Piston Rings 101: Proper Break-In
If piston rings are not properly broken in, the result may be excessive
oil consumption. Compression rings rely on combustion pressures to
force them down against the bottom of the ring groove and out against
the cylinder wall. This is what makes the rings seat and seal. Initial
ring tension accounts for only a small portion of the force required to
make the rings seal. Combustion pressures account for most of the
A newly rebuilt engine must be operated under load to create combustion
pressures great enough to seat the rings. A good rule of thumb is to
operate the engine at about 75 percent of full load for the first two
or three hours. In addition, idling should be kept to a minimum,
especially during the first three hours of operation.
The oil ring acts as a metering device that leaves a controlled amount
of oil on the cylinder wall for lubrication of the compression rings.
Each compression ring removes oil from the cylinder wall to aid in
overall oil control. If compression rings do not achieve proper seating
they will not properly seal either compression or oil pressures.
Procedure for Installing Pistons on Connecting Rods
When installing pistons on rods by heating the rods, spray penetrating
oil on pistons and rods while still hot. This both protects the rods
from rust and draws the oil into the surface between the pin-boss and
the pin. Use caution since penetrating oil is flammable!
Oil Pump Installation on GM 4.3L V6 and 350 V8
The oil pumps on these engines are mounted onto the rear main bearing
cap using a single bolt. Some rear main bearing caps have a blind bolt
hole, and others are drilled all the way through (see above
illustration). Because of this, it is very important to use the correct
bolt, a 7/16"-14 x 2" bolt. If the oil pump is installed with a longer
bolt, the end of the bolt may press against the lower rear main bearing
shell and cause bearing, crankshaft and ultimately catastrophic engine
Jeltema Competition Engines,
Grand Rapids, MI
Measuring Bearing Clearance
The best way to check bearing clearance is to measure the bearing ID
with upper and lower bearing shells installed in their bores, and the
cap bolts fully tightened to the specified torque value. Once the
bearings are installed and the cap is fully tightened, measure the
installed bearing ID with a dial bore gauge or inside micrometer
(again, 90 degrees to the parting line).
Next, measure the crankshaft journal (for that specific bearing
location) with a micrometer. Subtract the journal diameter from the
installed bearing ID to determine bearing oil clearance. Note: If you
first measure crank journal diameter and then zero the dial bore gauge
to that dimension, the dial bore gauge will then directly reveal oil
clearance when measuring the installed bearings, thus avoiding the
manual calculation step.
Engine Pro Technical Committee
Half-Grooved Vs. Full-Grooved Main Bearings
Many early model engines used full-grooved main bearings (a groove in
both upper and lower shells) and some even used multiple grooves. As
engine and bearing technology advanced, bearing grooves were removed
from most modern lower main bearings. The result is a thicker film of
oil for the shaft to ride on. This provides a greater safety margin and
improved bearing life. Upper main bearing shells (which experience
lower loads than do the lower shell) have retained the oil hole and a
groove to supply the connecting rods with oil.
MAHLE Clevite Inc.