Section A.26, Removing and Replacing the Camshaft
The Book gives explicit instructions to R&R the camshaft, but I do have a few additional observations. The camshaft can be removed without removing the oil pump drive gear, which means you don't need to remove the oil pan either. In fact the camshaft can be changed without removing the engine from the car, and without removing the cylinder head. See separate article on R&R of the Camshaft.

Section A.27, Refitting the Distributor Drive Gear
I have covered this part before, as there is some confusion about things like "large offset uppermost" and which rotation of the crankshaft is compression or exhaust. See separate article for Distributor drive gear alignment. Also be very careful, and do not drop the gear into the sump.

Section A.28, Removing and replacing the oil pump
This looks simple, and it is, with one additional warning. Engine gasket sets are commonly packaged with two oil pump gaskets, one for the 3-main-bearing engine and one for the 5-main-bearing engine. If you use the wrong gasket you could end up with no oil pressure, and having to R&R the sump and oil pump to change the oil pump gasket. The 5-main bearing MGB engine uses a different oil pump with an extra intake port on the top end that is not used in the MG engine. For the 5-main engine you MUST use the larger oil pump gasket to seal that extra port. Using the smaller gasket will allow air into the extra port in which case the oil pump will be trying to pump air and will not move any oil, resulting in no oil pressure.

Section A.29, Dismantling and Reassembling the oil pump
See separate article on Oil pump inspection which provides more information on inspection and testing of the oil pump to allow you to decide if it needs to be repaired or replaced, or if you can save some money and use the one you have.

Section A.30, Removing and Replacing the Flywheel
The rear plate, flywheel and clutch parts can be installed last, just before installation in the car. You may find it to advantage to install the rear plate before the oil pan, in the interest of getting the square cork seals properly installed on the front and rear main bearing caps. If you will be checking cam timing with a degree wheel, you may want to leave the timing cover and crank pulley off until that is finished. Before installing flywheel and clutch parts, check the spigot bushing in the tail end of the crankshaft. It is a cheap part and easy to replace, and you could end up kicking yourself later if you don't install a new one.

Section A.31, Removing and Replacing the Crankshaft
Starting with a bare engine block, install the crankshaft first, then the pistons. The con-rod bearing cap lock-tabs are easier to deal with if the camshaft is not in the way allowing (full rotation of the crankshaft with flat lock-tabs). Install oil pump and associated parts at your convenience, any time before the oil pan is installed. Install the engine front plate, camshaft (including tach drive gear), timing chain and associated parts (getting the cam timing right of course). Release tensioner spring, install tensioner plug. Install the CORRECT oil thrower ring before installing the timing cover with a new seal, followed by the crankshaft pulley.

Section A.32, Timing Chain Tensioner
Back in Section A.17 the text was dealing only with the timing chain, as very early production engines (158 cars) had no chain tensioner, and you cannot install a tensioner on those engines. Furthermore, the early cam sprocket with embedded rubber ring may not be available for replacement. Otherwise Section A.32 does a good job of detailing installation of the tensioner assembly (but my pictures can help).

Section A.33, Modified Gearbox Mounting Plate
Simple stuff, as long as the assembly is original. This is only about the oil drain groove which you should keep open, do not seal up. However, if your engine has a profuse oil leak at the rear, you may need to have the block and main bearing caps line bored, and might need to replace the crankshaft to renew the mechanical scroll seal parts. Line boring and crankshaft replacement is very expensive. You may consider alternately a modification to install a rubber rear seal.

Section A.34, Modified Tappets and Push-Rods
About 5400 cars into production the ball connection at bottom end of pushrods and top of tappets changed. This would only affect very early cars being different from later ones. If you have one of these early engines, watch out for a possible exchange of later parts in place of the early parts. The early parts may not be available for replacement, so if you need new tappets you may also have to buy new pushrods.

Section A.35, Piston Rings Changed
This is a simple change of parts in production, interchangeable for earlier cars. For most people this is a moot point, as they will commonly procure piston rings from the same source as new pistons. On the other hand, if you really want the chrome plated top rings (which I do), you may have to ask around and do some serious shopping to find them.

Section A.36, Modified Oil Filter
The change to various oil filter assemblies may be more complex than the simple note in Section A.36. Tecalemit and Purolator filter assemblies are not identical and require different bottom seals (among other things). The tough one is the early one-piece canister that has an odd rubber seal ring (hard to source) on the internal valve head. Many people will change the entire filter assembly to an aftermarket spin-on canister mount or an MGB spin-on canister mount, very convenient but not concours correct, and there are some possible pitfalls.

Section A.37, Modified Crankshaft
This item is detailing changes to the mechanical scoll seal at rear of engine block and crankshaft. In essence they opened up the running clearance and tightened up the tolerances to avoid mechanical contact of the iron parts if the main bearings become worn. This is a very common problem area on old cars with old engines, as many of them have had badly worn bearings in a past life. As a result, many of them have damaged scroll seal parts that are difficult AND expensive to repair (see Line Boring). This is when some people (including myself at one time) may opt for a less expensive and more expedient modification to install a rubber rear seal.

