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MGB (All Four-Cylinder Versions)

Published: 5th Apr 2011 - 0 Comments - Be the first, contribute now!

MGB (All Four-Cylinder Versions)
MGB (All Four-Cylinder Versions)
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Front wheel bearings: Every 12,000 miles, re-lubricate the bearings with grease specifically stated as being suitable for wheel bearing use.


Overhead valve (pushrod), in-line four-cylinder BMC B-Series 1798cc, 98bhp

Valve Clearances

Inlet and exhaust, 0.015in. (cold). Adjustment is by conventional screw and locknut. Use the handy ‘Rule of 9’; check/adjust valve No. 1 with No. 8 fully open, No. 2 with 7 open, No. 3 with 6 open, and so on (each case sum of valve numbers is 9).


8.0:1 compression ratio, approx. 130 p.s.i.
8.8:1 compression ratio, approx. 160 p.s.i.
9.0:1 compression ratio, approx. 170 p.s.i.


Firing order: 1-3-4-2 (No. 1 cylinder at front of engine)

Spark plugs: Champion N9Y or equivalent. Gap 0.024in. to 0.026in. Every 6000 miles or annually (whichever comes first), check and clean the plugs; renew regardless every 12,000 miles.

Contact points: Gap 0.014 to 0.016in. corresponding with dwell angle reading of 60 +/- 3 degrees (Lucas 25D4 distributor), or 51 +/- 5 degrees (later examples with Lucas 45D4 distributor)

Every 3000 miles or annually (whichever comes first):

Check and clean the contact points (renew points regardless every 6000 miles).

Clean and check distributor cap, rotor arm and high tension leads; ensure that all connections are sound.

Distributor - mechanical aspects: Remove the rotor arm and apply a few drops of engine oil to the moving contact pivot, distributor shaft/cam bearing and mechanical advance mechanism (through apertures in the distributor’s baseplate).

Apply a little grease to the distributor’s cam to prevent rapid point ‘heel’ wear.

Timing: Check/re-set, referring to the pointer on the timing case and the crankshaft pulley notch. Note – Timing settings varied according to specific version. A wide variety of settings were specified; please consult the manufacturer’s literature relevant to your vehicle for recommended settings. The following figures should be regarded as starting points. Note that many MGBs have had replacement distributors installed over the years.

Before checking the dynamic (strobe) timing, disconnect the vacuum pipe from the distributor, and plug the pipe (remember to unplug the pipe and reconnect it on completion).

Engine prefix 18G, also 18V584Z, 18V585Z, 18V672Z and 18V673Z:

Static settings: High compression, 10 degrees BTDC; low compression, 8 degrees BTDC.

Dynamic (strobe) settings: High compression, 14 degrees BTDC @ 600 rpm; low compression, 12 degrees BTDC @ 600 rpm.

Engine prefix 18V581F, 18V582F, 18V583F, 18V581Y, 18V582Y, 18V583Y:

Static settings: High and low compression, 10 degrees BTDC.

Dynamic (strobe) settings: High and low compression, 13 degrees BTDC @ 600 rpm.

Engine prefix 18V:

Static setting: High compression, 5 degrees BTDC.

Dynamic (strobe) setting: High compression, 15 degrees BTDC @ 1000 rpm.

Engine prefix 18V779F, 18V780F:

Static setting: High compression, 6 degrees BTDC.

Dynamic (strobe) setting: High compression, 11 degrees BTDC @ 1000 rpm.

Engine prefix 18V846F, 18V847F, 18V797AE, 18V798AE, 18V801AE (CC), 18V802AE(CC), 18V883AE (CC), 18V884AE (CC), 18V890AE (CC), 18V891AE (CC), 18V892AE, 18V893AE:

Static setting: 7 degrees BTDC.

Dynamic (strobe) setting: 18V846F, 18V847F, 10 degrees BTDC @ 1000 rpm, 18V797AE, 18V798AE, 18V892AE, 18V893AE, 13 degrees BTDC @ 1500 rpm. 18V801AE (CC), 18V802AE(CC), 18V883AE (CC), 18V884AE (CC), 18V890AE (CC), 18V891AE (CC), 10 degrees BTDC @ 1500 rpm.


At least every 3000 miles or annually, whichever comes first: Examine the front brake pads and discs, also the rear shoes, cylinders and drums (remove the drums for a complete check). Scrutinise also the brake pipes, flexible hoses and master cylinder.

Renew any ailing components at once.


