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

Piston assembly 320/09238, +0.50 mm is an aftermarket part for the JCB Dieselmax 444 engine.

Piston life depends heavily on the air filter and fuel system: dust passing the filter wears the rings and bore, and a faulty injector burns the crown. That is why the air filter and injectors are checked when pistons are replaced. The combustion bowl shape and compression height are set by the engine version. 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 genuine version and OEM version of this part. For this size there is also the +0.50 mm ring set. Other parts are in JCB Dieselmax engine.

Fitting

Pistons are replaced in all four cylinders at once. Before assembly the bores are measured for size and ovality, the ring gaps are staggered and each piston goes in with its mark towards the front of the engine. The big-end bearings and head gasket are renewed during the same strip-down. After assembly, compression can be measured to compare the cylinders.