaft bearings.
