Piston assembly 320/09249 JCB Dieselmax SD standard, OEM Nural

For the JCB Dieselmax 444 (SD) engine: piston assembly 320/09249, standard, an OEM part made by Nural. The card also lists 87-73859STD. The Nural number is 87-73859STD.

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 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 genuine 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

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.