Vintage Warhorse: 1973 BSA B50MX

BSA B50MX

“This bike is like a owning a horse…. Whisper softly to her and she might get you home.”

The BSA B50MX was the motocross version of the beloved B50, which would be the last of the big unit-construction singles to come from the Birmingham Small Arms company before their demise in 1973. That gives the MX quite a distinction:

“The BSA B50 MX was the final competition motorcycle ever built by BSA, a proud British motorcycle manufacturer who had built a staggering number of race winning motorcycles over its decades long history.” —Silodrome

BSA B50MX

Built for off-road competition, the B50 MX version was stripped down to 300 pounds, with BSA engineers using as much alloy as possible to lighten the machine. The frame was a tubular steel duplex cradle design, which held the oil in the top tube, and the engine was a 499cc OHV unit-construction single that sent 34 horsepower through a 4-speed gearbox.

BSA B50MX
Photo credit: @lostandenjoy

While the bike struggled to compete against the new breed of lightweight European two-strokes, the B50MX remains a sought-after vintage dirt bike that harks back to the golden age of British big-single off-roaders.

BSA B50MX
Plated for the street!

Our new friend Stephan J. Bridges (@xsbridgesx) is a dual US-UK citizen who found his way to British motorcycles through another of the United Kingdom’s storied products: whisky.  In 2016, Stephan inherited the whisky collection of his late father, a military veteran, and began posting reviews on his Whisky Spy page, where he crossed paths like-thinking motorcycle enthusiasts and soon took the step of buying his first bike, a Triumph Bonneville T120.

“My English heritage and dual US-UK citizenship was and remains the dominant influence on my motorcycle riding.”

BSA B50MX

Within the first few years of riding, Stephan had joined the 59 Club and Brit Iron Rebels, putting nearly 50,000 miles of street riding under his belt, but the desert dirt beckoned.

“I brought my bikes to BA Moto in Long Beach for service and parts where I met Nate Hudson who runs the shop. I had always envied their vintage Triumph dirt bikes and the fun they appeared to have racing them at Glen Helen.”

BSA B50MX
Photo credit: @lostandenjoy

Soon, he was on the hunt for a machine of his own, and in August of last year, he bought this 1973 BSA B50MX from his friend Jeff Sedlik, who was trying to trim down his stable of two-wheeled animals. It would be Stephan’s first vintage bike, first dirt bike, first race bike, and the first bike he really planned to wrench on himself.

“My intention for this bike is to ride it in the Mojave and enter vintage classes for some of the longer desert races. Vintage motocross track racing has become a step along the way. It is much different than open desert racing, but if anything, it gets you out in the dirt regularly and forces you to keep your wrenches turning.”

BSA B50MX
The original find in Missoula, MT, by Stephan’s friend Jeff Sedlik.

After upgrading the bike for vintage competition — details below — Stephan began competing in American Retrocross, a vintage motocross series, which is teaching him the “prep, race, clean, repair, prep again” cycle of racing — invaluable lessons for desert racing, when he may have to fix the bike on the side of the trail, 30+ miles from his truck.

BSA B50MX

We especially love Stephan’s description of owning his BSA motocross machine:

“This bike is like a owning a horse. She is temperamental and requires considerable care and feeding. You can’t let her idle in the stable for too long. You need to get her out otherwise she can get very uncooperative. If you can get her to kick, she chomps at the bit to run. Her gallop is a little rough out of the gate but once you’ve earned her respect, she softens up and smooths out her stride. Whisper softly to her and she might get you home.”

BSA B50MX

Though it can be tough to put such a gorgeous and storied vintage machine through the punishment of competition, Stephan has received some sound advice from the Southern California off-road community:

“Some of the best advice I had been given so far is, just shrug your shoulders and remind yourself it’s a race bike. This sentiment keeps things light and breezy.”

BSA B50MX

Stephan says, given the big thumper’s curmudgeonly nature, every time he gets the bike prepped, puts it on the line, and passing the checkered flag at a vintage motocross event, he feels a great sense of pride and accomplishment. But the BSA has become more than that — a way to honor and remember his father:

“Moreover, if my dad were still here, he would have enjoyed seeing me ride my motorcycles. In my own small way, this is part of my salute to him and his life. I ride with the mindset he is watching all the time and I know he would be proud.”

