Clevite Main Bearings Main Bearings Set Various forms of main bearing grooving have been used over the years.
It is frequently asked what difference grooving makes.
First, it is essential to understand that bearings rely on a film of oil to keep them separated from the shaft surface.
This oil film is developed by shaft rotation.
As the shaft spins, it pulls oil into the loaded bearing area and rides up on this film much like a tire hydroplaning on wet pavement.
Grooving in a bearing acts like tread on a tire to break up the oil film.
While you want your tires to grip the road, you don't want your bearings to grip the shaft.
The main reason to have any grooving in a main bearing is to provide oil to the connecting rods.
Without rod bearings to feed, a simple oil hole would be sufficient to lubricate the main bearing.
Many early engines used full grooved bearings and some even use multiple grooves.
As engine and bearing technology developed, grooving was eliminated from modern main bearings and lower bearings.
The result is a thicker oil film for the to ride shaft.
This provides a greater margin of safety and improved bearing life.
Upper main shells, which see lower loads reduced, have retained a groove to supply the connecting rods with oil.
In an effort to develop the best possible main bearing designs for performance engines, the effects of main bearing grooving on bearing performance have been investigated.
The graphs on the next page illustrate that a simple 180 groove in the top of the main shell is still the best overall design.
While a slightly shorter 140 groove offers a marginal gain, the majority of the benefit is to the top of the shell, which doesn't need improvement.
On the other hand, extending the groove in the lower half, even as little as 20 in each metal line (220 in total), takes away from superior bearing performance without providing any benefit to the lower half.
It is also interesting to note that as groove length increases, so does oil power loss and peak film pressure.
