AJS Stormer Main Page 

On this page you can find out where to buy vintage Stormer parts, obtain tips and information, check specifications, torque settings and contact us for technical help.

We still have tons of new Stormer parts in stock.

Some parts are New Old Stock, and some are newly manufactured.
Our GRP fuel tanks are made extra thick, from the latest ethanol resistant resin.

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We deliver parts all over the world.

Many parts are available in our on line store.

If you cannot see what you want in our store, or you need help, contact us, and we'll be happy to help and advise you.

Remembering "Fluff" Brown

NEW! Folding Kickstart levers

The AJS Y4 (Stormer) is celebrating 50 years since it's first year of production. The Y4 was inaugurated in 1968. The first private rider to score a win was Alan Arnott on Sunday 16th March 1969 at The Kiwi Club's scramble at Bulford Down, Wiltshire.
Malcolm Davis won 250cc British Championships in 1968  and again in 1970, Andy Roberton brought the Stormer home in second place.
Read the amazing story of the AJS Stormer and the people who designed, developed and raced it, as told in the words of Cliff Stevens.

 Gear Ratios, Primary Drive Ratios and Primary Chain

Model: Y4, Y4 MK,2 250 Stormer 1968 - 1974 

Standard Technical Data for MX use, without "Works Tuning"

Engine

Bore: 68mm

Stroke: 68mm

Capacity: 247cc

Compression Ratio: 11:1 

Port Timings: Exhaust: 180 deg, Transfer: 135 deg, Inlet: 152 deg.

Ignition Timing At Piston: 2.5mm (.1 ins.) At Crankshaft: 20 - 22 deg.

Contact Breaker Gap: .38mm (0.015 ins.) 

Spark Plug NGK B8ES - Champion N3 Plug 

Gap: .635mm (.025 ins.) 

Transmission 

Engine Sprocket: 20T 

Clutch Sprocket: 43T 

Gearbox Sprocket: (520) 13T 

Rear Sprocket: (520) 61T 

Gear Ratios (Close Ratio): 1st - 2.00 2nd - 1.51 3rd - 1.25 Top - 1.00

Carburetter 

The Amal Mk1 32mm "932" was fitted as standard, however we recommend fitting the Amal Mk2, 34mm for standard Stormer 250 engines and Mk2 38mm for "Works Tuned" engines. 

(Check for eligibility with your club). 

Amal 932 Settings:

Throttle valve: 3 Main Jet:

280 Needle Jet: 107 Needle position:

Middle Pilot Jet: 20

Capacities

Fuel Tank: 1Imp Gallon, 2.4 US Gallons, 9L.

Gearbox: 1pint, 20 fl oz, 

Primary Chaincase: 0.57 pint, 7.5fl oz, 210cc 

Front forks (each leg): 0.57 pint, 7.5fl oz, 210cc 

Lubricant Types (recommended)

Fuel Mix: Silkolene Casterene R40 @ 32:1

Gearbox: Silkolene Medium Weight Gear Oil,

E.P.90 Primary 

Chaincase: Silkolene Light Weight Gear Oil sae 10/40 75w or Silkolene 10w Front Fork Oil If using our red dot primary chains #27799B.

Rear Chain: Silkolene Chain Lube.

Other data

Steering Head Angle: 30 deg.

Fork Trail: 5.15ins.

Pistons Piston Skirt Diameters: 67.913mm/67.887mm (2.6738/2.6727 ins.)

Piston Clearance in bore: .076mm/.89mm (.0025/.003 ins.)

Ring Gap: .178mm/0.305mm (.007/.012 ins.)

Con-Rod length, centers: 126.97mm/127.025mm (4.999/5.001 ins.)

Small End Bush Bore:17.47mm (.675 ins.)

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Model Y5, Y50 370, 370 Stormer

1970 - 1974

Standard Technical Data for MX use without "Works Tuning"

Engine

Bore: 83mm

Stroke: 68mm

Capacity: 368cc

Compression Ratio: 11:1

Port Timings Exhaust: 180 deg, Transfer: 130 deg, Inlet: 170 deg.

Ignition Timing At Piston: 2.5mm (.1 ins.) At Crankshaft: 20 - 22 deg.

Contact Breaker Gap: .38mm (0.015 ins.)

Spark Plug NGK B8ES - Champion N3 Plug Gap: .635mm (.025 ins.)

