Throughout the years of production from May 1962 to Oct 1980 the MGB went through a number of changes and modifications brought about by general upgrades and improvements in safety & use regulations.  The main specifications and changes are shown below.
MGB Tourer and MGB GT - produced from May 1962 to Nov 1967 (GT from Sep 1965). Roadster; GHN3, GT; GHD3.
 
Production of the first MGB Tourer (also known as a Roadster) on 22 May 1962 and MGBGT production started in Sep 1965.
Engines:
Variants: 18G - May 1962 to Feb 1964, 18GA - Feb 1964 to Oct 1964, 18GB - Oct 1964 to Nov 1967.
The 18G and 18GA engines are fitted with a 3 bearing crankshaft and from 18GB onwards the engines are all fitted with a 5 bearing crankshaft.
4 cylinder 80.26 x 88.9mm, 1798cc, 2 x 1½in HS4 SU Carbs, 95bhp (net) at 5,400rpm. Maximum torque 110lbs. ft. at 3,000rpm.
Compression ratio:  as per engine number prefix, H (high compression) 8.8:1, L (low compression) 8:1.
Electrical
System:
From May 1962 to Nov 1967 - Positive earth electrical system with two six-volt batteries connected in series to give twelve volts output.  The batteries are located behind the driver's and passenger's seats under an access panel in the floor over the rear axle.
Transmission:
Axle ratio 3.909:1. Overall gear ratios 3.909:1 (overdrive 3.14:1), 5.369:1 (overdrive 4.31:1), 8.656:1, 14.214:1, reverse 18.588:1. Gearbox with synchromesh on 2nd 3rd and 4th gears only.  Optional Laycock de Normanville D Type overdrive with a ratio 0.802:1 from January 1963. 17.9mph/1,000rpm in top gear, 22.3mph/1,000rpm in overdrive.
Suspension and Brakes:
Independent front suspension (IFS), coil springs, wishbones, Anti-roll bar (optional on tourer until Chassis No 108039), live rear axle, half-elliptic leaf springs, lever-arm dampers. 10.75in. front disc brakes, 10 x 1.75in. rear drums. 4.0in. rims (Tourer disc), 4.5in. rims (centre-lock wire) or 5.0in. rims (GT disc).
Rear Axle:
Roadster - Hypoid three-quarter-floating (Banjo) rear axle from May 1962 to Jul 1967 and Hypoid semi-floating (tube-type Salisbury) axle from Jul 1967 to Nov 1967.
GT - Hypoid semi-floating (tube type Salisbury) rear axle from model introduction in Sep 1965 to Nov 1967.
Both rear axles have a 3.909:1 ratio.
Wheels:
Roadster – steel disc wheels 4Jx14 with 12 oval ventilation holes were fitted as standard.  GT - similar steel disc wheels enlarged to 5Jx14.  Plain hub caps were fitted.  As an alternative 60 spoke centre lock spoked (wire) wheels 4.5Jx14 were available for both Roadster and GT painted in silver-grey.  These were secured by 2 ear spinners.  Octagonal spinners were used where 2 ear spinners were illegal.  Spinners were ‘handed’.  Those on the right side of the car had a left hand thread and spinners on the left side had a right hand thread.  This ensures that the spinner is always turned towards the rear of the car when tightened.  From Feb 1964 thread pitch was changed from 12 TPI to 8 TPI.  Spinners were plain but annotated with an ‘undo arrow’.  Tyres were fitted with tubes.
Steering:
Rack and pinion steering.  Turning circle:  32ft.  Turns lock to lock:  2.93. Castor angle:  nominal 7º (unladen)  Camber angle:  nominal 1º positive.  Kingpin inclination:  nominal 8º. Toe-in:  1/16 to 3/32in (1.5 to 2.3mm)(unladen).
Dimensions:
Wheelbase 7ft 7in; front track 4ft 1in; rear track 4ft 1.25in. Length 12ft 9.3in; width 4ft 11.7in; height (Tourer) 4ft 1.4in, (GT) 4ft 1.75in. Unladen weight 2,030lb. (Tourer), 2190lb. (GT).
Exterior Door Handles:
From April 1965 Body 57986 - change from 'pull' type exterior door handles to the 'push-button' type handles when anti-burst door locks were introduced.
Performance:
Top speed:                105 mph.
0 - 60 mph:                Roadster 12 seconds;    GT 13.5 seconds.
Fuel consumption:     22 - 28 mpg.
MGB Mk II Tourer and GT - produced from Nov 1967 to Aug 1971.
Roadster; GHN4, GT; GHD4 to Sep/Oct 69 then Roadster; GHN5, GT; GHD5 from there to Aug 1971.


