MGB Workshop Manual p77 - Rocker Bushes & Cylinder Head Removal, Fig A.2 Sequence
MGB Workshop Manual engine procedure for removing the rocker shaft assembly and push-rods and refitting worn rocker bushes using service tool 18G 226.
This is page 77 of the MGB workshop manual ('THE ENGINE' section, page A.5, Issue 6, ref. 25729). It completes the rocker shaft assembly procedure (Section A.5), covering removal of the eight rocker shaft bracket nuts, withdrawal of the eight push-rods, dismantling the shaft, and reassembly notes including replacing the locating screw lock plate and checking the rocker cover cork gasket and cap nut rubber bushes. A subsection on refitting rocker bushes recommends Service tool 18G 226, describes positioning the bush butt joint and oil groove per Fig. A.3, and specifies drill sizes (.093 in./2.36 mm for the end plug oilway; No. 47 drill, .0785 in./1.98 mm for the top oil hole) and a replug rivet (Part No. 5C 2436). Fig. A.2 shows the cylinder head nut slackening and tightening sequence (positions 1–11). Fig. A.3 shows correct valve rocker bush position with oilways, bush joint, and oil groove labeled. Section A.6 begins the cylinder head assembly removal procedure: draining coolant (noting later 18GD and 18GG engines use a plug instead of a drain tap), removing the thermostat housing, air cleaners, carburetters, manifolds, rocker assembly, seven external head nuts, push-rods, HT cables, spark plugs, thermal transmitter, water pipe, and finally lifting the head evenly up the studs.
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Frequently asked questions
- What is the cylinder head nut slackening and tightening sequence on the MGB?
- Fig. A.2 on this page shows the sequence for the 11 cylinder head nuts, numbered 1 through 11 across the head (top row 9, 5, 1, 4, 8; bottom row 10, 6, 2, 3, 7, 11).
- What tool is recommended for replacing MGB rocker bushes?
- Service tool 18G 226 is recommended; the bushes and rockers can be easily damaged by using improvised drifts.
- What drill sizes are used when drilling rocker bush oil holes after fitting?
- Use a .093 in. (2.36 mm) drill to drill out the end plug and continue the oilway through the bush, and a No. 47 drill (.0785 in. / 1.98 mm) to continue the oil hole in the top of the rocker barrel through the bush. Replug the end with a rivet, Part No. 5C 2436, and weld the plug in position.
- How should a new rocker bush be positioned?
- Position the bush with the butt joint at the top of the rocker bore and the oil groove at the bottom of the rocker bore, as shown in Fig. A.3, then burnish-ream to the dimensions given in the 'GENERAL DATA' section.
- How do you begin removing the MGB cylinder head?
- Drain the cooling system (on later 18GD and 18GG engines the block drain tap is a removable plug and sealing washer), remove the top water hose, thermostat housing, air cleaners and carburetters, manifolds, rocker assembly and the seven external head nuts, push-rods, HT cables, spark plugs, thermal transmitter, and hoses; then break the head joint by levering at one end and withdraw the head evenly up the studs.
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