MGB Specification

Article written by Skye Nott. Published on 2006-04-02
MG Experience Library – Reference Section
The contents of this article are © Copyrighted and published under the following terms:
Copyright © the author and published by permission or under fair use.

Dimensions & Weight

MGB Dimensions & Weight Specification
Wheelbase:	91 in
Track - front:	49.0 in
Track - rear:	49.25 in
Overall length:	153.2 in
Overall width:	59.9 in
Overall height:	49.4 in
Ground clearance:	4.2 in
Turning circle:	32 ft
Curb (dry) weight:	1962	2080 lbs
	1968	2220 lbs
	1980	2335 lbs
Test (wet) weight:	1962	2400 lbs
	1968	2590 lbs
	1980	2505 lbs

Chassis

Unit Construction body, welded steel constuction, front suspension on subframe.

Steering

Cam Gears, rack & pinion system.

MGB Steering Specification
Turning circle: Steering ratio: Turns lock-to-lock: Castor angle: Camber angle: Kingpin angle: Toe in: Grade of oil:	32 ft (to car 410000, 06/1976) ? (from car 410001) 21.4:1 (as above) ? 2.9 (as above) 3.5 7° 1° 8° 0.1875 in SAE 90EP Hypoid

Brakes

Disc brakes front, drum brakes rear.

MGB Brakes Specification
Disk size front: Drum size rear: Parking brake: Method of operation:	10.75 in 10 in Cable operated, rear Hydraulic, vacuum servo assisted as option to 1973, standard thereafter. Dual system some markets from '67.

Suspension

Armstrong lever shocks at 4 corners, integral upper control arm at the front, linked to leaf spring retaining plate at the rear.

MGB Suspension Specification
Grade of oil:	20wt motorcycle fork oil (approximate)

Wheels

Either steel disc bolt-on, or Rudge type wire spoked. Late cars had alloy wheels as option (Rubery Owen aka "Rostyle").

MGB Wheel Specification
For MkI, MkII-on: Rim size: Tyre Size: Tyre pressure: Wheel bolts:	Wires 4J * 14, 5J * 14, 4.5J * 14 5,60 * 14, 165 * 14 (approx 175/70HR14 or 185/70HR14) 21 psi front, 24 psi rear (+4 for highway) 4 on 4-1/2"

Engine

4 cylinder in line, pushrod, single cam.

High or low compression depending on market.

MGB Engine Specification
Bore: Stroke: Cubic capacity: Main bearings: Oil pressure: Grade of oil: Sump Capacity: Firing Order: Compression ratio HC: Compression ratio LC: Compression HC: Compression LC: Valve size in/ex: Cam timing: Power output:	80.26mm 88.90mm 1798cc 18G, 18GA - 3 18GB on - 5 ~70psi at 3000rpm ~50psi idle SAE 20W50 7.5 pints 1-3-4-2 18G - 8.8:1 18V - 9.0:1 8.0:1 18G - 160psi 18V - 170psi 130psi 18G, 18V 74 on - 39.8mm/34.1mm 18V to 74 - 41.3mm/34.1mm 18G - 16/56 51/21 18V - 20/52 55/17 See performance section in Library.

Ignition Timing

Varies with Engine spec, see above.

MGB Ignition Specification
Distributor points gap: Dwell: Spark plugs: Spark plug gap:	0.015 in 60° NGK BP6ES or Champion N9YC 0.025 in (0.030 in or more with Sport coil) 0.035 in (after 1975)

Carburetter Type

MGB Carburetor Specification
1963 - 1971: 1972 - 1974: 1975 - 1980:	Twin SU HS-4 Twin SU HIF-4 Single Zenith-Stromberg
Jet size, main: Needle & Springs:	SU 0.090 in Zenith: 0.100 Various according to carburettor spec.

Clutch

Borg & Beck type, single dry plate.

MGB Clutch Specification
Material: Number of springs:	Ferodo Single Diaphragm

Gearbox

Four speed manual, synchromesh on top three ratios to 1965, all synchro after. Electrical overdrive optional, standard from 1975. Borg Warner 35 automatic gearbox was also available 1967 to 1973.

