Technical Data & Specifications

Whilst every attempt has been made to ensure the data are correct, the contributors to this site cannot be held responsible for the information.  Specific information is also given in the Austin Motor Co. handbook for each model.  Much more detail can be found in 'The Austin Seven Source Book' by Bryan Purves.  Pub: Haynes Publishing, Sparkford, Yeovil, Somerset.   ISBN 0 85429 557 7.  Also see 'Austin Seven Companion' published by the 750 MC.

If any 'Seven' enthusiast feels that the data should be corrected, or extended, please contact CA7C

Engine Data;    Gearbox Data;    Transmission Data;
Chassis and Suspension Data;     Electrical Data:   
Engine output;    Fuel consumption;
Austin Seven Threads;    Torque Values

Engine Data

Engine specification

  Austin Seven Big Seven
Bore 2.2" (55.88 mm) 2.235" (56.77mm)
Stroke 3"   (76.2 mm) 3.5" (88.9mm)
Capacity - standard 747.5 cc 900cc
Compression Ratio (up to mid 1936) 4.8 : 1  
Compression Ratio (post mid 1936) 6 : 1 6 : 1
Oil Pressure (Hot) 2 - 5 lb psi 25 - 30 lb psi


 Timing

    Notes
Pre 1935 1 7/8" B T D C (20 degrees)
Mk1 Ruby engine   3/4" B T D C at flywheel Points should be just opening.
MK 2 Ruby engine TDC Tappet clearance for valve timing 0.004"
Big Seven TDC Tappet clearance for valve timing 0.004"
Firing Order 1 3 4 2  
Contact breaker points 1929 - 1931  0.020" CAV electrics
Contact breaker points 1932 - 1936  0.014" Lucas electrics
Contact breaker points 1936 - 1939  0.012" Lucas electrics
Champion No 7 Sparking Plugs 1922 - 1936 Low compression engine
Champion L10 Sparking Plugs. 
Now replaced by Champion L86C
1936 - 1939 High compression engine
Sparking plug gap 0.018" for mica;
0.022 - 0.025" for corundite
 

Carburettor Settings

  Austin Seven Big Seven
Choke tube 17 23
Main jet 57 90
Compensating jet 50 50
Slow-running jet 60 60
Progression jet 50 125
Capacity tube 2 -
Needle valve setting 1.5 1.5
Economy jet - -
     


Valve clearances

Inlet - standard engine 0.004"  Hot 0.006" Cold
Exhaust - standard engine 0.004  Hot 0.007" to 0.008" Cold
Inlet - sports engine 0.004" to 0.006" Hot 0.008" Cold
Exhaust - sports engine 0.006" to 0.008" Hot 0.010" Cold

Big End Bearings - Standard engine not pressure fed
Big end clearance to crank pin  0.001" to 0.002" Optimum clearance
Crank pin out of round  0.003" Preferred maximum
Big end nuts torque around 20 ft. lbs.  

Small End Bolts

Small end bolts Bolt Heads should face off-side of engine

Camshaft

End float   0.002"   

Lubrication

Normal Oil Pressure - 2 bearing crank up to 5 p.s.i.  
Normal Oil pressure - 3 bearing crank up to 5 p.s.i.  
Oil filter  Gauze in sump Clean every 4000 - 5000 miles
Oil grade S.A.E. 30 or equivalent (avoid detergent oils) in an engine that has not been totally cleaned.
Sump capacity standard engine 4 pints  
Sump capacity sports engine 8 pints
 

Cooling System

Capacity 9½ pints approx Big Seven 13 pints approx

Pistons & Rings

Split skirt piston   Split on nearside of engine
Piston to cylinder clearance 0.0015" Split skirt piston 
Piston to cylinder clearance 0.004" Plain skirt piston 
Ring Gap 0.003" to 0.006"  
     

 

 

Gearbox Data

Lubrication

Oil grade - standard S.A.E. 40  Multigrade 20W-50 is commonly used now.
Oil grade - sports S.A.E. 50  
Oil capacity 1922 - 1932 2/3 pint  
Oil capacity 1933 - 1939 1½ pints  
     

Transmission Data

Rear Axle

Oil grade - standard 140 grade Big Seven requires EP140 Oil
Oil Capacity 7/8 pint   
     

 

Chassis and Suspension Data

Front Springs

1924 - 1925 5 leaves 30" bush centres
1926 - 1929 5 leaves 29 1/4" bush centres
1929 - 1934 8 leaves 29 1/4" bush centres
     

Rear Springs

Pre 1935 6 leaves 23 1/4" hole to bush centres
1926 -1934  7 leaves 23 1/8" hole to bush centres
     

 

Electrical Data

Dynamo

1922 - 1928 C.A.V. dynamo Output approximately 5 to 6 amps
1928 Lucas Short dynamo
1929 - 1932 Lucas Longer dynamo
1931 - 1935 Lucas C35A Brushes without leaves
1935 - 1939 Lucas C35M Brushes with leaves
     

Distributors

Sept 1928 ? Both Lucas and alternative fitted
late 1931   Lucas DJ4 Manual advance
July 1934 - 1936 Lucas DK4A Auto Advance  3 degrees
July 1936 - 1939 Lucas DK4A Auto Advance  8 degrees
     

 

Engine output

Saloon models

Year bhp rpm
1922 10 2400
1923 - 32 10.5 2400
1933 - 1934 12 2600
1935 13.5 3000
1936 16.5 3400
1937 -39  Big Seven 25 4800

Sports models

Year bhp rpm
1930 - 31 24 5000
1930 - 31  supercharged 33 5000
1933- 34 21 4400
1934  Speedy 23 4400
1935 - 37 23 4000


Fuel consumption

Saloon models

Year mpg
1923  
1927 - 31 45 - 50
1931 - 1933 45
1934 45 - 50
1934 - 35 40
1937 40 - 42
1937 - 1939  Big Seven 40 - 43

 

Torque Values
Torque values are not mentioned in the Austin Motor Co. Handbooks.  Do-it-yourself Austin Seven owners in the 1930s did not have a torque wrench and used the standard Austin spanners supplied with the tool kit.  Many owners still prefer to use a spanner without overtightening as it is too easy to cause damage to the threads using other tools.

