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Technical History of the Mini 1959-1975
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Technical History of the MINI 1959-75
August- Austin Seven announced (ADO 15). First chassis A/A2S7 101. Morris Mini Minor announced. First chassis M/A2S4 1010. Engine 62.94mm bore, 68.26mm stroke, 848cc displacement, 34 HP net. Gear ratios 3.627/1 ; 2.172/1; 1.412/1 ; 1/1. Final drive 3.765/1. Brakes 7" diameter x 1-1/4" wide single leading shoe.
April- shorter drive shafts with involute form instead of square splines and modified flanges.
May- Mini van announced. Changes to sedan during first year. Oil-control rings improved optional distributor for use with regular grade fuel. Improved air cleaner. Changes to clutch throughout stop. Stronger reverse- detent-plunger spring. Larger front wheel bearings. Improved shock absorber mountings. Fuel tank drain plug. Cranked gear lever.
September- Mini Countryman/Traveler announced. 6-1/2 gallon fuel tank in sedan position. Spare wheel and battery under false floor in the rear.
April- Mini pickup truck announced
May- Alternative cast aluminum suspension trumpets introduced.
August- 16 blade fan to reduce fan noise.
Autumn- Seat belt mounts. Improved oil and fuel pumps. Wheel thickness increased from 0.080 to 0.120 inch. Better synchromesh.
September- Improvement from chassis numbers. A/A2575 125538, M/A2545 75533. Super models. Trim improvements. Grill, two tone paint. Chrome frames on side windows, tubular extensions to overriders (bumpers). Addition of oil pressure and water temperature gauge. ignition key start instead of floor button. Chrome gear lever. Cooper Mini announced (ADO 50) at chassis number C/A257 138031 K/A254 13811. Engine 62.43mm bore x 81.28mm stroke. 997cc displacement 55HP gross. Twin 1-1/4" HS2 SU carburetor. Main difference to 848 engine - longer duration camshaft. Compression ratio up 8.3 to 8/1. Crankshaft tail up from 1-3/8" - 1-1/2". Crankshaft torsional vibration damper. Different cylinder head casting with slightly improved porting and bigger inlet valves plus double springs. Larger bore exhaust system and revised 3 into 1 exhaust manifold. Ignition key start instead of floor button start. Gear ratios 3.200/1; 1.916/1; 1.357/1; 1/1. Final drive 3.765. Front brakes 7" diameter x 1/4 think discs.
October- Wolseley Hornet and Riley Elf introduced at chassis numbers W/A251 156861, R/A251 156851. Difference from 848 Mini- revised front and rear styling. 2-1/2 cubic feet of extra luggage space. Ignition key start. Waterproof cover for distributor.
January- Austin Seven becomes Austin Mini. During year improvements- improved shocks. Waterproof cover for distributor. 1/10 reading odometer. Nylon seating for float chamber needle valve. Thicker gauge silencer casing. Plastic bush top of steering column instead of felt. Change of pressure-limiting valve in brake system to rear brakes plus increase slave-cylinder diameter. Plastic oil-filler cap on engine.
October- Super and Deluxe models merged to form Super Deluxe at chassis numbers A2575 307125 7/A2545 148817. Baulk-ring synchromesh box progressively introduced at engine 406522. All steel Countryman/Traveler introduced at chassis numbers AW7, M/AWH 308939. End of Year dry crank and Deva bush introduced in place of oil fed item at engine number 551624.
November- Hornet/Elf MKII introduced at chassis numbers R/A252 369601, W/A252 367151. Major changes- new short-stroke engine. 64.58mm bore x 76.2mm stroke. Displacement 998cc.
March- Front Brakes- Twin leading shoe 1-1/2" wide. Cooper S introduced at chassis number C/A257 384101, K/A254 384601. Engine- 70.6mm bore x 68.26mm stroke. 1071cc displacement. 70 HP gross. Completely redesigned engine with different head, block, crank, rods, pistons, etc. Other changes- Servo assisted front disc brakes. 7 -1/2" c 3/8" thick discs. nitrided crankshaft with main bearings up from 1.75" to 2.00" diameter and main bearing width reduced 1/8". Bore spacing altered by 1/4". Improved oil pump, ventilated wheels, different rear drums with built in spacers, 4-1/2" wheels optional, radial tires. Mini cooper- improved disc brakes.
