Piston assembly 320/09249 JCB Dieselmax SD standard, genuine

Piston assembly 320/09249, standard is a genuine JCB part for the JCB Dieselmax 444 (SD) engine. The photo shows the piston with its rings.

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.

Specifications

Compatibility

The part is listed for JCB 3CX and 4CX backhoe loaders. The SD code marks the Tier 3 turbo version of the Dieselmax 444; check the serial number on the engine plate. The catalogue also has the OEM version, aftermarket version (option 1) and aftermarket version (option 2) of this part. For standard bores there is the piston ring set 320/09299. 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.