Triumph 3HW

14th November 1940 was the night that the Luftwaffe launched their infamous raid on Coventry, which military intelligence had forewarning of but were powerless to prevent without giving away the fact that Alan Turing had cracked the German Enigma codes at Bletchley. Or that's what I believed, but having read up on it just now it appears that is a misinterpretation of facts first made available in the late 60s or early 70s.

Along with many others, the Triumph factory was destroyed. With it went the 350cc 3TW, a primary product in Triumph's war effort.

An old foundry in Warwick was converted into a machine shop and production of Army service parts began. It was an uphill task in the very basic workshops but work progressed and by June 1941 complete machines were again rolling off the factory floor.

By then, Edward Turner had  moved to BSA. The new machines in production had OHV 350cc power plants and were based on the pre-war 3H, and renamed 3HW. The only major difference was that whereas the 3H and Tiger 80 had separate alloy rocker boxes, the 3HW rocker boxes were cast integrally with the head.

The 3HW was employed with forces in North Africa, India and Greece. The Greek Army used these machines from 1942-1952.

A major problem with 3HW machines in N.Africa and India was the lack of an air cleaner, and the dust played havoc. A couple of thousand miles was about the limit before major servicing was required. This same problem was encountered by the G3/L Matchless.

It was an extraordinary oversight on the part of both the builders and the War Department.



Type__________________________O.H.V. Single Cylinder

Cubic Capacity_______________________________343cc.

Petrol Tank Capacity_____________________3.1/8 Gallons

Oil Tank Capacity_________________________3/4 Gallons

Oil in Chaincase_____________________________3/4 Pint

Bore______________________________________70 mm.

Stroke_____________________________________89 mm.

Tappet Clearance (Cold)_____________Inlet______1 Thous.

______________________________Exhaust_____1 Thous.

Lubrication_______________________________Dry sump.

Gear Ratios






Con. Rod--Side play_______________________.003"-.015"

_________Big-end diameter____________1.4620"-1.4623"

Crankpin-Bearing diameter_______________.9620"-.9617"

Shafts And Tappets

Timing Shaft diameter (bearing position)_____.9995"-1.000"

Drive Shaft diameter (bearing positions)_____.9995"-1.000"

Camshaft Bush diameter (internal)_________.5610"-.5620"

Idler Gear Bush diameter (internal)_________.4995"-.5005"

Tappet Guide diameter (internal)___________.3740"-.3750"

Tappet diameter (external)________________.7495"-.7500"

Piston And Barrel

Bore diameter________________________2.7555"-2.7560"

Max. permissible wear before reboring______________.008"

Piston Clearance-Top of Skirt_______________.008"-.0085"

_____________Bottom of Skirt_____________.004"-.0045"

Piston Rings-Gap_________________________.010"-.014"

____Groove Clearance, Compression_________.001"-.003"

____Groove Clearance, Scraper____________.0005"-.0025"


Valve Guide diameter (internal)_____________.3120"-.3130"

Valve Stem diameter-Inlet_________________.3095"-.3100"


Valve Seat Angle_________________________________45

Tappet Clearance________________________________Nil

Rocker Bush diameter (internal)____________.5620"-5630"

Rocker Spindle diameter__________________.5605"-.5610"

Timing-Inlet Opens,B.T.C.______________________47.1/2"

______Inlet Closes, A.B.C.____________________68.1/2"

______Exhaust Opens, B.B.C._________________69.1/2"

______Exhaust Closes, A.T.C._________________46.1/2"


Timing, fully advanced____________________________3/8"

Contact Breaker Point Gap______________________.012"

Sparking Plug Point Gap__________________.015"-.018"

Oil Pump

Body, Scavenge diameter (internal)______.37475"-.37525"

Body, Feed diameter (internal)__________.31225"-.31275"

Amal Carburettor

Carburettor Nr:___________________MT12/AM/276AD/1J

Main Jet______________________________________150


Needle Jet____________________________________107


Clutch & Gearbox

Clutch Rod, Lost Motion_______________________1/32"

Clutch Cable, Lost Motion______________________1/16"

High Gear Bush-Layshaft diameter (internal)___.7498"-.7505"

______Mainshaft diameter (internal)_______.8115"-.8125"

Clutch Spring, Free Length______________________1.5"


Girder fork

Spindle diameter_________________________.435"-.436"

Spindle Bushes diameter (internal)____________.437"-.438"

Tyre Sizes____________________Front & Rear___3.25-19

Wheel Base_________________________________52.1/2"

Overall Length__________________________________82"

Overall Width________________________________28.1/2"

Plug Point Gap__________________________15-18 Thous.

Contact Breaker Point Gap___________________12 Thous.

NOTE. - All bush measurements are finished sizes in position where the bush is not floating.

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