BSA B50MX

Below, we get the full story from Stephan himself on this British thumper, and more gorgeous shots from Jeff Coté Photography (@lostandenjoy).

BSA B50MX Vintage Motocrosser: Owner Interview

BSA B50MX

Please tell us a bit about yourself, your history with motorcycles, and your workshop.

I gave the eulogy for my dad’s memorial service in the Spring of 2016. He passed at age 80 although his Alzheimer’s had taken over a few years before. He was buried with full military honors at Miramar National Cemetery. Through a kind favor from an active colonel at the base, we were informed to “look up” as he arranged a flyover during his service. I watched the two fighter jets approach our small gathering and with tears in my eyes, one broke away from the other in a missing man formation tribute. While I watched the jet continue out of sight, my only thought was how can I honor my dad and his military and civilian accomplishments?

I acquired the contents of his whisky collection with all the good juice he was saving for special occasions. I began sipping some of it and posted images of the vintage bottles along with some Japanese whiskies I had to Instagram. A few hashtags and followers later, I launched my Whisky Spy page and started regular postings and reviews. It was a great little diversion project in honor of my dad. Soon, I started liking the vintage cars and cafe racer motorcycles showing up in my feed. I had always appreciated these machines but given no one in my family ever rode a motorcycle — I always just admired from afar.

BSA B50MX

One day scrolling through a series of classic English, German, and Italian bikes, I asked myself, “Why not me?” After explaining this to my wife and said I wanted to try getting my motorcycle license, she replied, “Yeah…why not you?” This was the fall of 2016 and by January, I had obtained my CM1 distinction and was buying my first bike, a 2017 Triumph Bonneville T120 Black. I fell in love with riding immediately and continued learning through the endless range of Southern California’s motorcycle community groups, events, and people. I did a lot of listening to everyone I met and soon started seeing their influence in my riding skills. Feeling more confident in my abilities, I added a 2016 Thruxton to my garage in May 2018.

I joined a couple Los Angeles groups, the 59 Club and the Brit Iron Rebels. I had met more great people and had even greater fun. I traveled to the Isle of Man Classic TT in 2019 and rode out on other long weekend trips. I added a lot of new friends to my circle. I brought my bikes to BA Moto in Long Beach for service and parts where I met Nate Hudson who runs the shop. I had always envied their vintage Triumph dirt bikes and the fun they appeared to have racing them at Glen Helen. I casually started looking for a banged up, Triumph roller I could acquire for cheap and to see if I could start building a vintage desert sled of my own. Locating a bike in the right condition at the right price point was harder than I thought. People tend to know what they have and most already completed some level of restoration. Bikes I came across were too nice and shiny to tear apart and thrash about in the dirt.

Jeff Sedlik, a friend from the Brit Iron Rebels, had built up a decent collection of vintage British motorcycles. The restored Norton P11 Ranger in the background of my photo is one example. His wife insisted he trim down the number of bikes and he, somewhat reluctantly, sold the B50 to me in August 2020. As is the case with most of my riding experiences, this bike prompted a continued series of firsts: first vintage bike, first kick start bike, first dirt bike, first race bike, and first bike I was really planning to wrench on. I had a lot of learning to do.

BSA B50MX

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

1973 BSA B50MX, 500cc single thumper.

BSA B50MX

Why was this bike built?

My intention for this bike is to ride it in the Mojave and enter vintage classes for some of the longer desert races. Vintage motocross track racing has become a step along the way. It is much different than open desert racing, but if anything, it gets you out in the dirt regularly and forces you to keep your wrenches turning. Never having rode MX before and learning at age 52, American Retrocross has been awesome but takes considerable time and effort to maintain the “prep, race, clean, repair, prep again” cycle every 4 to 6 weeks. Learning to work on this bike, to understand its limits and inherent weak points will prove invaluable when bad things happen and I am 30 miles away from my truck.

BSA B50MX

What was the design concept and what influenced the build?

My English heritage and dual US-UK citizenship was and remains the dominant influence on my motorcycle riding. I am a big fan of café racer, scrambler, and brat style bikes. I also really enjoy learning about the Southern California motorcycle scene and culture during the 60’s and 70’s.

