MGB 1800 Engine rebuilding guide


Initial disassembly

1.      Drain oil and wash outside of engine

2.      Remove rocker box cover

3.      Loosen cylinder head nuts in sequence and remove

4.      Remove rocker shaft assembly

5.      Remove pushrods (keep in order)

6.      Remove head

7.      Remove cylinder head studs

8.      Remove water pump pulley

9.      Remove water pump

10. Remove alternator rear bracket

11. Remove oil filter extension and rubber seal

12. Remove engine mounts

13. Remove distributor drive

14. Remove tappet chest covers

15. Extract tappets

16. Remove oil cooler and oil pressure connectors

17. Remove oil pressure relief valve

18. Invert engine and remove sump

19. Remove oil pump

20. Knock back flywheel locktab and remove flywheel (chock crankshaft to prevent rotation)

21. Remove engine backplate

22. Knock back locktab and remove crank pulley (chock crankshaft to prevent rotation)

23. Remove timing chain cover

24. Knock back locktab and remove camshaft pulley nut

25. Remove oil thrower from crankshaft

26. Knock back locktab and remove timing chain tensioner

27. Pull off timing chain and sprockets

28. Remove camshaft thrust plate

29. Extract camshaft

30. Remove front engine plate

31. Note the numbers on the conrods and their respective cylinders

32. Undo conrod nuts and remove caps

33. Undo main bearing caps and remove

34. Lift out the crankshaft

35. Place engine on end and push out pistons and conrods


Unit disassembly



1.      Remove all studs

2.      Remove valve springs

3.      Remove valves


Rocker shaft

1.      Remove split pins

2.      Remove locking screw from rear post

3.      Remove all posts and rockers (keep in order)


Oil pump

1.      Remove filter mesh

2.      Remove drive gear

3.      Separate pump halves

4.      Remove rotors


Conrods & pistons

1.      Press out (or remove circlips, or undo pinch bolt) and remove gudgeon pins



1.      Wash out and clean all components

2.      Derust front and back engine plates

3.      Wire brush block and cylinder head

4.      Sand or bead blast all components



1.      Rebore block to next oversize or as required to achieve desired capacity

2.      Fit new valve guides as necessary

3.      Fit hardened exhaust seats and recut all seats

4.      Reface valves or replace as necessary

5.      Lap in valves to seats

6.      Regrind crankshaft to next undersize

7.      Replace and ream camshaft bearings as necessary

8.      Reface flywheel as necessary



1.      Invert engine

2.      Fit new main bearing shells and thrust washers to block

3.      Install crankshaft

4.      Fit new shells to main bearing caps

5.      Fit main bearing caps in block and nip up bolts

6.      Check crankshaft end float

7.      Remove caps and individually check bearing running clearances

8.      When clearances and end float are in limit, coat bearing surfaces with Graphogen and torque up the main bearing cap bolts

9.      Fit new pistons and gudgeon pins to conrods

10. Fit piston rings to pistons

11. Fit new big end shells to conrods and caps

12. Place engine on end

13. Insert pistons into cylinders

14. Invert engine

15. Check running and side clearances

16. When clearances are in limit, coat bearing surfaces with Graphogen and torque up the cap nuts

17. Coat camshaft with Graphogen and insert into block

18. Refit engine frontplate with new gasket

19. Refit camshaft thrust plate

20. Fit timing chain sprockets and check they are level - shim on crankshaft as necessary

21. Fit new timing chain to sprockets and fit to cam and crankshafts

22. Fit new timing chain tensioner and adjust

23. Degree the cam and adjust as necessary

24. Fit oil thrower to crankshaft

25. Fit new oil seal to timing chain cover

26. Refit cover with new gasket

27. Refit crankshaft pulley with new locktab

28. Refit engine backplate with new oil seal, gasket and locktab

29. Fit new rotors to oil pump ( or replace oil pump as necessary)

30. Refit pick up strainer to oil pump

31. Refit oil pump with new gasket

32. Refit sump with new gaskets and main bearing cap seals

33. Place engine right way up

34. Refit cylinder head studs

35. Fit valves to cylinder head using new valve springs

36. Fit head to block using new gasket

37. Coat new tappets with Graphogen and insert into block

38. Fit pushrods

39. Reassemble rocker shaft with new shaft, rebushed rockers and new split pins

40. Fit rocker shaft assembly to head

41. Torque up head nuts

42. Refit oil filter extension with new rubber seal

43. Refit oil cooler and pressure gauge connectors

44. Refit oil pressure relief valve

45. Refit distributor drive

46. Refit engine mounts

47. Refit flywheel with new locktab