12/1/2003
Detonation in a few Ford 4.6L engines. Is this an octane issue?
We have had detonation in a few Ford 4.6L engines. Is this an octane issue?
The AERA Technical Committee offers the following information on replacement pistons for 1991-2002 Ford 4.6L VIN W, X & 6 engines. This family of Ford engines is very sensitive to an increase in compression ratio whether the increase in compression is from carbon build-up in the combustion space or changes in dimensions.
Ford’s engine control management system is calibrated for good power, mileage and clean air using the factory compression ratio. These engines are also designed to operate on low octane fuel. With that fuel they have a tendency to detonate if compression pressure is raised, they’re burning oil or overheating. When rebuilding a stock engine the compression ratio should not be increased.
Any machining operation or change of components that will ultimately reduce the cylinder combustion swept volume should be evaluated. For example, milling the cylinder head will reduce combustion chamber volume resulting in an increase in compression.
When rebuilding these engines it is advisable to use a piston with an increased dish volume to help compensate for reduced combustion chamber volume. Use of this type piston will keep the compression ratio closer to the factory-designed specification and help prevent detonation.
AERA is aware of at least one manufacturer offering pistons with an increased dish volume (approximately 4 cc’s). Increasing the dish volume allows you to keep the quench area at the correct distance while increasing the combustion space, thus lowering the compression.
NOTE: Use the correct spark plugs. If a spark plug starts to melt or is damaged but the engine heat tab is okay, go by the spark plug reading.
Is there an alternative oversize (OD) main bearing available for Cat 3406 diesels?
The AERA Technical Committee offers the following information regarding an alternative main bearing for 1973-2003 Caterpillar 3406 diesel engines. Caterpillar offers an oversize outside diameter (OS OD) bearing, which can be used for salvage operations when main bearing bores are worn.
The main bearings for all seven locations in the cylinder block are offered for standard and a .0250˝ (.635 mm) oversize OD. Those bearing pairs carry the same part numbers. Two different inside diameters (ID) are also offered, standard and a .0250˝ (.635 mm). AERA members have reported an oversize bearing also being used on original equipment engines. Use the chart above (Fig. 1) to determine the bearings required to replace OEM bearings or salvage main bearing bores. Caterpillar is the only source that we are aware of for these oversize OD bearings.
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