Whenever racers or engine builders tear down an engine for a rebuild and see damage to the main or rod bearings, one of the first assumptions is that the bearing clearance wasn't sufficient. Obviously, if you've got a main or rod journal rubbing a bearing, the fix is to add more room for the oil to cushion between the two components, right? Not necessarily.
Ron Sledge of King Engine Bearings reminded attendees that tightening bearing clearances can often help the oil do its job better. Tighter bearing clearance can actually reduce the peak bearing loads because the smaller space the oil had to fill makes the oil film act stronger. The result is better distribution of the loading over a larger area. Now the oil is better able to hold the journal away from the bearing because the loading is distributed better.
Tighter bearing clearances can also be the solution if you are noticing bearing pitting. Pitting normally happens when you have aeration, or small bubbles of air, of the oil. When the oil is under pressure the air bubbles are compressed, and when that pressure is reduced the bubbles expand. In a race engine with a high rpm range any area where the pressure is reduced can allow any bubbles that are in the oil to practically explode, severely reducing your oil's ability to protect the bearing. This is how pitting often forms on the bearing babbit. Tightening the bearing clearance helps hold the oil pressure higher in that area, keeping any aeration in check until the oil exits the bearing.
This isn't a hard and fast rule because it certainly is possible to have your bearing clearances too tight, but it definitely is a point to consider if you are puzzling over the cause of bearing damage found.
New Camshaft Tech
One of the biggest advancements in camshaft development for the last several years is Comp Cams' new Four Pattern camshafts. You likely saw the Quick Tech on these cams in last month's issue of Circle Track but Comp's Billy Godbold provided the lowdown on these cams for the gathered engine builders. Multi-pattern cams are nothing new in the racing industry, but by utilizing CNC technology, Comp has finally found a way to make them affordable for the Saturday night racer.
Using much of the R&D they had invested into Cup racing engines (they are no longer used thanks to fuel injection) Comp has been able to develop four-pattern cams that produce approximately 1 to 2 percent more power throughout the rpm range on engines with a common plenum. This is done by using the cam to compensate for the differences created by the long and short runner splits to create a more consistent air/fuel balance from cylinder to cylinder. Besides the increase in power, Godbold says the new cams can also create a better response at low rpm without the typical fall-off in the upper rpm range. They are also less sensitive to weather changes. Right now all the new four-pattern cams are for use with hydraulic lifters, but we expect to see more race oriented solid lifter cams soon.