Extending dipper cylinder barrel 556/70339 JCB 3CX/4CX, aftermarket

Extending dipper cylinder barrel 556/70339 is an aftermarket part for the JCB 3CX and 4CX backhoe loaders.

A cylinder barrel is the steel tube with a precisely finished bore in which the piston works. The barrel carries the mounting eye or trunnions, the ports and, on most cylinders, a pipe along the body that takes oil to the rod side. The barrel is replaced when the bore is deeply scored, dented by an impact or the eye is worn; a scored bore soon ruins the piston seal and the cylinder starts to leak past under load. When the barrel is renewed, the old rod, piston and gland can be reused if they are in good order, while the seal kit is always replaced. That makes a barrel a cheaper repair than a complete cylinder. Corrosion in the bore also damages the seals, and machines that have stood idle for a long time often show rust marks in the barrel. When the new barrel is fitted, check the bush in the mounting eye too and renew it if worn. Choose the barrel by part number and compare it with the old one.

Specifications

Compatibility

The barrel belongs to the extending dipper cylinder. Other parts are in JCB hydraulic cylinders.

Fitting

Do not use sharp tools when fitting the seals; fitting cones and clean oil help the seals go in without damage. Check the lip direction of the new seals against the old ones, since a seal fitted the wrong way round leaks at the first pressure.