View source for AJS V4

{{Short description|Racing motorcycle}}
{{Use dmy dates|date=February 2018}}
{{Use British English|date=February 2018}}
[[File:1939_AJS_Water-Cooled_V4_Racer.jpg|thumb|upright=1.35|1939 AJS V4 racer restored by [[Sammy Miller Motorcycle Museum|the museum]] owned by [[Sammy Miller]] at the 2017 Stafford Classic Motorcycle Show]]
The '''AJS V4''' (1935 – 1939) started out as a prototype air-cooled V4 road bike, but became a water-cooled and supercharged racing bike.

==The 1935 Olympia Show bike==
In 1935, at the Olympia Show, the Bert Collier designed air-cooled 495cc sohc AJS 50° V4 was first displayed. It was a fully equipped road going version, which did not make it into production. This first version used a common crankcase with four individual cast iron cylinders and separate alloy heads, with exposed hairpin valve springs, and a 180° crankshaft with forked conrods. There was a central carburettor for each pair of cylinders, and fore and aft exhausts. The single overhead camshafts were chain driven. It had chain primary drive in an oil bath primary chain-case, and a [[wet clutch]]. It was stated by [[AJS]] at the time that there would be the option of replacing the forward mounted chain driven dynamo with a [[supercharger]]. The AJS used a rigid frame with girder forks.<ref name="classic">Title: ''Classic Racer'' magazine, Issue: 121, Article: Ahead of the Game, Subtitle: Supercharged V4 AJS on test, Pages: 34 - 40, Publisher: Mortons Media Group (Horncastle, Lincolnshire UK), {{ISSN|1470-4463}}</ref>

==The 1936 racer==
In the spring of 1936 a new racing version with alloy barrels appeared at [[Brooklands]] for testing, wearing a Zoller supercharger, driven at half engine speed, and fed by a single [[Amal TT]] carburettor. The [[English Racing Automobiles|ERA]] GP cars of the time used a larger Zoller supercharger. It made {{convert|51.5|bhp|abbr=on}} at 6000&nbsp;rpm. All exhaust ports now faced forward, and a branched inlet manifold fed the engine with 8 psi (0,55 bar) of boost. The engine was now mounted in the same frame as the 500&nbsp;cc OHC single TT racers, and used a four-speed [[Burman and Sons Ltd|Burman]] gearbox with a dry clutch.<ref name="classic"/>

In 1936 [[Harold Daniell]] and George Rowley rode the AJS supercharged V4s in the [[1936 Isle of Man TT|Isle of Man Senior TT]], but despite its high top speed, it lacked acceleration. Both riders retired due to mechanical problems.<ref name="classic"/>

==The 1938 racer==
Considerable work must have been done at the new AMC race shop, because the next version did not appear until 1938 and, when it did, it had a plunger rear suspension, better brakes, revised and lighter induction manifold, and raised compression. The engine had been mounted further back in the frame to improve rear cylinder cooling. A R (Bob) Foster rode one in the 1938 Senior Isle of Man TT, but it retired, from overheating, after only two laps.<ref name="classic"/>

==The water-cooled 1939 AJS V4 racer==

Where other companies might have cut their losses at this point, [[Associated Motorcycles|AMC]] did not. They commissioned Matt Wright, former [[New Imperial Motors Ltd|New Imperial]] designer, to do a complete redesign.

The result was a water-cooled version with barrels and cylinder heads cast in pairs, and fitted with enclosed valves. All exhaust ports now faced rearwards. Initially a [[Thermosiphon|thermo siphon]] design with a radiator on each side of the front frame downtubes, an impeller type water pump was soon added to the left side of the crankshaft to further aid cooling. [[Supercharger]] boost was reduced to 6 psi (0,4 bar). Instead of the previous pressure lubrication, oil was now added to the fuel. The new duplex frame had integral rear plunger suspension housings, and the Webb-type girder forks were now graced with a deep finned alloy {{convert|8|in|mm|adj=on}} TLS front brake. The bike used a {{convert|21|in|mm|adj=on}} front tyre, and a {{convert|19|in|mm|adj=on}} rear. It had a six imperial gallon (27 L) fuel tank.<ref name="classic"/>

In May 1939 A R (Bob) Foster entered one in the [[North West 200]], but it flooded on the start line.