Section A.38, Modified Pistons and Gudgeon Pin
See Confidential Service Memorandum MG229. The ID of the wrist pin was reduced to the size of a wooden pencil. The key point here is, the newer parts are stronger, and all replacement parts "should" be the newer type, so don't go out of your way looking for the earlier type parts just to be original. No concours judge is ever going to see wrist pins. The later type parts are also heavier, so they must be fitted in matched sets for reason of engine balancing. Also don't be particularly surprised if a new set of aftermarket pistons has wrist pins with larger ID. You can take that issue up with the parts supplier.

Section A.39, Modified Oil Pump and Strainer
This is one of my pet issues, as the early style oil pump and sump strained bit me for a very expensive repair (more than once) before I figured this out. By all means, do change an early style oil pump and strainer to the later type at earliest convenience.

Section A.40, Fitting Flywheel Starter Ring
I have additional instructions for this procedure. Check that link and a few more pages to follow. (Back yard barbeque, anyone?)

Section A.41, Fitting Valve Seat Inserts
First word of warning is, this is a precision machining procedure that is beyond the facilities and tools of most car owners. If you happen to have a milling machine with a boring head and know how to use it, then the specifications in the Book will help you do it right. Otherwise expect to pay the machine shop to install and machine new valve seats.

Section A.42, Fitting Cylinder Liners
If you think my last word was harsh, don't try this at home. This requires a long reach boring head and the finesse of an experienced machinist. Tolerance on the machined bore is total range of 0.0005-in (0.0127-mm). Tolerance on OD of the liner before installation is 0.00075-in (0.0190-mm). The parts have an interference fit that requires a press and a piloted punch to push the liner into place (or to remove an older liner).

Section A.43, Modified Pistons and Rings
This is another possible moot point. If you are installing new pistons the proper rings will usually be included, especially if the pistons are not as original spec. This issue of ring groove size is important if you intend to source new rings to fit on old pistons.

Section A.44, Modified Power Unit
This is more about the later high starter position and flanged output shaft on the gearbox. It says the later parts are not interchangeable with earlier parts, but by now we should all know where there's a will there's a way. Mixing and matching of earlier and later parts has been endemic when these cars were not worth so much as they are today. Now many more people are interested to returning the cars to original style, while there are still plenty of hot-rodders playing mechanical tricks. So before you buy parts, check closely to see what parts are actually in your car, as it may not be original.

Section A.45, Oil Cooler Kits
Original style optional oil coolers had steel oil pipes from the inner fender (inner wing) to bottom of the cooler radiator, and short rubber hoses from the pipes to the engine. Those parts are once again available if you ask around and pay the price. Otherwise top entry oil coolers and long hoses are common aftermarket parts.

Section AA.1, Piston Sizes and Cylinder Bores
The point here is that in mass production the cylinder bore size was allowed to vary slightly, such that pistons of slightly different size were selected to match the bores. Numbers were stamped on top of the block and on top of the pistons to designate the variation of actual bore size. By far the most common number is "2" in a diamond, which seems to denote standard size. If it is something different, then all cylinders should have the same number stamp. When the bores were not closely matched, the factory would re-hone the smaller bores to match the larger bores so they would all use the same size pistons.

All of this is a moot point on a well used engine. For re-boring and installing new pistons, the new pistons are generally a matched set that will fit a standard bore size as interchangeable parts. Otherwise a machine shop will do precision boring to make the cylinders fit the new pistons. I think this is actually the "exception to the rule". In practice it is common to re-bore an engine as much as is required to clean up the cylinders, finishing at a consistent precision standard overbore size, and then buy standard precision oversize pistons to match. The end result is indeed interchangeable parts like the original production line never endeavored to achieve. So once your engine block is re-bored and you have new matching pistons in hand, you can drop any piston into any bore, and nobody needs to mark the block. Replacement pistons will normally have the overbore size marked on top. Top of the block may retain the original numbers in diamond markings. If the block is ever "decked" to make it flat again those marks may vanish, which is a good clue that the deck has been machined down (and watch out for piston to head interference).

Having passed all of the Book sections, there is some additional information for engine rebuilding.

Once the camshaft and timing parts are installed you get back to the top end. Grease the cam lobes generously, and also the bottom end of the tappets. Place tappets back in original bores if re-using original cam and tappets. If you mix up the old tappets they will be trash, and you get to buy a new set. You can install new tappets on an old cam, but never use old tappets with a new cam. Oil the sides of the tappets and drop them into the bores to set firmly on the cam lobes. Install a new head gasket and set the cylinder head in place. Install the pushrods and the rocker arm assembly. If the rocker arms are in place on the head first, you may want to install the front and rear pushrods before dropping the head into place.

Torque cylinder head bolts by the book, and adjust rocker clearance as specified. Once the engine is back in the car, reinstall manifolds, carbs, exhaust system, and other peripheral equipment. Fill with proper fluids and crank it up. Initial bedding in of a new cam or new tappets requires 20 minutes running at 2500 rpm. If you need to shut it down during this run you can resume later running 2500 rpm for the balance of the required 20 minutes. Re-torque cylinder head and re-adjust rockers after initial warm up. After 300 to 500 miles change oil and filter and re-torque the head again for good measure.