Adjust the brake shoe to drum clearances as required (rotate the adjusters on the backplates clockwise until the brakes are locked, pump the brake pedal to centralise the shoes, then back off the adjustment until the wheel rotates without binding). Next, assess handbrake operation and re-adjust the cable length if necessary (at the lower end of the handbrake lever, below the floor). After adjustment, check that the handbrake is fully ‘on’ with the lever applied by approximately four or five ‘clicks’ of travel, and then ensure that the brakes are not binding with the lever in the ‘off’ position.

At least every two years, renew the brake fluid after flushing out the system.


Engine oil: Every 3000 miles or annually (whichever comes first):

Change the oil and filter. Use high quality, SAE15W50, 20W50 or 20W60 oil. Please dispose of the old oil in an environmentally friendly manner - local councils provide waste oil collection points.

Sump capacity, including oil cooler: Approx. 7.5 pints (4.26 litres)

Manual Gearbox oil: Every 3000 miles/annually (whichever comes first), check/top up the gearbox (with the car horizontal).

Note: Early cars have a gearbox dipstick, reached from inside the car, after removing a rubber plug in the transmission casing. Later examples have a screw-in filler/level plug, reached from under the car. Remove the plug and check that the oil is up to the base of the threads in the filler plug aperture.

Every 24,000 miles (approximately), drain the gearbox (after a long run, when the oil is fully warm), then re-fill with fresh lubricant, to the same specification as that used in the engine.

Gearbox capacity: Early cars, approx 4.5 pints (2.56 litres); later cars, approx. 5.25 pints (2.98 litres). In each case if overdrive is fitted, add approx. 0.75 pints (0.43 litres).

Automatic transmission fluid: Check the fluid level with the engine at normal operating temperature and idling, with the transmission control lever in ‘Park’. The fluid should be up to the ‘Max’ marking on the dipstick. Use automatic transmission fluid Type F; capacity approx. 10.5 pints (5.97 litres).

Rear axle oil: Approximately every 24,000 miles/annually (whichever comes first), remove the filler/level plug and ensure that the lubricant is up to the base of the threads in the plug aperture.

Approximately every 12,000 miles, drain the axle oil after a long run, and re-fill with fresh lubricant.

Use SAE90EP hypoid oil; capacity approx. 2.25 pints (1.28 litres) for early cars with ‘banjo’ type axle; approx. 1.5 pints (0.85 litres) for later examples.

Running gear: At least every 1000 miles, re-lubricate the front suspension and propeller shaft (use lithium-based, multi-purpose grease).

Attend to these grease nipples:

King pins (nipple at top and bottom on each side); note that some cars have an additional nipple just above the lower fulcrum pin.

Propeller shaft: Early cars originally had a nipple on each universal joint (although the joints may have been replaced with ‘sealed for life’ types); all have a greasepoint on the sliding splines at the front of the shaft.

Handbrake mechanical linkage: Apply fresh grease via the nipple in the cable’s outer casing. Ensure that all pivot points are properly lubricated, and that they move freely.

Front wheel bearings: Every 12,000 miles, re-lubricate the bearings with grease specifically stated as being suitable for wheel bearing use.

Wire wheel splines: On cars fitted with wire wheels, whenever the wheels are removed, ensure that the hub splines are coated with copper-based, anti-seize compound (alternatively, use grease), to prevent seizure of the wheels on the splines. Check specifically to ensure that the splines are not worn (indicated by sharply pointed profiles); this is potentially EXTREMELY dangerous as the brakes may be rendered inoperative if the splines are not in good condition. Renew all worn components.

Other aspects:

Every 3000 miles, lubricate the carburettor pivot points/controls, also the accelerator pedal pivot.

Every 3000 miles, lubricate the hinges and lock mechanisms (wipe off excess lubricant).

Every 3000 miles, lubricate the clutch and brake pedal pivot points (take care lubricant doesn’t get on pedal rubbers).

Every 12,000 miles, re-oil the dynamo rear bearing (using a few drops of engine oil), and - where provision is provided for relubrication - re-grease the water pump (use special water pump grease).

Fuel System

Every 3000 miles or annually (whichever comes first):

Examine all fuel system pipework and check/top up the carburettor dashpots with SAE 20 oil. Examine/clean the filter in the SU electric fuel pump.

After the valve clearances and all ignition settings have been checked/set, and with the engine fully warmed up, check/re-set the carburettor mixture/throttle stop settings (use proprietary equipment for precisely balancing the carburettors). Aim for an idling speed of approximately 500 rpm with 18G engines, or 750 to 850 rpm for 18V versions. (Important Note: If the fuel mixture seems excessively rich after all engine/carburettor adjustments have been made, the carburettor needles and jet assemblies may be worn. Renewing ailing needle/jet will improve emissions and fuel consumption, and transform ‘driveability’).

Every 6000 miles, check air filter elements and renew if visibly obstructed (renew regardless every 12,000 miles). At each service, ensure that the breather pipework is unobstructed.