Transmission

Factory set-up. Engine Sprocket: 24T

Clutch Sprocket: 40T

(we use Engine Sprocket: 20T

Clutch Sprocket: 43T)

Gearbox Sprocket: (520) 12T

Rear Sprocket: (520) 65T

Gear Ratios - Wide Ratio. (We use the 250 Transmission set-up and a C.R. gearbox) 1st - 2.52 2nd - 1.66 3rd - 1.25 Top - 1.00

Carburetter

The Amal Mk1 34mm "1034" was fitted as standard, however we recommend fitting the Amal Mk2, 36mm for standard Stormer 370 engines and Mk2 38mm for "Works Tuned" engines. (Check for eligibility with your club).

Amal 1034 Settings:

Throttle valve: 2.5

Main Jet: 370 - 410

Needle Jet: 108

Needle position: middle

Pilot Jet: 25

Capacities

Fuel Tank: 1Imp Gallon, 2.4 US Gallons, 9L.

Gearbox: 1pint, 20 fl oz,

Primary Chaincase: 0.57 pint, 7.5fl oz, 210cc

Front forks (each leg): 0.57 pint, 7.5fl oz, 210cc

Lubricant Types (recommended)

Fuel Mix: Silkolene Casterene R40 @ 32:1

Gearbox: Silkolene Medium Weight Gear Oil, E.P.90

Primary Chaincase: Silkolene Light Weight Gear Oil sae 10/40 75w or Silkolene 10w Front Fork Oil If using our red dot primary chains #27799B.

Rear Chain: Silkolene Chain Lube. 

Other data

Steering Head Angle: 30 deg.

Fork Trail: 5.15ins.

Pistons Piston Clearance in bore: see note

Piston length at the rear: 73mm

Ring Gap: .178mm/0.305mm (.007/.012 ins.)

Con-Rod length, centers: 26.97mm/127.025mm (4.999/5.001 ins.)

Small End Bush Bore:17.47mm (.675 ins.)

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Model Y51, 410, 410 GP, 410 Stormer
1971-1974
Standard Technical Data for MX use without "Works Tuning"

Engine 
Bore: 83mm
Stroke: 74mm
Capacity: 400cc
Compression Ratio: 11:1
Port Timings: Exhaust: 180 deg, Transfer: 130 deg, Inlet: 154 deg.
Ignition Timing At Piston: .125 ins/3.2mm At crankshaft: 20-22 deg. 
Contact Breaker Gap: .38mm (0.015 ins.)
Spark Plug NGK B8ES - Champion N3 (unless a 370 conversion, in which case a short reach plug will be used such as NGK8HS)
Plug Gap: .635mm (.025 ins.)

Transmission 
Engine Sprocket: 24T 
Clutch Sprocket: 40T 
Gearbox Sprocket: (520) 12T 
Rear Sprocket: (520) 65T 
Gear Ratios-Wide Ratio. (The C.R. gearbox may be used. See 250 data.) 1st - 2.52 2nd - 1.66 3rd - 1.25 Top - 1.00 

Carburetter
The Amal Mk1 34mm "1034" was fitted as standard, however we recommend fitting the Amal Mk2, 38mm for standard Stormer 410 engines and "Works Tuned" engines.

Amal 1034 Settings:
Throttle valve: 2.5 
Main Jet: 370 - 410 
Needle Jet: 108 
Needle position: middle 
Pilot Jet: 25 

Capacities
Fuel Tank: 1Imp Gallon, 2.4 US Gallons, 9L.
Gearbox: 1pint, 20 fl oz, 210cc 
Primary Chaincase: 0.57 pint, 7.5fl oz, 210cc 
Front forks (each leg): 0.57 pint, 7.5fl oz, 210cc

Lubricant Types (recommended)
Fuel Mix: Silkolene Casterene R40 @ 32:1
Gearbox: Silkolene Medium Weight Gear Oil, E.P.90 
Primary Chaincase: Silkolene Light Weight Gear Oil sae 10/40 75w or Silkolene 10w Front Fork Oil If using our red dot primary chains #27799B.
Rear Chain: Silkolene Chain Lube.

Other data 
Steering Head Angle: 30 deg.
Fork Trail: 5.15ins.
Pistons Piston Clearance in bore: see note
Piston length at the rear: 75mm
Ring Gap: .178mm/0.305mm (.007/.012 ins.)
Con-Rod length, centers: 139.67mm/139.725mm (5.499/5.501 ins.)
Small End Bush Bore:17.47mm (.675 ins.)
 

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Errors and omissions expected. For further hep contact us.
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How to set up, re-jet and pretty much everything else you might want to know about AMAL carburetters, download the PDF information document.