Piston assembly 320/09421 JCB Dieselmax DE standard, genuine

Piston assembly 320/09421, standard is a genuine JCB part for the JCB Dieselmax (DE) engine.

The piston passes combustion pressure through the rod to the crankshaft; the rings seal the combustion chamber and control the oil film on the bore. In a turbocharged engine the crown works at high pressure and temperature, so ring wear shows as blue smoke, oil consumption, low compression and more blow-by from the breather. The gudgeon pin is fully floating and held by two circlips. The Dieselmax is a direct-injection engine: fuel is injected into the bowl in the piston crown and combustion starts there. Pistons in one engine should be close in weight, so when a single piston is replaced the weight difference is checked too. The piston pin and rings are checked together with the piston. The piston is cast from aluminium alloy and joins the rod through the gudgeon pin. The piston is supplied new.

Specifications

Compatibility

The part is listed for JCB 3CX and 4CX backhoe loaders. The catalogue also has the aftermarket version of this part. Other parts are in JCB Dieselmax engine.

Fitting

Before fitting, the bore is honed and cleaned; the piston and rings are oiled and pushed in with a ring compressor. Piston protrusion above the block is measured to check the head gasket thickness. After assembly the engine is run in at light load. After assembly, compression can be measured to compare the cylinders. Fit the pistons to the rods by their direction mark.