Australian Triumph: 1950 TR5 Bobber

Triumph Preunit Bobber

Black Cycles x PopBang Classics build a Pre-unit Bobber… 

In the first half of the 20th century, the traditional way to build a motorcycle involved bolting together a separate engine and gearbox via a third component, a primary chain case. In 1959, the Triumph 500 twins evolved to unit construction, in which the crankcase, transmission, and gearbox were all incorporated into common cases:

“In other words, the engine package was in one piece instead of three. It was lighter, stronger, more compact, quieter, cleaner, more attractive & cheaper to produce.” —wBW

Triumph Preunit Bobber

By 1963, all Triumphs had moved to unit construction, and the older models became known as Pre-unit Triumphs. While unit construction had many advantages, many enthusiasts favor the Pre-units, which closely match the original design of Edward Turner from the 1930s.

Triumph Preunit Bobber

Recently, we heard from our friend Noel Muller of Black Cycles Australia, whose Yamaha XT500, KTM 300, and “Duconda 400” builds we’ve previously featured. He received a 70% complete Triumph Pre-unit from a customer in Sydney, Ben, with an all-alloy engine:

“Ben loves classic Triumphs but custom ‘bobber’ versions, so he gave me a rundown of how he would like the bike to be done overall. Since I am not familiar with this vintage of Triumph, I enlisted help from Justin at PopBang Classics on the Gold Coast (so in the end this has been a 50/50% collaboration of our two shops in this build)…”

Triumph Preunit Bobber

The design and fabrication work was done at Black Cycles. Noel gives us a full list below, but highlights include frame modifications, custom one-piece handlebars, leaf-spring seat with union jack upholstering, peanut tank with frenched-in speedo, stainless headers, alloy wheels with stainless spokes, and much more.

Triumph Preunit Bobber

Meanwhile, Justin at PopBang Classics handled the engine and transmission rebuild, wired the bike, applied the gold leaf to the custom custom-mixed green/grey paint, laced the wheels, and much more. Says Noel:

“A special thanks to Justin at PopBang Classics for all his help (it would have only been half the bike without his help (literally))!”

Triumph Preunit Bobber

While the bike is definitely custom, Noel and Justin worked to keep the bike as classic as possible as they brought it back to life:

“I think I’m most proud that we’ve got a 72-year-old classic back to better than new condition and ready to be enjoyed!”

Triumph Preunit Bobber

Below, we talk to Noel for more details on the build, and thanks goes out to Matty at Gold Coast Studio for the gorgeous shots.

Triumph Pre-Unit Bobber: Builder Interview

Triumph Preunit Bobber

• What’s the make, model, and year of the bike?

The bike is a 1950 Triumph pre-unit TR5 500cc.

Triumph Preunit Bobber

• Why was this bike built?

Ben from Sydney contacted me about a Triumph build (he is good friends with Simon, another Sydney customer who owns three Black Cycles builds). Ben had found a 70% complete Triumph pre-unit on the Gold Coast, which he then purchased and sent over to us to start work!

Triumph Preunit Bobber

• What was the design concept and what influenced the build?

Ben loves classic Triumphs but custom “bobber” versions, so he gave me a rundown of how he would like the bike to be done overall. Since I am not familiar with this vintage of Triumph, I enlisted help from Justin at PopBang Classics on the Gold Coast (so in the end this has been a 50/50% collaboration of our two shops in this build)…

Triumph Preunit Bobber

• What custom work was done to the bike?

The design & fabrication work was done here at Black Cycles, we definitely wanted custom but keeping close to classic as possible!

Along with a few frame mods (excess holes factory holes filled / de-burred), tank front filler, custom one-piece handlebars and risers with integrated lever perches.

Triumph Preunit Bobber

Peanut tank with frenched-in motogadget mini speedo, and micro switches in the handlebars.

Triumph Preunit Bobber

Leaf-spring seat covered in union jack upholstery.

Triumph Bobber

Knurled billet grips and pegs, brass kicker pedal, round oil tank, aftermarket upper fork covers.

Triumph Bobber

Hand-fabricated stainless steel header pipes upswept at rear, tapered mufflers, flanged alloy rims, s/s spokes, custom front fender to match the ribbed rear, s/s struts for front and rear mounting.

Kellermann atto all-in-one micro indicators/tail lights, brass fuel cap, many machined in house caps, covers, spacers etc. 4″ bates-style headlight, finned alloy cover plate under seat area, s/s top engine mount, etc.

Triumph Bobber

Justin handled the engine and gearbox rebuilds. The engine is an ALL alloy version (not as common as the cast iron head versions), he also completely wired the bike, applied the gold leaf to the custom mixed green/grey we applied here!

Triumph Bobber

Justin also supplied a lot of new and used parts needed to complete the build including electronic ignition, alternator, rims which he also laced and trued and much more. He has also tuned and run-in the fully rebuilt engine and box!

Triumph Bobber

Justin helps with wiring and paint on most of our builds, but when it comes to early Triumphs, he’s got it ALL covered for sure 👍

• Does the bike have a nickname?

Nickname: When Justin saw the bike completely assembled for the first time, he commented that it could possibly be one of Australia’s most detailed pre-units! So I jokingly refer to it as Australia’s best Triumph! 🤣

Triumph Bobber

• What it’s like to ride?

Currently Justin is riding/running in the bike as we speak.

Triumph Bobber

• Was there anything done during this build that you are particularly proud of?

I think I’m most proud that we’ve got a 72-year-old classic back to better than new condition and ready to be enjoyed!

A special thanks to Justin at PopBang Classics for all his help (it would have only been half the bike without his help (literally))!
And Matty at Gold Coast Studio for the amazing photos.

Follow the Builders

Black Cycles Australia: Facebook/BlackCyclesAustralia | @blackcyclesaustralia
PopBang Classics:  www.popbangclassics.com | @popbangclassics
Gold Coast Studio:  @GoldCoastStudio

2 Comments

  1. Splendid build, to die for.

  2. Looks great! Cool looking…but…How well does it stop???

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