Abstract: A wear and scuff-resistant plunger for use in high pressure fuel system components in internal combustion engines is provided. The plunger, which is formed of a high thermal expansion, high hardness ceramic with a thermal expansion coefficient preferably greater than 6.times.10.sup.-6 /.degree. C. and a hardness preferably greater than 800 Kg/mM.sup.2, maintains a desired optimum minimal diametral clearance while avoiding excessive fuel leakage and efficient plunger function without scuffing or sticking under the high axial, side and pressure loads and variable quality fuels encountered in the fuel system operating environment. Preferred high thermal expansion, high hardness ceramics are zirconia, alumina-zirconia and alumina.

Abstract: A wear and scuff-resistant timing plunger for a timing assembly in a unit fuel injector for an internal combustion engine is provided. The timing plunger is formed of a high thermal expansion ceramic with a thermal expansion coefficient greater than 6.times.10.sup.-6 /.degree. C. and a hardness greater than 800 Kg/mm.sup.2, which maintains a desired diametral clearance and efficient plunger function without scuffing or sticking under the axial, tangential and pressure loads encountered in the fuel injector operating environment. Preferred high thermal expansion ceramics are zirconia, alumina-zirconia and alumina.

Abstract: An improved cam operated, open nozzle, unit injector is disclosed including an injector body formed by a barrel, spring housing, and nozzle and containing a central bore for receiving a variable length plunger assembly mounted for reciprocal movement within the injector body wherein the variable length plunger is formed by an outer plunger and inner plunger combined with a timing plunger, mounted between the inner and outer plungers to form a collapsible timing chamber into which a variable quantity of fuel may be metered and expelled on a cycle by cycle basis to provide a variable effective length to the plunger assembly to cause controlled variation in injection timing based on variation in the timing fluid supplied to the injector and wherein the timing plunger is provided with a radial flange for engaging a stop formed in the injector barrel to hold the timing plunger in a predetermined precise location during metering of timing fluid into the collapsible timing chamber and to render the injector timing i