Piston assembly 320/09421 JCB Dieselmax DE standard, aftermarket

For the JCB Dieselmax (DE) engine: piston assembly 320/09421, standard, an aftermarket part.

The piston size follows the bore: a standard piston for an unmachined bore, an oversize piston after the bore has been machined and honed. The combustion bowl in the crown and the ring grooves differ between engine versions, so the piston is selected by engine code and part number. Scoring, a burnt crown or a broken ring land call for a new piston. 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 genuine version of this part. Other parts are in JCB Dieselmax engine.

Fitting

When fitting the gudgeon pin the piston can be warmed slightly in warm oil; the pin must go in without force. Seat the circlips fully in their grooves. During the first hours after assembly, watch the oil level and exhaust smoke. After assembly, compression can be measured to compare the cylinders. Fit the pistons to the rods by their direction mark.