Cam-lift for a manhole cover

1. A manhole cover assembly, comprising:

a frame defining an opening;

a cover sized to substantially cover the opening;

a lift pin mounted to the frame, the lift pin defining a first axis and including a bearing portion, the lift pin supporting the cover in an elevated position of the lift pin and being free to slide axially along the first axis relative to the frame;

a torque shaft journalled by the frame and defining a second axis offset from the first axis;

a spiral cam in rotary engagement with the torque shaft and including a cam surface in engagement with the bearing portion of the lift pin so that rotation of the torque shaft about the second axis causes rotation of the spiral cam about the second axis and displacement of the lift pin along the first axis.

2. The manhole cover assembly of claim 1 , wherein:

the frame includes a top flange and a bottom flange; and

wherein a pair of lift pin holes are formed through the top and bottom flanges coaxial with the first axis.

3. The manhole cover assembly of claim 2 , wherein at least one bushing is retained in the lift pin holes.

4. The manhole cover assembly of claim 2 , wherein:

the frame includes a housing; and

wherein a first hole sized to receive the torque shaft is formed through the housing coaxial with the second axis.

5. The manhole cover assembly of claim 4 , wherein:

the frame includes an interior land;

a second hole is formed through the interior land coaxial with the second axis to receive a lower end of the torque shaft; and

wherein a fastener engages the bottom end of the torque shaft, whereby the interior land is captured between the fastener and the torque shaft.

6. The manhole cover assembly of claim 1 , wherein the lift pin is fixed to the cover and the cover and lift pin are rotatable relative to the frame about the first axis.

7. The manhole cover assembly of claim 1 , wherein the bearing portion of the lift pin includes a recessed portion that bears on the cam surface.

8. The manhole cover assembly of claim 7 , wherein the cam surface of the spiral cam protrudes from the torque shaft.

9. The manhole cover assembly of claim 1 , wherein the torque shaft includes a bottom end having a threaded hole for receiving a fastener through an interior land defined by said frame.

10. The manhole cover assembly of claim 1 , wherein the spiral cam includes a polygonal opening therethrough sized to receive the torque shaft.

11. The manhole cover assembly of claim 1 , wherein the spiral cam includes a hexagonal opening therethrough sized to mate in driving engagement with the torque shaft.

12. The manhole cover assembly of claim 1 , wherein the torque shaft has a hexagonal cross-section.

13. The manhole cover assembly of claim 1 , wherein the cam surface of the spiral cam includes a notch sized to provide clearance for the lift pin when the spiral cam is in a predetermined orientation relative to the lift pin.

14. The manhole cover assembly of claim 1 , wherein the spiral cam includes a stop to limit the rotation of the spiral cam.

15. A method of uncovering a manhole frame, comprising:

engaging a wrench with a torque shaft journalled in the frame, the torque shaft being journalled in the frame along a generally vertical torque shaft axis;

turning the torque shaft with the wrench so as to turn a cam surface that is turned by turning the torque shaft about the torque shaft axis;

camming the cam surface along a surface of a lift pin by continuing to turn the torque shaft, resulting in lifting of the lift pin along a generally vertical lift pin axis that is laterally offset from the torque shaft axis;

the lift pin being connected to a cover sized to substantially cover an opening of the manhole frame so that lifting the lift pin lifts the cover; and

turning the cover about the lift pin so as to uncover the manhole frame.