Piston assembly 320/09238 JCB Dieselmax +0.50 mm, genuine

Piston assembly 320/09238, +0.50 mm is a genuine JCB part for the JCB Dieselmax 444 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.

Specifications

Compatibility

The part is listed for JCB 3CX and 4CX backhoe loaders. The oversize piston goes in after the bores have been machined 0.50 mm oversize and honed; all four bores must be the same size. The catalogue also has the OEM version and aftermarket version of this part. For this size there is also the +0.50 mm ring set. 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.