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A drilling motor assembly can include a housing, a shaft, and a pawl which selectively engages a recess, the pawl having an axis of rotation and a generally planar engagement face which engages a generally planar engagement face of the recess when relative rotation between the housing and the shaft

A drilling motor assembly can include a housing, a shaft, and a pawl which selectively engages a recess, the pawl having an axis of rotation and a generally planar engagement face which engages a generally planar engagement face of the recess when relative rotation between the housing and the shaft is prevented. The engaged engagement faces can be oblique relative to a radius extending from the axis of rotation to the engaged engagement faces. A method of drilling a wellbore can include flowing a fluid through a drilling motor assembly, thereby rotating a shaft relative to a housing, and rotating the housing, thereby engaging a pawl with a recess and preventing relative rotation between the housing and the shaft, the pawl and recess each having a generally planar engagement face, whereby the engaged engagement faces prevent relative rotation between the shaft and the housing.

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1. A drilling motor assembly, comprising: a housing;a mandrel comprising a recess;a pawl which selectively engages the recess, the pawl having an axis of rotation and a generally planar engagement face which is engagable with a generally planar engagement face of the recess, and wherein when the paw

1. A drilling motor assembly, comprising: a housing;a mandrel comprising a recess;a pawl which selectively engages the recess, the pawl having an axis of rotation and a generally planar engagement face which is engagable with a generally planar engagement face of the recess, and wherein when the pawl and the recess are engaged, the engagement faces are oriented at an oblique angle relative to a radius extending from the axis of rotation to the engaged pawl and recess engagement faces; andwherein the pawl is rotatable about a pivot pin received in an elongated opening such that the pivot pin is spaced from the housing along the elongated opening, whereby the pivot pin does not transmit torque between the housing and the mandrel when relative rotation between the housing and the mandrel is prevented. 2. The drilling motor assembly of claim 1, wherein the pawl and the recess are engagable such that relative rotation between the housing and the mandrel is permitted in one direction, but is prevented in an opposite direction. 3. The drilling motor assembly of claim 1, wherein a compressive force is transmitted between the housing and the mandrel via the pawl, without the compressive force being reacted by the pivot pin. 4. The drilling motor assembly of claim 1, wherein the pawl rotates with the housing, and wherein the recess rotates with the mandrel. 5. The drilling motor assembly of claim 1, wherein the pawl rotates out of engagement with the recess when relative rotation between the housing and the mandrel is permitted. 6. The drilling motor assembly of claim 1, wherein hydrodynamic pressure reduces contact pressure between the pawl and the recess when relative rotation between the housing and the mandrel is permitted. 7. The drilling motor assembly of claim 1, wherein the oblique angle is greater than 90 degrees relative to the radius and the engagement faces such that when the pawl and recess engagement faces are engaged, the pawl is prevented from disengaging from the recess. 8. The drilling motor assembly of claim 1, further comprising a turbine drilling motor which rotates the mandrel in response to fluid flow through the drilling motor. 9. The drilling motor assembly of claim 1, wherein predetermined mating surfaces of the drilling motor assembly are hardened to at least approximately 400 Brinell hardness. 10. A method of drilling a wellbore, comprising: flowing a drilling fluid through a drilling motor assembly, thereby rotating a mandrel relative to a housing; androtating the housing, thereby engaging a pawl with a recess in the mandrel and preventing relative rotation between the housing and the mandrel, the pawl and recess each having a generally planar engagement face, whereby the engaged engagement faces prevent relative rotation between the mandrel and the housing, wherein the pawl rotates about a pivot pin received in an elongated opening such that the pivot pin is spaced from the housing along the elongated opening and when a force is transmitted between the housing and the mandrel via the pawl, the force is not transmitted to the pivot pin. 11. The method of claim 10, wherein the pawl has an axis of rotation, and wherein the engaged pawl and recess engagement faces are oriented at an oblique angle relative to a radius extending from the axis of rotation to the engaged pawl and recess engagement faces. 12. The method of claim 11, wherein the oblique angle is greater than 90 degrees relative to the radius and the engagement faces such that when the pawl and recess engagement faces are engaged, the pawl is prevented from disengaging from the recess. 13. The method of claim 10, wherein relative rotation between the housing and the mandrel is permitted in one direction, but is prevented in an opposite direction due to the engaged pawl and recess engagement faces. 14. The method of claim 10, wherein the elongated opening is formed in the housing. 15. The method of claim 14, whereby the pivot pin does not transmit torque between the housing and the mandrel when relative rotation between the housing and the mandrel is prevented. 16. The method of claim 14, wherein the force is a compressive force transmitted between the housing and the mandrel via the pawl, without the compressive force being reacted by the pivot pin. 17. The method of claim 10, wherein the pawl rotates with the housing, and wherein the recess rotates with the mandrel. 18. The method of claim 10, wherein the pawl rotates out of engagement with the recess when relative rotation between the housing and the mandrel is permitted. 19. The method of claim 10, wherein hydrodynamic pressure reduces contact pressure between the pawl and the recess when relative rotation between the housing and the mandrel is permitted. 20. The method of claim 10, wherein the drilling motor comprises a turbine drilling motor. 21. The method of claim 10, further comprising hardening predetermined mating surfaces of the drilling motor assembly to at least approximately 400 Brinell hardness. 22. A drilling motor assembly, comprising: a drilling motor which rotates a mandrel relative to a housing in response to fluid flow through the drilling motor; anda pawl which selectively engages a recess in the mandrel to selectively prevent relative rotation between the mandrel and the housing, wherein the pawl is rotatable about a pivot pin received in an elongated opening such that the pivot pin is spaced from the housing along the elongated opening and when a compressive force is transmitted between the housing and the mandrel via the pawl, the compressive force is not transmitted to the pivot pin. 23. The drilling motor assembly of claim 22, wherein the elongated opening is formed in the housing, whereby the pivot pin does not transmit torque between the housing and the mandrel when relative rotation between the housing and the mandrel is prevented. 24. The drilling motor assembly of claim 22, wherein the pawl rotates with the housing, and wherein the recess rotates with the mandrel. 25. The drilling motor assembly of claim 22, wherein the pawl rotates out of engagement with the recess when relative rotation between the housing and the mandrel is permitted. 26. The drilling motor assembly of claim 22, wherein hydrodynamic pressure reduces contact pressure between the pawl and the recess when relative rotation between the housing and the mandrel is permitted. 27. The drilling motor assembly of claim 22, wherein the drilling motor comprises a turbine drilling motor. 28. The drilling motor assembly of claim 22, wherein the pawl has an axis of rotation about the pivot pin, and a generally planar engagement face which engages a generally planar engagement face of the recess when relative rotation between the housing and the mandrel is prevented, and wherein the engaged pawl and recess engagement faces are oriented at an oblique angle relative to a radius extending from the axis of rotation to the engaged pawl and recess engagement faces. 29. The drilling motor assembly of claim 28, wherein the pawl and the recess are engagable such that relative rotation between the housing and the mandrel is permitted in one direction, but is prevented in an opposite direction. 30. The drilling motor assembly of claim 28, wherein the oblique angle is greater than 90 degrees relative to the radius and the engagement faces of the pawl and recess such that when the pawl and recess engagement faces are engaged, the pawl is prevented from disengaging from the recess. 31. The drilling motor assembly of claim 22, wherein predetermined mating surfaces of the drilling motor assembly are hardened to at least approximately 400 Brinell hardness.