Individual Main Bearings
Various forms of main bearing grooving have been used over the
years. We are frequently asked what difference grooving makes.
First, its essential to understand that bearings depend on a
film of oil to keep them separated from the shaft surface. This oil
film is developed by shaft rotation. as the shaft rotates it pulls
oil into the loaded area of the bearing and rides up on this film
much like a tire hydroplaning on wet pavement. Grooving in a
bearing acts like tread in a tire to break up the oil film. While
you want your tires to grip the road, you dont want your bearings
to grip the shaft.
The primary reason for having 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 a main
bearing. Many early engines used full grooved bearings and some
even used multiple grooves. As engine and bearing technology
developed, bearing grooving was removed from modern lower main
bearings. The result is in a thicker film of oil for the shaft to
ride on. This provides a greater safety margin and improved bearing
life. Upper main shells, which see lower loads than the lowers,
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, weve investigated the effects of main
bearing grooving on bearing performance. The graphs on the next
page illustrate that a simple 180 groove in the upper main shell is
still the best overall design.
While a slightly shorter groove of 140 provides a marginal gain,
most of the benefit is to the upper shell, which doesnt need
improvement. On the other hand, extending the groove into the lower
half, even as little as 20 at each parting line (220 in total),
takes away from upper bearing performance without providing any
benefit to the lower half. Its also interesting to note that as
groove length increases so do horsepower loss and Peak Oil Film
Pressure which is transmitted directly to the bearing.
These are not to be confused with the standard passenger car and
light truck parts for the same retention applications which also
have a P suffix letter. These high performance parts have unique
core part numbers different from the standard parts for the same
application. P-Series parts are the oldest series of Clevite high
performance bearings. The rod bearings in this series typically
have the greatest amount of eccentricity. Most rod bearings are
available either with or without dowel holes for use in aluminum
rods. Most P-Series main sets are full grooved to maximize oil flow
to the rod bearings. Both rods and mains have high crush for
maximum retention, and a reduced overlay thickness to prevent
overlay fatigue, sometimes referred to as hen tracking.
Rod bearings use a hardened steel back for added strength and
resistance to fretting. Extra clearance rod bearings are available
for .001 additional clearance and select fitting. Use the P-Series
rods where extremely high RPMs cause severe rod bore close-in. This
is typically indicated by nearly full parting line to parting line
shaft contact with bearings having less eccentricity. Use P-Series
mains where higher eccentricity is desired to narrow bearing
contact patterns and to provide increased oiling to rod earings.
Rod bearing oil starvation is typically indicated by polishing and
smearing of the bearing surface, possibly accompanied by
discoloration predominantly concentrated at the axial center of the
These bearings are identified by a letter H in the part number
suffix. Part numbering is based on the same core number as the
standard passenger car parts for the same application. These
bearings were developed primarily for use in NASCAR
type racing, but are suitable for all types of competition
H-Series bearings have a medium level of eccentricity, high
crush, and rod bearings have a hardened steel back and thin
overlay. These bearings also have enlarged chamfers for greater
crankshaft fillet clearance and are made without flash plating for
better seating. Bearings with .001 extra clearance are available
for standard size shafts and carry the suffix HX (X = extra
clearance). Rod bearings are available with or without dowel holes
(HD = with, H = without), main bearings are available
with standard 180 degrees upper half grooving and with full 360
degrees grooving (H = 180 degrees, HG 360 degrees).
Use H-Series bearings with crankshafts that have oversize fillets
and where engines run in the medium to high RPM range.
H-Series bearings should be used if contact patterns obtained with
P-Series parts are too narrow. Contact patterns should ideally
cover 2/3 to 3/4 of the bearing surface. See accompanying contact
pattern diagrams. If you arent sure which type of performance
bearing to start with, the H-Series bearing will be your best
These bearings are identified by a letter K in the part number
suffix. Part numbering is based on the same core number as the high
performance part and will service the same application. These
bearings were developed primarily for high performance applications
and all types of competition engines. K-Series bearings have a
proprietary moly/graphite treatment applied to the bearings
surface, but not the bearing parting lines. The PTFE
carrier material gives good low load start-up protection. The moly
serves as a high pressure, high load dry film anti-wear agent.
Graphite provides additional protection across the broad range of
temperatures, especially when oil flow is marginal and is
especially slippery with an oil film. These bearings, which are
also referred to as TriArmor, still offer the strength and
durability of the legendary Clevite TriMetal bearing construction
coupled with the latest in coating technology.
These parts essentially duplicate the former Vandervell parts under
the Clevite part numbering system. (Same core part no. as standard
passenger car parts but with a suffix letter V).
V-Series rod bearings typically have low to medium eccentricity
and a hardened steel back. All V-Series main sets use a single
piece thrust bearing rather than the former Vandervell assembled
type of construction. V-Series parts are not available with
oversize chamfers. Extra clearance parts are available with a
suffix VX (.001 extra clearance), and VXX
(.002 extra clearance) for some applications. V-Series bearings do
not have flash plating on the steel back. Narrowed parts are
available with a VN suffix for some applications.
These are made to accommodate increased crankshaft fillet
The chief difference between the V-Series and other Clevite
TriMetal bearings is the use of lead-indium overlay. Use V-Series
bearings if prior experience has shown a preference for the
lead-indium type of overlay. Lead indium overlay offers somewhat
better conformability than leadtin-copper overlay with slightly
reduced wear resistance.
Clevite Micro bearings make up the M-Series. These are special
purpose bearings having a nominal .006 thick babbitt lining on a
hardened steel back. M-Series rod bearings have been slightly
narrowed at one end to provide extra fillet clearance without the
need of a large chamfer. The lower rod shells have a dowel hole for
use in aluminum rods with dowel pins. M-Series mains have enlarged
chamfers and, for certain applications, oil holes and oil grooves
have also been enlarged.
Use M-Series parts to take advantage of the high degree of
conformability offered by the babbitt lining. These parts are
intended mainly for engines where severe crankshaft deflections
cause edge loading of the bearings. Under these operating
conditions bearing service life will be very short.
Frequent inspections are recommended and bearings should be
replaced at the first signs of distress.