Torque values for tightening cylinder head nuts on the Austin Seven and Big Seven were published in the Austin Service Journal (July or Aug 1937, exact reference not known), supplied to on a confidential basis to Agents & Service Depots.

Torque Values

Model Size of Stud Torque Required *
Seven 5/16" BSF 360 lbs/in
Big Seven 3/8" BSF 550 lbs/in

* please check with http://www.unitconversion.org/unit_converter/torque.html if you are using metric.

Seven 747cc engine:
Values for tightening cylinder head nuts, 50 lbs/ft for centre main bearing and 18 lbs/ft for big ends, have been discussed by many enthusiasts on Austin Seven Friends forum at http://pub25.bravenet.com/forum/static/show.php usernum=2099944454&frmid=5&msgid=891266&cmd=show

There is further discussion at http://myweb.tiscali.co.uk/speedex/index_files/Page2295.htm and at http://www.austinsevenownersclub.com/forum/viewtopic.php?f=7&t=1762

The 'Austin Seven Companion' at page 273 gives 30 lbs/ft maximum for tappets.

Big Seven 900cc engine:
The figures given are for 3/8" dia. stud/bolt diameter.  The 550 lbs/in, which equals to 45 lbs/ft, is the setting for a new engine but it is better not go above 35 to 38 lbs/ft due to the age of either the stud or the threads in the block.  Values for tightening main bearings and big ends are not available (source Robin Taylor - Big Seven Registrar.)


NB:
Great care must be taken when using spanners and especially with sockets and extension bars.  It is too easy to strip a thread, particularly in the aluminium components.  Spanners usually have a length that is appropriate to their size; grip the spanner and use the strength in your wrist to tighten the nut/bolt.  Do not put your bodyweight behind it and heave on the spanner; if you do disaster is sure to follow!

When tightening wheel nuts use the wheel brace that came with car, don’t use a spider or torque wrench.  Don’t be tempted, when using a socket and bar, to slip a piece of tube over the bar to get extra leverage.  It is a method which may be helpful when trying to undo something but never when tightening.  Make regular checks before outings.

 

Austin Seven Threads

The following information has been obtained from a 1932 LWB Box Saloon, variations may have been used by Austin during the production history of the Seven.

Size Type TPI Use
1/4 BSF 26 General Bolts and Setscrews. Engine/ Manifold Studs.
5/16 BSF 22 General Bolts and Setscrews. Engine/ Cylinder Head and Gearbox Studs. Shock Absorber Link Bolts
3/8 BSF 20 Bolts and Setscrews . Wheel Studs. Shock Absorber Link Bolts. Dynamo Spindle Com End. Springs "U" Bolts.
7/16 BSF 18 Dynamo Spindle/Castle Nut. Front Brake Shoe Pivot Pin.
1/2 BSF 16 Steering Swivel Axle/Cross Tube Levers. Brake Pedal Fulcrum Pin. Rear Spring Through Bolts.
1/4 BSW 20 Oil Sump Bolts.
5/16 BSW 18 Studs Crankcase/Bell-housing. Oversize Sump Bolts.
3/8 BSW 16 Studs Bell-housing (Stepped Oversize).
2 BA 31.4 Fittings. Door Hinges Mounting ("A" Post).
3/4 SPECIAL 14 Drain Plugs Gearbox/ Engine/Back Axle and Gearbox Filler Plug.
3/4 BSC ? 20 Steering Cross Tube and Jaws. Plug Top of King Pins.
5/8 SPECIAL 16 Axle Shafts / Radius Arms/Crankshaft (front)
7/8 SPECIAL 12 Crankshaft (rear)
1–1/4 SPECIAL 16 Rear Hub Bearing Retaining Nut. Torque Tube Socket. Screw Cores Engine Block.
1–3/8 SPECIAL 16 Hubs.
3/4 BSC/BSB 26 Gearbox Speedometer Drive Bush and Cable Ends.
3/8 BSC 26 Front and Rear Shock Absorbers Centre Bolt.
7/16 BSC 26 Headlamp Mounting Bolts/Nuts.
1/2 BSC 26 Starter Motor Spindle/Nut. Replacement Front Shock Absorber Centre Bolts.
1/8 BSP 28 Shackle Repair. Grease Plug Hole-Hubs. Grease Nipples Fitting Holes.
1/4 BSP 19 Pipe/Fittings. Brake Rope Guides. Rear Axle Filler Plug. Rear Axle Breather Pipe. Petrol Pipes Unions.
3/8 BSP 19 Speedometer Drive Bush Gearbox.
       

These abbreviations have been used.

BA = British Association  BSP = British Standard Pipe
BSB = British Standard Brass BSW = British Standard Whitworth
BSC = British Standard Cycle SPECIAL = Whitworth Form Special
BSF = British Standard Fine TPI = Threads Per Inch

 

Further information on:

BA, BSW and BSF Drilling and Tapping DataSpanner Sizes
Wire Gauges
Casting Alloy Shrinkage Allowances
Metric to Imperial Conversion

go to http://www.vintageknowledge.co.uk/ produced by Guy Weatherall.

 

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This information was collated by several of our Members whilst rebuilding their Austin Sevens.


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