Specification as for Mk I MGB models except for:
Engines:
Variants: 18GD - Nov 1967 to Oct 1968 for home market cars, 18GF - Nov 1967 to Oct 1968 for North American cars.  18GG - Oct 1968 to Aug 1971 home market, 18GH - Oct 1968 to Aug 1970 North America, 18GJ - Oct 1969 to Aug 1970 California cars, 18GK - Aug 1970 to Aug 1971 North America.
(Federal markets) 1971 model-year, 2 HIF4 SU carbs, 82bhp (DIN) at 5,400rpm. Maximum torque 97lb ft. at 2,900rpm.  Home market cars continued to use the HS4 carbs.
Compression ratio:  as per engine number prefix, H (high compression) 8.8:1, L (low compression) 8:1.
Electrical
System:
From Nov 1967 to Aug 1971 - Negative earth electrical system with two six-volt batteries connected in series to give twelve volts output.
Transmission:
From Nov 1967 new gearbox with all-synchromesh gears.  Axle ration 3.909:1, overall ratios 3.909:1 (overdrive 3.2:1), 5.4:1 (overdrive 4.43:1), 8.47:1, 13.45:1, reverse 12.098:1.  Optional Laycock Type LH overdrive introduced with ratio of 3.14 .  From 1970 model-year (Sep/Oct 69) wheels 4.5in. rims, Rostyle sculptured steel pattern or optional centre-lock spoked (wire) wheels as before.
Borg-Warner Type 35 three speed epicyclic automatic gearbox offered as an optional extra from Nov 1967 with overall ratios 3.909:1, 5.668:1, 9.34:1, reverse 8.17:1.
Rear Axle:
Roadster and GT - Hypoid semi-floating (tube-type Salisbury) rear axle with 3.909:1 ratio from Nov 1967 to Aug 1971.
Wheels:
On introduction of the Mk II models options remained as above except that octagonal spinners were fitted to all export cars and introduced in the home market from Aug 1968.  From 1970 model-year (Sep/Oct 69) Rostyle sculptured 4.5Jx14 steel wheels were introduced.  Spoked (wire) wheels remained on option as before.
Steering:
As above.
Dimensions:
As above but with unladen weight 2,140lb. (Tourer), 2,260lb. (GT).
Performance:
Top speed:                 Roadster 107 mph        GT 104 mph.
0 - 60 mph:                Roadster 11 seconds    GT 14 seconds.
Fuel consumption:     22 - 28 mpg.
MGB Mk III Tourer and MGB GT - produced from Aug 1971 to Oct 1980.
1972 model-year (Aug 71) to 1974 model-year (Aug 73) inclusive, specification as for MGB Mk II except for:

155-14 (Tourer), 165-14 (GT) radial-ply tyres standardized on British market from start of 1973 model-year (Aug 72): all markets 1974 model-year (Aug 73).   Brake vacuum-servo standardized (British market) from start of 1974 model-year (Aug 73).
Sep 1974 start of Rubber bumper production.
Dec 1974 MGB GT no longer available in North America.
1975 model-year (Dec 74) and 1976 model-year (Sep 75) inclusive, specification as for Mk II and earlier Mk III models.
Engines:
Variants: 18V - Aug 1971 to Oct 1980.  There were an number of variations of this engine depending on carburation and emission controls.
British models now have a recalibrated power output of 84bhp (DIN) at 5,250rpm. Maximum torque 104lb. ft. at 2,500rpm.  HIF4 carbs were introduce on the home market cars from Nov 1973.
Federal models: Zenith-Stromberg carburettor. 65bhp (DIN) at 4,600rpm. Maximum torque 92lb. ft. at 2,500rpm.  Overall gear ratios unchanged except optional overdrive 3.21. 21.8mph/1,000rpm in overdrive.
The Zenith-Stromberg carb was introduced in Dec 1974.
Compression ratio:  as per engine number prefix, H (high compression) 9:1, L (low compression) 8:1.
Transmission:
Optional automatic gearbox discontinued in Aug 1973.
Rear Axle:
Roadster and GT - Hypoid semi-floating (tube-type Salisbury) rear axle with 3.909:1 ratio from Aug 1971 to Oct 1980.
Wheels:
Rostyle wheels with optional spoked (wire) wheels remained in use to the end of MGB production.  In 1975 V8 style alloy wheels painted gold were fitted to the Jubilee special edition model and LE alloy wheels were an option on home market cars in 1979 and 1980.
Electrical
System:
From Aug 1971 to Sep 1974 - Negative earth electrical system with two six-volt batteries connected in series to give twelve volts output.  From Sep 1974 on with the introduction of the 'rubber bumper' cars this was changed to a single twelve volt battery.
Steering:
As above.
Dimensions:
Overall length 13ft 2.25in; height 4ft 2.9in.  Otherwise as above.  Unladen weight not affected.
From the start of 1977 model-year, specification as for earlier MGB models except for:
Suspension:
Front and rear anti-roll bars now standard.
Dimensions:
Unladen weight 2,253lb. (Tourer) 2,260lb. (GT).
Performance:
Top speed:                 Roadster 107 mph        GT 104 mph.
0 - 60 mph:                Roadster 11 seconds    GT 14 seconds.
Fuel consumption:     22 - 28 mpg.
MGB production ceased on 23 October 1980.
Service/Maintenance
Tyres:
Up to 1972:  5.60-14 cross ply tyres were fitted as standard - normal or whitewall versions.
1965 on:  155-14 (Roadster), 165-14 (GT) radial tyres were optional.
In 1975 GT Jubilee models with the V8 style wheels were fitted with 175HR-14 tyres.
From the start of rubber bumper production in 1974 tubeless 165SR-14 tyres were fitted to both Roadsters and GTs. North American cars had tubes until 1976.
Inner tubes may be required for cars with spoked (wire) wheels.  Some new wire wheels can be tubeless so check with the manufacturer.
Road wheel nuts:  60 to 65 lb. ft. (8.3 to 9 kg. m.).
Tyre Pressures:
5.60-14 cross ply:  Front 19lb./sq. in. (1.34kg./cm.²) Rear 22lb./sq. in. (1.55kg./cm.²).
Radial-ply tyres:  Front 21lb./sq. in. (1.48kg./cm.²) Rear 24lb./sq. in. (1.69kg./cm.²)
For competition work and sustained high speeds:  Front 23lb./sq. in. (1.62kg./cm.²) Rear 26lb./sq. in. (1.83kg./cm.²)

