Piston assembly 320/09258 JCB Dieselmax SD +0.50 mm, OEM Nural

For the JCB Dieselmax 444 (SD) engine: piston assembly 320/09258, +0.50 mm, an OEM part made by Nural.

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.

Specifications

Compatibility

The part is listed for JCB 3CX and 4CX backhoe loaders. The piston is used on the SD-coded Dieselmax 444 after the bores have been machined 0.50 mm oversize; for standard bores choose the piston 320/09249. The catalogue also has the genuine version and aftermarket version of this part. An oversize piston is used together with rings of the same size. 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.