MGB Engine Manual p.80: Cylinder Head Refitting, Valve & Guide Replacement (A.7)
MGB engine procedure for refitting the cylinder head (FRONT/TOP gasket, 11-nut tightening order per Fig A.2) and removing/replacing valves and valve guides.
This is page 80 (section A, 'The Engine') of an MG B workshop/service manual, covering completion of cylinder head refitting and the beginning of Section A.7, 'Valve Gear and Valves'. The cylinder head refitting instructions note that the head gasket is marked 'FRONT' and 'TOP' (copper side up), and describe fitting the seven external head nuts finger tight, replacing push-rods in their original positions, tightening the 11 cylinder head nuts a turn at a time in the sequence of Fig. A.2, then tightening the four rocker assembly nuts, followed by warm-up and valve clearance checks. Section A.7 explains removing and replacing valves using valve spring compressor Service tool 18G45, keeping valves in order (exhaust heads are concave and smaller than inlets), fitting new synthetic rubber packing rings soaked in engine oil, and never reusing old packing rings. It also covers removing and replacing valve guides, specifying the dimensions of a hardened steel drift (9/16 in./14 mm diameter, at least 4 in. long, with a 5/16 in./7.9 mm spigot 1 in. long). Fig. A.4 shows the exploded valve assembly parts; Fig. A.5 shows valve grinding using Service tool 18G29.
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Frequently asked questions
- What order should the cylinder head nuts be tightened on this engine?
- Fit the seven external cylinder head nuts finger tight, then tighten the 11 cylinder head nuts a turn at a time in the order given in Fig. A.2, and finally tighten the four rocker assembly nuts.
- Which way does the cylinder head gasket fit?
- The gasket is marked 'FRONT' and 'TOP' to assist correct fitting, with the copper side uppermost.
- What tool is used to compress the valve springs?
- Service tool 18G45 is used to compress the double valve springs so the two valve cotters can be removed.
- Can old valve packing rings be reused?
- No. The manual notes that old valve packing rings must not be refitted or oil sealing may suffer; new rings fit more easily if soaked in clean engine oil for a short period before use.
- What size drift is needed to remove the valve guides?
- A hardened steel punch 9/16 in. (14 mm.) in diameter, not less than 4 in. (10 cm.) long, with a locating spigot 5/16 in. (7·9 mm.) diameter machined on one end for a length of 1 in. (2·5 cm.) to engage the guide bore.
- How can inlet and exhaust valves be told apart?
- The exhaust valve heads are concave and are smaller in diameter than the inlet valves.
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