MGB Transmission Specification
	18G-18GB (to Oct67)	18GD-18V/780 (Nov67-Nov74)	18V/797-18V/847 (Dec74-May76)	18V/846-18V/893 (Jun76-)
First:	3.6363:1	3.440:1	3.036:1	3.333:1
Second:	2.2143:1	2.167:1
Third:	1.3736:1	1.382:1
Third O/D:	1.101:1 to 18GD, 1.133:1 18GF on
Top:	1.00:1
Top O/D:	0.802:1 to 18GD, 0.82:1 18GF on
Reverse:	4.7552:1	3.095:1
Grade of oil:	SAE 20W50 (same as engine)
Capacity:	4.5 pints, 4.7 pints, 6 pints. Add ~3 pints when O/D fitted

Propellor Shaft

Open shaft, needle roller universal joint at each end with grease zerks.

Final Drive

Live axle, hypoid bevel gears. "Banjo" type to Jun-67, "Salisbury" type onwards. Open differential.

MGB Differential Specification
Ratio:	Manual:	3.909:1 (all years)
	Auto:	3.7:1
	MGC:	Early manual:	3.07
		Early auto & o/d: Late manual:	3.307
		Late o/d:	3.70
MPH per 1000rpm:	Manual top:	17.9
	Top O/D:	22.1
	Auto:	18.91
Grade of oil:	SAE 90EP Hypoid
Capacity:	1.5 pints

Cooling System

Pressurised, thermostatic control, pump assisted. Water/antifreeze mix.

MGB Cooling System Specification
Capacity:	12 pints
Cap Rating:	1962-67	7 lbs
	1968-75	10 lbs
	1976	13 lbs
	1977-80	15 lbs

Fuel System

Tank located at rear of car under boot (trunk) floor.

Pump SU points-type, attached to battery bracket on right hand side, in front of rear wheel, under body.

MGB Fuel System Specification
Tank capacity:	12 gallons (?)
Pump pressure:	2-4 psi (static)
Pump rate:	SU HP	31.8 Lph
Pump rate:	SU AUF 300/305	68.2 Lph

Production Data

For a more complete description of the VIN plate found on the dash and the engine number, please visit the MGB VIN FAQ.

Model Year	1st Month	Car #		Body #		Engine #
Model Year	1st Month	RD	GT	RD	GT	Engine #
1963	5/62	101		MGB/101		18G/ /HL101
1964	8/63	19586		MGB/26813		18GA/ /HL101
1965	10/64	48766		??		18GB/ /HL101
1966	10/65	71441(?)	71933	??	GBD/101	18GB/ /HL101
1967	11/66	108039	??	??	??	18GB/ /HL101
1968	10/67	138401	139472	MGBU/101	GBUD/500101	18GF/ /HL101
1969	10/68	158371	158233	MGB/14588#	??	18GH/ /HL101
1970	10/69	187211	187841	MGBU/27359	GBUD/510630	18GH/ /HL22209 18GJ/ /HL101
1971	9/70	219021	219335	MGBU/300101	GBUD/520235	18GK/ /HL101
1972	5/71	258001	258004	MGBU/400101	GBUD/620101	18V/584Z/L101 18V/585Z/L101(OD)
1973	8/72	294251	296001	MGBU/500101	GBUD/720101	18V/672Z/L101 18V/673Z/L101(OD)
1974	8/73	328101	328801	MGBU/600101	GBUD/820101	18V/672Z/L14891# 18V/673ZZ/L14891(OD)#
1975	12/74	367901	??	GU23T/7707	??	18V/797AE/L101 18V/798AE/L101(OD)
1976	9/75	386601	??	GU23T/50101	??	18V/801AE/L101 18V/802AE/L101(OD)
1977	6/76	410001	410351	GU23T/760000	??	18V/883AE/L101 18V/884AE/L101(OD)
1978	9/77	447001	??	GU23T/860000	??	18V/890AE/L101 18V/891AE/L101(OD)
1979	6/78	471001	??	GV23T/960000	??	18V/883AEL/29033#
1980	6/79	501001	??	GV23T/984080	??	18V/883AEL/43540#
# These numbers are approximate. Thanks to Caroline Robinson (University Motors), Moss Motors, and Victoria British If you have any of the missing numbers please contact me!

