Abstract: The chain tensioner has a housing with a first part that defines a bore which receives a second part that is tubular. The second part has a bore which receives a plunger. A check valve is disposed in the housing for controlling the delivery of a hydraulic fluid into the bore of the housing. A fluid passage is defined between the first and second part as a helical groove on the outside of the second part. The passage has an inlet for communication with a source of hydraulic fluid provided from, for example, an engine pump and an outlet that is in fluid communication with the check valve. The arrangement enables the check valve to be offset from the point where fluid is supplied to the tensioner thereby enabling the tensioner to be designed in a more compact configuration.