At the [[1939 Isle of Man TT|1939]]  Isle of Man TT two bikes, ridden by Walter Rusk and A R (Bob) Foster, were 11th and 13th in the [[Senior TT]] and the supercharged  [[BMW Motorrad|BMW]] [[BMW Type 255 Kompressor|492cc Type 255 Kompressor]] of [[Georg Meier]] and Jock M West took the first two places. Though capable of high speeds, the AJS V4s did not handle well, and blew head gaskets in practice.<ref name="classic"/>

At the 1939 [[Ulster Grand Prix|Ulster GP]], the last GP before the War, the two bikes led from the start against [[Norton (motorcycle)|Nortons]] and a supercharged four-cylinder [[Gilera]], but halfway round the first of the {{convert|14|mi|km|adj=on}} laps, already timed at {{convert|135|mi/h|km/h|abbr=on}} on one section, A R (Bob) Foster retired with plug trouble. Rusk completed the first lap at a record breaking average of {{convert|100.03|mi/h|km/h|abbr=on}} and a lead of 34 seconds. On the third lap a fork link broke forcing retirement.<ref name="classic"/>  It is believed that this was caused by mistaken fitment of a 7R fork link instead of the stronger V4 part during servicing.

In 1939 the {{convert|405|lb|abbr=on}}. dry sump V4 was the first bike to lap the Ulster Grand Prix course at over {{convert|100|mi/h|km/h|abbr=on}}. Then World War II intervened.<ref>{{cite web |last1=Hilliard |first1=Frank |title=The Sammy Miller Museum |url=http://www.motorcycle.com/mo/mcfrank/sammymuseum.html |website=Motorcycle Online |accessdate=25 October 2006 |archiveurl=https://web.archive.org/web/20061205061206/http://www.motorcycle.com/mo/mcfrank/sammymuseum.html |archivedate=5 December 2006 |date=1997}}</ref>

In June 1946, the AJS V4 finally won, at [[Chimay]] in [[Belgium]], ridden by the same Jock M West who had defeated the AJS on a [[BMW motorcycles|BMW]] in the TT before the War, and was now AJS Sales Manager. Walter Rusk did not survive the War, and Jock's mount was the bike Rusk had ridden. A week later at [[Albi]], France, Jock West was in the lead when a crankpin seized and locked. When [[Sammy Miller]] acquired the engine from Jock West thirty years later to rebuild the AJS V4 for his museum, he found the crankpin still seized.<ref name="classic"/>

The engine used by Walter Rusk in the Ulster GP, with 7.9:1 compression and 16.5&nbsp;lbf/in<sup>2</sup> (114 kPa) of boost, made {{convert|55|bhp|abbr=on}} at 7200&nbsp;rpm on a dynamometer.

AJS was already developing another supercharged engine, the [[AJS Porcupine]], but, three months after the Albi race, the [[Fédération Internationale de Motocyclisme|FIM]] banned all forms of forced induction for motorcycle racing.

''[[Motor Cycle News]]'' reported that the 'Sammy Miller' machine was refurbished and ran during August, 1979 "for the first time since it seized in Albi, France in 1946".<ref>''[[Motor Cycle News]]'' 15 August 1979, p.17 ''V-four fire-up!''. Accessed and added 30 September 2015</ref>

==References==
{{Reflist}}

==External links==
*[http://thekneeslider.com/archives/2006/10/31/motorcycle-builders-air-cooled-ajs-v4-engine/ Replica of Olympia Show AJS V4]
*[http://www.kunis.nl/bikesuk/index.html Kunis.nl AJS V4]

[[Category:Vintage vehicles]]
[[Category:AJS motorcycles|V4]]
[[Category:Motorcycles introduced in the 1930s]]