JAP-TRIUMPH RECORD HOLDER
No special fuels, multi-man team or cunning tricks – this Jap-triumph sprinter heads its class with good old-fashioned engineering
No fancy gubbins, no big-bucks team – this is how to go seriously fast the old-fashioned way
Standing out at the last-ever bike meeting held at Shakespeare County Raceway, this 500cc Jap-triumph sprinter caught the attention due to its functional simplicity. A serious contender and hard to beat in the 500cc Vintage class, it turns standing-start quarter miles in the 12-second bracket and holds the class record with 12.45s at 108mph. Yet this straightliner has no supercharger, no slider clutch, doesn’t drink nitro-methane, has a skinny 4.00 rear tyre and doesn’t need a team to fire it up.
Between runs, when others were fettling more elaborate and unpredictable machinery, its owner John Young parked the bike up and enjoyed a cuppa with his partner Maggs.
An expert-level motocross rider in the early 1970s, John got to know JAPS when he tried grasstracking. He took up sidecar trials in his mid-50s and, with son Paul as passenger on an Ariel HT5 outfit, won seven Pre-’65 championships. He retired from his job as a car mechanic in 2015 at the age of 70, but rather than put his feet up he does a bit of bike sport. In recent years, he’s piloted a Yamaha Xt500-powered outfit in long-distance trials with friend John Hind, topping their class in the Land’s End Trial, the Exeter Trial and the Edinburgh Trial. And, of course, he races this special single.
Built in 2003, the bike conforms to Vintage (pre-1946) rules, being based on a 1936 Triumph Tiger 70 frame and girder front forks. The engine is a true classic, the single-cylinder 497cc (80 x 99mm) JAP unit that dominated speedway from the 1930s to the 1960s. The pre-war ‘five-stud’ type, with five cylinder and head through-bolts introduced in 1935 to beef-up JAP’S original four-stud speedway motor, it’s a pure racing engine with the main bearings, big-end and rocker bearings all caged-roller
units. Pushrods bear directly on roller-type cam followers, actuated by what John calls ‘good cams’. Non-standard features are the modern Carrillo steel conrod on a Jawa big-end assembly, and also the crankcases. “Originally these engines had a magnesium crankcase, which tends to split below the barrel flange on the drive side,” John explains. “You can weld them up but they only last one weekend, so I had four new sets made in aluminium alloy.”
The cast iron cylinder and head have shallow finning sufficient for short dashes at full power on cool-running alcohol fuels. Carburation is by a brass-bodied Amal with an alloy intake stack and remote float chamber (John quotes the main jet size as “about 1025, or an eightinch drill bit”). Sparks are provided courtesy of a BTH magneto.
Lubrication is the original total loss, an external Pilgrim pump fetching oil from a tank under the minimal seat which collects in a chamber beside the lower crankcase after circulation (it would originally drip out). A tube guides it to a catch bottle behind the gearbox, and to prevent track
contamination John discreetly slips a panty liner into a tray under the sump.
The unit is famous for strong bottomend torque and, with a compression ratio of 13.5:1, John estimates output at close to 50bhp. He has the engine ‘looked at’ by octogenarian JAP specialist Gerry Goodwin.
The four-speed gearbox is the 1930s-1940s Norton type, nicknamed the ‘doll’s head ’box’ because of the selector cover’s shape, and has split-second-saving close ratios. The three-spring dry clutch is also Norton, and an important part of the bike’s speed. “Getting a good time is all in the take-off,” John says. “On a grippy surface you can’t just drop the clutch, as
the front wheel will come up and chances are you’ll end up on your backside. It’s something that takes practice – you couldn’t just get on that bike and do it.”
In a meeting interrupted by rain, John didn’t break any records but ran respectable upper 12s with 104mph terminal speeds. John was also riding despite a hand injury. The JAP can be push-started, but a couple of months earlier at the Montlhéry Vintage Revival he borrowed a foot-operated electric starter. In the heat of the moment, part of his right forefinger was severed when it got caught between the final drive chain and the rear wheel sprocket.
Who says you have to be sensible after you’ve entered retirement?
‘THE ENGINE IS FAMOUS FOR BOTTOM-END TORQUE’