To remove existing parts:

1. Remove the PTO shaft from the machine.

2. Remove the upper and lower front guards.

3. Release and remove the drive chain jockey arm tension spring.

4. Slacken the chain tensioner bolt and remove the drive chain.

5. Unscrew the top two tensioner nuts, unscrew and remove the tensioner lower pivot bolt and nut. The tensioner can now be removed.

6. Unscrew and remove the gearbox pivot pin retaining bolt and nut.

7. Remove the gearbox pivot pin. The gearbox can now be removed.

8. Remove the split pin from the jockey arm pivot pin and remove the complete arm.

9. Clean off any excess oil or grease from within the gearbox compartment.

10. Using a gas cutting torch remove the existing gearbox front and rear mounting plates, the jockey arm pivot bush, tensioner adjuster bracket and tension spring hook links.

11. Clean up all cut surfaces with an angle grinder.

To fit new parts:

12. Place assembled new gearbox (OS1223-16) into the machine as shown in the drawings and align the two sprockets using a straight edge or plumb line. Tack weld in place.

13. In order to weld the rear mounting plate it will be necessary to temporarily remove the spline shaft and front flange. To do this, loosen the 2 grub screws on the rear spline shaft bearing. Open all 8 nuts around the housing flange and remove the spline shaft and front flange.

14. Stitch weld the rear mounting plate front and back. Fully weld the front mounting plate at the front and stitch weld it at the back.

15. Drill a 22mm hole for the drain bung as shown in the drawing.

16. Fully weld the M20 hex nut to the outside.

17. Drill a 17mm hole for the rear bearing grease tube as shown in the drawing.

18. Fully weld the grease tube block to the outside.

19. Position new chain tensioner assembly (OS1223-20) 10mm approx. above the gearbox assembly on the left side of the gearbox compartment.

20. Align with sprockets and tack weld in place.

21. Fully weld chain tensioner assembly.

22. Fit front baffle plate (OS1223-23) in place at an angle of approximately 20 degrees to the horizontal ensuring that the folded front face is flush with the front face of the side panels.

23. Fully weld the baffle plate.

24. Fit the front channel lip plate (OS1212-99) as shown in the drawing and fully weld.

25. Clean out any swarf or debris from around the gearbox compartment before replacing the spline shaft and front flange in reverse order to dismantling. Ensure that the gasket is positioned correctly.

26. Fit grease tube from right side panel to rear spline shaft bearing.

27. Fit M20 x 30 setscrew with dowty washer to drain bunghole.

28. Clean, prime and paint all modified parts (Keenan green). Allow paint to dry properly before continuing assembly.

29. Slacken chain tensioner bolt and threaded bar fully.

30. Fit new ASA100-drive chain and joiner link. It will probably be necessary to to cut the chain to the required length.

31. Adjust chain tensioner to give a maximum of 13mm inward movement in the center of the 2 sprockets (see operators manual).

32. Fill lower half of the gearbox chamber with universal type oil to a depth of approximately 90mm.

33. Fit the new upper front guard section with internal baffles (OS1212-85a).

34. Fit the new lower front guard section (OS1212-68a).

35. Fit a "540 RPM" sticker to the front guard lower section above the PTO shroud

36. Fit new T80 PTO shaft with 1 3/8" - 6 spline, shear bolt input and 1 3/4" - 6 spline, over-run clutch output.

37. Run machine and check that all parts are running smoothly.