Polychromatic Blue Thunderbird Classical Gas and Sharna

WHEN Mason Williams wrote his great acoustic tune, Classical Gas, I can’t say whether he was thinking about riding a motorcycle, but there ain’t nothin’ like throwing a leg over a classic bike, fettling the throttle and having the tune of a fine engine singing in your ear, good vibrations buzzing through your hands, wind in your face and bugs in your teeth… well, maybe not the bugs… but it sure is a gas!

This is not a new experience, it’s been going on since motorcycles were first conceived and anybody who has experienced it, get’s ‘it’. What’s more, it doesn’t matter what you’re riding as long as you’re riding; after all, it’s about ‘it’ rather than how ‘it’ is delivered.

However, there’s nothing quite like having the right delivery method and this fine piece of English engineering can certainly be considered the right tool for the job. Back in the day, 500 cc was the ‘big bike’ norm so Triumph’s decision to increase engine capacity to 650 cc for the Thunderbird gave them a distinct advantage over their rivals and the Thunderbird instantly became one of the fastest motorcycles available for that era.

The logical path to more power was to increase overall engine capacity, according to Triumph’s engineering guru, Edward Turner (formerly with Ariel until starting at Coventry in 1935). A bore of 71 mm and a stroke of 82 mm created a capacity of 649 cc, so without altering anything else, the tried and true Triumph donk became a powerhouse without the need of a total redesign or having to break the bank; and by retaining the pre-unit construction method, which was popular at the time, meant a quick and reasonably easy introduction of a new model to the marketplace.

The engine is essentially a 500 with a new top-end and crankshaft, same barrel with a larger bore, a redesigned head with more fins and a copper head gasket, but the same valve gear. 

To cope with the added power, the Thunderbird got a new stronger three-piece pressed-together crankshaft and the engine cases were beefed up around the main bearings. The oil pump’s capacity was increased by 20 percent. 

The gearbox was strengthened with larger pinions, a greater number of teeth (finer pitch) and improved shift forks; and the clutch received an extra plate (now five drive and six driven). 

A lower compression ratio of 7.1:1 was used in Britain because their fuel was crap, but export models got a higher 8.5:1 compression boost, and with 34 hp @ 6500 RPM, the Thunderbird was capable of 100-plus mph.

This particular Thunderbird has the hi-comp engine, but Clive, it’s owner, has only been brave enough to push it to a bit over 80 mph… and who can blame him with local NSW road conditions being so ordinary!

Speaking of road conditions, a rigid frame won’t do your back any favours, but keeping the rigid frame was Triumph’s way of saving on R&D costs while still setting a higher benchmark for the competition. 

To combat the spine compressing comfort, Mr Turner came up with the sprung hub by placing springs radially between the rear axle & the hub/spokes/wheel. Theoretically, the springs would absorb the bumps while keeping everything in line; the problem being that, play in the system resulted in uncontrolled wheel movement and erratic handling. But it was better than nothing and remained in service until the swing-arm came out in 1954.

According to my research, the 1950 model came out in Thunder Blue, a blue/grey colour, where this particular bike is closer to the 1951 model Polychromatic Blue, but apart from that, the two models are essentially identical. 

While Clive’s bike also has the hubs painted black rather than being colour matched to the rest of the bike, as per original, it also has much of the hardware replaced with more durable stainless-steel nuts and bolts keeping this bike in immaculate shape.

But don’t be fooled by the pristine appearance of this Trumpy. Clive takes it out for spin every now and again to attend shows and events (or to magazine photo shoots) but it’s no trailer queen—he rides it wherever he takes it just so he can taste those fresh bugs! 

Words: JT of Crotch Rocket Motorcycles. Photos:- iShootPix

Sharna Jean

I AM currently based in Newcastle New South Wales. I took on modelling as a hobby about five years ago; on top of that, I am currently completing my Fine Arts Degree at university which is where I gained my initial interest in photography. 

I also have a huge passion for anything related to pin-up, especially the cars and bikes. I enjoy the whole scene of being glamorous, but I also don’t mind helping out in the shed. 

I mainly shoot pin-up and alternative projects, and this shoot for Ozbike magazine was my first with a motorbike. It was so much fun and a bit of a challenge, which I loved.