Cooling System

At all times, use top quality anti-freeze mixture containing corrosion inhibitors.

Every 3000 miles/annually, check the radiator, all hoses, the water pump and the fan.

At least every three years, drain the system, extricate the thermostat and reverse-flush the system prior to re-filling with fresh anti-freeze solution (observe the dilution recommendations of the anti-freeze manufacturer – these are printed on the container).

Capacity, including heater: Approx. 10 pints (5.68 litres) on cars up to Car Number 410002; 12 pints (6.82 litres) on later vehicles.

Sundry Items

Every 3000 miles, or annually (whichever comes first):

Check the fan belt and re-tension if necessary (3/4 in. deflection at the centre of the belt run between the crankshaft and dynamo pulleys, or 1/2 in. at the centre of the run between the crankshaft and alternator pulleys).

Examine the clutch operating system hydraulics for deterioration/leaks.

Assess the cleanliness/security of all electrical connections; inspect all wiring for damage.

Scrutinise the steering rack gaiters for splits/leaks. If damaged, the gaiters should be replaced at once, to prevent dirt and moisture from entering the rack. Re-lubricate the rack after fitting new gaiter(s); use SAE 90EP oil; total capacity approx. 0.33 pints (0.19 litres).

Check the security of the steering column clamp bolt.

Assess the condition/security of all running gear components and suspension mounting bushes.

Inspect the entire underbody for damage, and rectify paint blemishes.

Every 12,000 miles, fit a new oil filler cap/filter assembly.

Every 12,000 miles (on later models), check/clean the crankcase breather.

Every 12,000 miles, check engine compression readings.

Every 12,000 miles, assess wear in the hub bearings.

Every 12,000 miles, examine the springs for damage and shock absorbers for deterioration/leaks.

Best Mods

  • Where do you start and end with an MGB? There’s so much you can do given the budget but the most cost effective upgrade is a thorough service and tune up!
  • Converting to modern telescopic dampers is a costly but effective tweak even if they make the ride a lot firmer. If funds allow, the complete front end of the MGB RV8 is best plus it means modern brakes too.
  • Remember, 1977-onwards rubber bumper cars had front/rear anti roll bars fitted, which may cut down roll but only earlier raised spring set up. Beware, this low cost mod may lead to car becoming too twitchy with standard spec suspensions (speak to a specialist) n The inherent heavy and strong self-centering steering action is due to excessive castor angles, dialled in when the MG ran on crossply tyres. Kits are available to change this and it makes the car much easier to drive.
  • The B-Series is very tuneable and there’s lots of mods around; better breathing (gas flowed head, rejetted carbs and tuned exhaust manifold) is the first step. The engine can even be stretched to 2.1-litres.
  • Overdrive works well but fitting Ford Sierra transmission (typically £1500 as a kit) is more user friendly plus has superior ‘intermediates’ to compensate for nasty second/third gap found on standard transmissions.

Top Tips

  • The front suspension requires regular lubrication to keep the swivels in good order but surprisingly few do it properly. It should be done with the weight off the car, making sure to push all the old lube out. Speak to a specialist for advice on the best lubricant to use (some experts vary on their choice).
  • Lever arm dampers are fairly prone to losing their performance early, especially cheap recon units. Although only a short term solution, on types that can be refilled (or even re-valved), you can substitute old oil with thicker stuff to renew their effectiveness; ‘bounce’ on car’s corners to push old oil out first.
  • Tappety engines are a way of B-Series engine life, which is usually caused by a worn rocker shaft rather than the cam followers (lower down in engine).
  • Oil leak at the front of the engine near the thermostat housing? Looks odd but yes, it is coming from there! The remedy is to remove and clean the area, using joining sealant upon reassembly.
  • Transmissions can be noisy but soldier on regardless. On overdrives, if it’s reluctant to work, check the oil level rather than look for electrical fault first of all.
  • Noisy rear suspension? It’s not unknown for the half elliptic rear springs to chatter away caused by slackening clamps. Check them.
  • If using second-hand suspension components, bear in mind that the GT ran on stiffer springs, so buy in sets to avoid a mis-match.
  • Rear mounted battery location means power drop to the starter, especially if the connections are old and tired. Check and makes sure they are A1, especially the earths and consider renewing with heavier duty cable.
  • MGB heaters won’t burn you! And after the coldest snap for 13 years you can improve yours by renewing the thermostat and fitting a 88 Centigrade type. The engine is rather over-fanned; ditch it for electric one.
  • Engine and gearbox mountings can wear/fail quickly leading to strange engine knocking (unit can rock excessively on start up) and lead to clutch judder.

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