May- Improved sliding-window catches.
January- Cooper 997 discontinued at chassis numbers C/A257 L189222, K/A254 L187907. 998 Cooper introduced at chassis numbers C/A 257 502447, K/A254 502482. 998 Cooper engine was virtually the same as the Hornet/Elf unit introduced in March 1963, but utilized a new head casting with greatly improved flow. This was used together with a milder camshaft than the 997 unit.
March- 970 introduced at chassis numbers C/A257 549501, K/A254 550501. 1275 Cooper S introduced at chassis numbers C/A 257 551501, K/A254 552501. At engine no.9F.SA.X.29001. Diaphragm clutch replaced spring clutch, 3.44 final drive for 1275 S, 4-1/2" rim wheels optional, oil-filter warning light.
August- 1071 Cooper S discontinued at chassis numbers C/A257 563570, K/A254 563500.(last engine number 9FD.SA.H.33948.)
September- Major change to hydro-elastic suspension from the dry rubber cone suspension. applied to all models except countryman and traveller. Other changes include courtesy lights, plastic frame interior mirror, key start on all models, safety sun visor. All 850 models changed to twin leading shoe brakes. Closer ratio box B type gears used throughout the range. Needle roller bearings used for third motion shaft gears. Increased gear width and larger bearings at chassis numbers A/A2S7 640203, A/AW7 638559, M/A2S4 296257, M/A2S4/S 296257, M/AW4 638879, R/A252 639909, W/A252 625740, C/A2S7 6133719, K/A2S4550743, C/A2S7 549763, K/A2S4 550793, C/A2S7 552243, K/A2S4 553170. Diaphragm clutch fitted to all 850 engines from engine number 883708 plus twin leading shoe brakes. 3 Position seat brackets fitted to driver's seat on all models. Diaphragm spring clutch on all 998 units.
January- 970 Cooper S discontinued at chassis numbers C/A2S7 549992, K/A2S4 550980, 13 gills/inch radiator replaced by 16 gills/inch radiator on Cooper.
October- Automatic gearbox option for Austin/Morris 850 used together with increased compression ratio and single HS4 1-1/2" SU carburetor.
November- Reclining seat option on Cooper and Cooper S.
January- Sealed beam headlights and safety bosses on door handles on all models. Cooper S models fitted with twin rear tanks, oil coolers and a different camshaft. October- Elf/Hornet III introduced with improvements: face level ventilation, concealed door hinges, windup windows, remote gear change, push button interior door handles. Front pannier boxes modified but retained. Partial introduction of all synchrobox on Cooper S (not 100% until 1968).
October- Mini MKII (all Models) Introduced. External change includes restyled grill and larger tail lights. Mechanical changes, turning circle reduced from 32 to 28 feet. (29ft for countryman/traveler). Steering rack with 25 teeth instead of 15. Effective length of steering arm and offset altered. Wheel cylinder sizes changed for lighter brake action. Multi-switch steering column stalk. Rear window 1-1/2" wider. Self parking wipers. Improved instrument layout. Switches moved nearer driver. Remote change for 998 minis plus 3.44 final drive. Plastic fan fitted on all models. 848cc Basic retains original long gear lever. Modified case on long lever to standardize A/A2SB 1068051. 848cc Super Deluxe supplied with remote change. A/A2SB/S 1068001. Automatic transmission available on all models except Cooper S. 1000 Super deluxe sedan and Countryman /Traveler (with and without wood trim) introduced. Single carb 998 with Cooper type gear change and MKII body.