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Detailed Specification

Under Construction - Incomplete

Usual disclaimers apply. It is wholly possible I have made typographical errors in the numbers below.

Make sure to double check the figures before doing any work and let me know if you find any errors so I can correct them.

Thanks, Skye N. (Webmaster)

Engine
ENGINE SPECIFICATION & DATA - 1798 c.c. TYPE 18G & 18GA
Engine - General
Type	4 cylinder in line O.H.V. pushrod operated 18G or 18GA
Bore	3.16 in. (80.26 mm.)
Stroke	3.5 in. (89 mm.)
Cubic Capacity	1789 c.c. (109.8 cu. in.)
Compression Radio : High C	8.8 to 1
Low C	8.0 to 1
Compression Pressure : High C	160 lb./sq. in. (11.25 kg./cm².)
Low C	130 lb./sq. in. (9.15 kg./cm².)
Torque : High C	110 lb./ft. (15.2 kg.m.) at 3,000 r.p.m.
Low C	105 lb./ft. (14.5 kg.m.) at 3,000 r.p.m.
Engine Idle Speed - Optimum	500 r.p.m.
Firing Order	1,3,4,2
Location of No.1 Cylinder	Next to radiator.
Engine Mountings	3 - one each side of the engine, one under the gearbox
Camshaft and Camshaft Bearing
Camshaft Drive	From crankshaft by double roller chain
Camshaft Bearings	Three - white metal replaceable liners
Camshaft Journal diameter:
Front	1.78875 to 1.78925 in. (45.424 to 45.437 mm.)
Centre	1.72875 to 1.72925 in. (43.910 to 43.923 mm.)
Rear	1.62275 to 1.62325 in. (41.218 to 41.230 mm.)
Camshaft bearings internal diameter after reaming in position in block:
Front	1.79025 to 1.79075 in. (45.472 to 45.485 mm.)
Centre	1.73025 to 1.73075 in. (43.948 to 43.961 mm.)
Rear	1.62425 to 1.62475 in. (41.256 to 41.269 mm.)
Diametrical clearance	.001 to .002 in. (.0254 to .0508 mm.)
End float	.003 to .007 in. (.076 to .178 mm.)
Cam lift	.250 in. (6.35 mm.)
Timing Chain	3/8 in. (9.25 mm.) pitch by 52 pitches
End thrust	Taken by locating plate
Connecting Rods & Big & Little End Bearings
Type	Angular split big end, split clamp small end
Length between centres	6.5 in. (165.1 mm.)
Big end bearings - Type	Shell
Big end bearings - Material	Steel backed copper-lead
Big end bearings - Length	.995 to 1.005 in. (25.2 to 25.52 mm.)
Big end bearings - Clearance	.001 to .0027 in. (.0254 to .068 mm.)
Endfloat on crankpin	.008 to .012 in. (.20 to .30 mm.)
Undersizes available	-.010, -.020, -.030 and -.040 in. (-.254, -.508, -.762, -1.016 mm.)
Crankshaft & Main Bearings
Main journal diameter	2.1265 to 2.127 in. (54.01 to 54.02 mm.)
Crankpin journal diameter	1.8759 to 1.8764 in. (47.648 to 47.661 mm.)
Crankshaft end thrust	Taken by thrust washers at centre main bearing
Endfloat	.002 to .003 in. (.051 to .076 mm.)
Main bearings	Three shell type
Bearing material	Steel backed copper-lead
Bearing length	1 1/8 in. (28.5 mm.)
Diametrical clearance	.001 to .0027 in. (.0254 to .068 mm.)
Undersizes available	-.010, -.020, -.030 and -.040 in. (-.254, -.508, -.762, -1.016 mm.)
Cylinder Block
Type	Cylinder cast integral with top half of crankcase
Water jackets	Full length
Oversize bores : First	.010 in. (.254 mm.)
Max.	.040 in. (1.016 mm.) (** .060 and .090 now available)
Cylinder Head
Type	Cast iron with vertical valves
Port arrangements	Inlet & exhaust ports on same side