Ignition:
Contact breaker gap:  0.014-0.016in (0.35-0.40mm).
Spark plug type:  Champion N9Y (or equivalent for other manufacturers).
Spark plug gap:  Up to 1976 - 0.025in. (0.64mm.), 1976 on - 0.035in. (0.89mm.).
Dwell angle:  Up to 1974 with Lucas 25D4 distributor - 60° ±3°.3°, 1974 on with Lucas 45D4 distributor 51° ± 5°.
Timing:
Pointer on timing case, notch on crankshaft pulley.  Consult workshop manual, timing varies depending on engine version.
Valve Rocker Clearance:
Valve rocker clearance 0.015in. (0.38 mm.) set when cold.
Capacities
Fuel Tank:
Up to March 1965 - 10 Imp gallons (12 US gallons, 45 litres).
March 1965 on - 12.7 Imp gallons (14 US gallons, 58 litres).
On North American cars fitted with the evaporative loss system the capacity was effectively reduced to 10 Imp gallons (12 US gallons).  This was from Oct 1969 in California and from Aug 1970 for all North American cars.
Lubricant:
Selecting the correct type of oil is important.  Modern synthetic oils are not suitable for these older engines.  A good quality classic oil should be used of which there are a number of manufactures in the market.
Engine:  7.5 Imp pints (9 US pints, 4.26 litres) 20/50 multigrade.
Oil pressure idle: 10 - 25 lb. sq. in, normal: 50 - 80 lb. sq. in for all models.
Gearbox (3 synchro):  4.5 Imp pints (5.6 US pints, 2.56 litres) 20/50 multigrade.
Gearbox with overdrive (3 synchro):  5.5 Imp pints (6 US pints, 3.36 litres) 20/50 multigrade.
Gearbox (4 synchro):  5.25 Imp pints (6 US pints, 3 litres) 20/50 multigrade.
Gearbox with overdrive (4 synchro):  6 Imp pints (7 US pints, 3.4 litres) 20/50 multigrade.
Three-quarter floating rear axle (Banjo):  2.25 Imp pints (2.75 US pints, 1.28 litres) Hypoid SAE90EP.
Salisbury semi-floating rear axle:  1.5 Imp pints (1.8 US pints, 0.85 litres) Hypoid SAE90EP.
Automatic gearbox:  10.5 Imp pints (12.7 US pints, 6 litres) Auto Trans fluid Type F.
Steering rack:  1/3rd Imp pint (0.19 litres, 0.39 US pints) SAE 90 gear oil.
Coolant:
Up to Nov 1967 (back filler radiator):  9.5 Imp pints (11 US pints, 5.4 litres). 7lb/sq. in. filler cap.
Nov 1967 to June 1976 (centre filler radiator): 11.5 Imp pints (13.8 US pints, 6.6 litres). 10lb/sq. in. filler cap.
June 1976 on:  12 Imp pints (14.4 US pints, 6.8 litres). 13lb/sq. in. filler cap.
Standard thermostat: 82°C (180°F) with 74°C (165°F) for hot climates and 88°C (190°F) for cold climates.
 The coolant should be mixed in accordance with the manufacturers instructions for the prevailing climatic conditions and changed at the recommended intervals.
Lubrication Charts:
For a lubrication chart RHD and LHD except North America follow this link.
For a lubrication chart North America follow this link.

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