September- Four synchromesh gearbox introduced throughout range. At engines: 850 units- 8AM/We/101 onwards, 8AM/Te/101 onwards, 8AJ/We/101 onwards, 85H/ /101 onwards. 998 mini- 99H/ /101 onwards, 998 cooper- 9FD/Xe/101 onwards. 1275 S-9F/Xe/Y51501 onwards. Gearbox ratios now: mini- 3.525/1, 2.218/1, 1.433/1, 1/1. Mini Cooper S- 3.3/1, 2.074/1, 1.353/1, 1/1. Permanent- magnet wiper motors fitted.
April- Heated rear window option on 850/998 Cooper and S models.
August- Hornet and Elf. Austin and Morris 850 MkII production ceased.
September- Austin and Morris 1000 MkII production ceased. Mini 850 + 1000 and MKIII Cooper S announced. These came into line with Clubman range, with windup windows, concealed hinges, dry suspension, offset wipers, negative earth /ground.
October-Clubman range introduced. Engine units;- 998cc or 1275cc in 1275 GT version (note this was not an S engine and it used a single carb). Exterior changes- Restyled front end giving 4" increase in length. 4-1/2 " rims standard in rostyle pattern. Separate side lights. Offset wipers. Mechanical changes- S brakes on 1275 models, twin leading shoe on 998 units, wind up windows and concealed hinges, face ventilation. Instruments in console directly in front of driver. Three spoke steering wheel. Negative ground. 3.65 drive on 1275 unit. MKII Super deluxe replaced by mini 1000 with wind up windows. Dry suspension, negative earth/ground. Mechanical fuel pump. MKII Countryman/traveler discontinued (replaced by clubman estate).
November- MKII Mini S Cooper production ceased.
October- Ignition shield fitted throughout range.
December- Steering column lock introduced throughout range.
February- Final drive on 1275 GT changed from 3.65 to 3.44 at engine 12H 389SH6091.
July- Clubman saloon changed to dry suspension at commission S20S-48645A. 1275 GT changed to dry suspension at commission S20D-8156A. During year- MKIII Cooper S production ceased. Radiator cowling in wing removed. Factory fitted seat belts .
December- Alternator fitted as standard.
January- Radial-ply tires on all models. New rod change gearbox introduced with a revised floor pressing to accommodate it.
May- New 'pot' type CV joints on inboard end of drive shaft (all models except clubman)
July- New 'pot' type CV joints on inboard end of drive shaft on clubman models. Improved door check pivot brackets on all models.
October- Low octane distributor for 850 engine discontinued.
February- Inertia reel seat belts as standard on all models.
April- Heater as standard in 850.
May- HS4 carburetor fitted on revised manifold to 850 & 1000 models. Special air intake temperature control device fitted to 1275 models.
June- Optional laminated screen on 1275 Clubman.
August- Optional DeNovo safety wheel or conventional 12" wheel & tire used together with bigger non-servo disc brakes 1275 clubman only.
October- All models 88'C thermostat. New seats with anti-tip catches on 850. Reclining seats standard on 1275 clubman. Special limited edition mini 1000 with the following as standard: Orange strip cloth seat trim. Reclining front seats, Safari carpets. Two chrome door mirrors. Coach line on waist. Finished in Brooklands green with glacier white. 998 Clubman available with 1098cc engine given by increased stroke length of 0.3" stroke now 3.3" (83.8mm)
Notes on Chassis Numbers
W denotes Wolseley
R denotes Riley
Austin 850 MK 1 prefix A/A2S7
Morris 850 MK 1 prefix M/A2S4
Austin 850 MK l prefix A/A2SB
Morris 850 MK l prefix M/A2S6
Austin cooper MK l prefix C/A2S7
Morris Cooper MK l prefix K/A2SB
Austin Cooper MK 2 prefix C/A2SB
Morris Cooper MK 2 prefix K/A2S6
Austin Cooper S MK l prefix C/A2S7
Morris Cooper S MK l prefix K/A2S4
Austin Cooper MK 2 prefix C/A 2SB
Morris Cooper MK 2 prefix K/A2S6
Note: No chassis differences between Cooper and Cooper S models.
C denotes Austin in Cooper range and K denotes Morris.
S denotes a Super, eg A/A2S7/S is a Super model.