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Engine Builder Shop Solutions, December 2007

Piston Rings 101: Proper Break-In; Procedure for Installing Pistons on Connecting Rods; Oil Pump Installation on GM 4.3L V6 and 350 V8; Measuring Bearing Clearance; Half-Grooved Vs. Full-Grooved Main Bearings

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 force.

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.

Engine Pro
Technical Committee

 

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!

Darrin Anderson,
Braymer, MO

 

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 failure.

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.

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