MGB (Four Cylinder Versions)
Published: 8th Jun 2011 - 0 Comments - Be the first, contribute now!
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Featuring a conventional rear wheel drive set-up, plus BMC’s straightforward, uncomplicated overhead valve (pushrod) B-Series cast iron engine, in almost every respect the MGB is very easy to look after at home.
How easy is it to work on?
Featuring a conventional rear wheel drive set-up, plus BMC’s straightforward, uncomplicated overhead valve (pushrod) B-Series cast iron engine, in almost every respect the MGB is very easy to look after at home. An exception to this general statement is the distributor, which is positioned low down within the engine bay, and comparatively difficult to reach. As with any classic featuring twin carburettors, properly setting up the carburation is rather more time-consuming than in the case of a single carburettor vehicle. However, these are small moans in an otherwise rosy picture. Luckily all the components required are readily available from a variety of suppliers; most parts prices are reasonable.
Note 1: Mileage/time intervals shown here are suggested for typical use; frequency will need to be increased under harsh operating conditions.
Note 2: MGB specifications changed during production; please consult manufacturer’s literature for full details of each aspect of maintenance, specific to your version.
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.
Brakes
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. AVOID INHALING DUST FROM THE PADS/SHOES - IT MAY CONTAIN ASBESTOS. 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.
Engine
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). COMPRESSION PRESSURE AT CRANKING SPEED 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.
Ignition
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.
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.
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