A tracked work machine having an undercarriage assembly configured to drive the work machine over ground, the undercarriage assembly comprising: a drive wheel; a front idler wheel rotatable on a front axle, the front idler wheel defining a front idler axis; a rear idler wheel rotatable on a rear axle, the rear idler wheel defining a rear idler axis; an endless track belt disposed about the drive and idler (15, 16) wheels; a front track tensioner configured to position the front idler wheel to tension the track belt; a track roller frame pivotably mounted on the work machine with a main pivot defining a main pivot axis, the track roller frame comprising an elongate member with a front end and a rear end with the main pivot located between the front end and the rear end and the front idler wheel being connected near the front end of the track roller frame; a major bogie connected to the track roller frame, the major bogie comprising a forward bogie arm and a trailing bogie arm and pivotably connected to the track roller frame at a major bogie pivot defining a major bogie pivot axis; a swing link pivotably connected to the trailing bogie arm, wherein the rear idler wheel is mounted on the swing link; and a hydraulic cylinder connected between the rear end of the track roller frame and the swing link, the hydraulic cylinder configured to rotate the swing link to maintain desired tension in the track belt: characterised in that the undercarriage assembly further comprises a mechanical stop configured to interact with the swing link to limit the travel of the swing link when pressure is reduced in the hydraulic cylinder, wherein the mechanical stop is positioned on the trailing bogie arm and a toe on a lower end of the swing link contacts the mechanical stop, and wherein under normal conditions, track tension generated by the front track tensioner keeps the swing link in firm contact with the mechanical stop, and wherein when the front tensioner is retracted due to reverse torque from the drive wheel, the hydraulic cylinder rotates the swing link rearward to maintain desired tension in the track belt. a drive wheel; a front idler wheel rotatable on a front axle, the front idler wheel defining a front idler axis; a rear idler wheel rotatable on a rear axle, the rear idler wheel defining a rear idler axis; an endless track belt disposed about the drive and idler (15, 16) wheels; a front track tensioner configured to position the front idler wheel to tension the track belt; a track roller frame pivotably mounted on the work machine with a main pivot defining a main pivot axis, the track roller frame comprising an elongate member with a front end and a rear end with the main pivot located between the front end and the rear end and the front idler wheel being connected near the front end of the track roller frame; a major bogie connected to the track roller frame, the major bogie comprising a forward bogie arm and a trailing bogie arm and pivotably connected to the track roller frame at a major bogie pivot defining a major bogie pivot axis; a swing link pivotably connected to the trailing bogie arm, wherein the rear idler wheel is mounted on the swing link; and a hydraulic cylinder connected between the rear end of the track roller frame and the swing link, the hydraulic cylinder configured to rotate the swing link to maintain desired tension in the track belt: characterised in that the undercarriage assembly further comprises a mechanical stop configured to interact with the swing link to limit the travel of the swing link when pressure is reduced in the hydraulic cylinder, wherein the mechanical stop is positioned on the trailing bogie arm and a toe on a lower end of the swing link contacts the mechanical stop, and wherein under normal conditions, track tension generated by the front track tensioner keeps the swing link in firm contact with the mechanical stop, and wherein when the front tensioner is retracted due to reverse torque from the drive wheel, the hydraulic cylinder rotates the swing link rearward to maintain desired tension in the track belt.