Although I would be remiss not to mention my appreciation for Steve McQueen’s contributions to the sport, my interest in desert riding and vintage motocross racing may have just come from a natural inclination to ride, explore, learn, and experience more than I had been doing. By the time I got the BSA, I had well over 45,000 miles of street riding and for as long as I could remember, I had watched friends head out for weekend trips with their MX bikes. Now here I was watching my BA Moto friends wrench and race on their cool vintage Triumphs, Maicos, and Yammies and I wanted to share in it too.

I already knew this was not going to be a showcase, period correct, pageant bike. I expected it to have a fair amount of zip ties and electrical tape holding things together, just to be broken down and rebuilt again. I knew things would crack and bend, parts would fall off, and it will be a labor of love keeping it together. Some of the best advice I had been given so far is, just shrug your shoulders and remind yourself it’s a race bike. This sentiment keeps things light and breezy.

BSA B50MX

What custom work was done to the bike?

Certain components should stay period correct, but this does not mean you never improve them. An Electrex World electronic ignition kit helped streamline the whole thumper kick start debacle. A Cone Engineering shorty exhaust replaced the awkward stock dual silencers. The stock air filter contraption was swapped out and fitted with a more efficient set up. New bars with Magura levers, custom cables, and a kill switch rounded out the controls.

I waited almost six months for some HoltWorks UK custom alloy side covers and front number plate. BA Moto did a quality job fitting an SRM sump cover with drain plug under a new, modified bash plate. The BA team also whips out some good looking, chrome replaceable fenders which help when I smash them up or convert from dirt to the plated, street light kit. I am looking to shift the foot peg mounts back a couple inches and replace them with some bear traps. Unfortunately, there is little to no improvement for vintage drum brakes.

BSA B50MX
Photo credit: @lostandenjoy
Does the bike have a nickname?

We are still trying to figure out the pet names in our relationship.

BSA B50MX

Can you tell us what it’s like to ride this bike?

This bike is like a owning a horse. She is temperamental and requires considerable care and feeding. You can’t let her idle in the stable for too long. You need to get her out otherwise she can get very uncooperative. If you can get her to kick, she chomps at the bit to run. Her gallop is a little rough out of the gate but once you’ve earned her respect, she softens up and smooths out her stride. Whisper softly to her and she might get you home.

BSA B50MX

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

I was kind of proud of selling the stock exhaust silencers to a guy in Japan who paid me half of what I paid for the bike. I am proud of the tremendous help provided by Nate at BA Moto and Tim Hickerson with Century Motorcycles in San Pedro. Their advice and insight have enabled this bike to become a more consistent, somewhat predictable, dirt-worthy competitor. They have been able to alleviate a lot of insecurities about whether the bike will start or not. Unlike Triumph twins, BSA thumpers are not easy machines and so every time I get this bike prepped, put it on the line, and finish with a checkered flag at an American Retrocross event, I am proud of the accomplishment. Racing is hard.

Moreover, if my dad were still here, he would have enjoyed seeing me ride my motorcycles. In my own small way, this is part of my salute to him and his life. I ride with the mindset he is watching all the time and I know he would be proud.

BSA B50MX

Builder Thanks

Shop Experts:
Nate Hudson — @ba_moto
Tim Hickerson — @century_motorcycles

Advice Experts:
Jeff Sedlik — @jeffsedlik
Scooter Pro — @scooterphoto
Rick Doughty — @american_retrocross

Photog Expert:
Jeff Coté Photography — @lostandenjoy

Builder Profiles:
Stephan J. Bridges — @xsbridgesx & @whiskyspy

2 Comments

  1. Elam Blacktree

    Great story! More like this, please.

  2. My B50 is an Ex-Dick Mann and Jeff Smith machine. Has the Dick Mann frame mods, dead loss oiling system, pointless ignition,
    Works Performance shocks, Ceriani Forks, custom fab foot-pegs and brackets, custom chain guide, brake pedal, one off hand hammered side plates, and custom alloy tank. After many AHARMA events including the Steamboat National MX, never had a mechanical issue. I ran most events starting in 2nd gear, shifting to 3rd for most of the race. Fantastic in the mud, stellar in the hard-pack. I also ran in the 125 class on a Maico and in the 250 class on a 125cc framed mag 250 Husky. Great fun. Back in the day I spent a lot of $$$ with Rick at Vintage Iron and machine work at Gary Nixon’s old shop. If you want some pictures RGGAMMA@AOL.COM

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