No. of ports : Exhaust	2 separate and one siamesed
No. or ports : Inlet	2 siamesed
Combustion chamber capacity	42.5 to 43.5 c.c. (2.59 to 2.65 cu. in.) with valves fitted
Gudgeon Pin
Type	Semi-floating. Held by clamp bolt
Fit in piston	Free push fit at 20°C (68°F)
Outer diameter	.7499 to .7501 in. (19.04 to 19.05 mm.)
Lubrication System
Type	Pressure and splash. Wet sump
Oil filter	Full flow. Tecalemit felt element.
Capacity Oil Filter	1 pint. (1.2 U.S. pints, .57 litre)
Sump capacity	7 1/2 pints (.42 litre, 9 U.S. pints)
Oil cooler capacity	3/4 pint (.42 litre, .9 U.S. pints)
Oil pump - Type	Hobourn-Eaton or eccentric rotor.
Pump capacity	3 1/4 gallons a minute @ 2,000 r.p.m.
By-pass valve opens	12 to 17 lb./sq. in. (4.9 kg./cm².)
Oil pressure relief valve opens	70 lb./sq. in. (4.9 kg./cm².)
Oil pressure relief valve spring - free length	3 in. (76.2 mm.)
Oil pressure relief valve spring - fitted length	2 5/32 in. (54.7 mm.)
Relief valve spring - load at fitted length	15.5 to 16.5 lb. (7.0 to 7.5 kg)
Normal oil pressure - Idling	Not less than 15 lb./sq. in. (1.05 kg./cm².)
Normal oil pressure - 3,000 r.p.m.	Not less than 50 lb./sq. in.
Pistons
Type	Aluminium - Solid skirt
No. of rings	4. 3 compression, 1 oil control
Clearance in cylinder : Top	.0036 to .0045 in. (.091 to .121 mm.)
Clearance in cylinder : Bottom	.0018 to .0024 in. (.045 to .060 mm.)
Width of ring grooves : Top Second Third Oil control	.064 to .065 in. (1.625 to 1.651 mm.) " " .1578 to .1588 in. (4.008 to 4.033 mm.)
Gudgeon pin bore	.7501 to .7503 in. (19.052 to 19.057 mm.)
Piston oversizes available	+.010 in., +.020 in., +.030 in., +.040 in. (+.254 mm., +.508 mm., +.762 mm., +1.02mm.)
Piston Rings
Top compression ring	Parallel - Cast iron - molybdenum filled
2nd. and 3rd. compression rings	Tapered - Cast iron - molybdenum filled
Top ring width	.0615 to .0625 in. (1.562 to 1.587 mm.)
2nd. and 3rd. ring width	.0615 to .0625 in. (1.562 to 1.587 mm.)
Top ring fitted gap	.012 to .017 in. (.304 to .431 mm.)
2nd. and 3rd. rings fitted gap	.012 to .017 in. (.304 to .431 mm.)
Groove clearance	.0015 to .0035 in. (.038 to .088 mm.)
Oil control ring	Slotted scraper
Oil control ring - Width	.1552 to .1562 in. (3.94 to 3.96 mm.)
Oil control ring fitted gap	.012 to .017 in. (.304 to .431 mm.)
Groove clearance	.0016 to .0036 in. (.04 to .09 mm.)
Tappets
Type	Barrel with flat base
Outside diameter	13/16 in. (20.64 mm.)
Length	2.293 in. to 2.303 in. (58.25 to 58.5 mm.)
Rocker Gear
Length of Rocker Shaft	14 1/32 in. (356 mm.)
Diameter	.624 to .625 in. (15.85 to 15.87 mm.)
Rocker arm bore	.7485 to .7495 in. (19.01 to 19.26 mm.)
Rocker arm bush - inside diameter	.6255 to .626 in. (15.8 to 15.9 mm.)
Ratio	1.4 to 1
Valves
Head diameter - Inlet	1.562 to 1.567 in. (38.67 to 38.80 mm.)
Head diameter - Exhaust	1.343 to 1.348 in. (34.11 to 34.23 mm.)
Valve seat angle - Inlet & Exhaust	45 ½°
	....... currently incomplete

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~ MGB Specification ~

Article by Skye Nott – Published 2006-04-02

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