Here we have something very unique. A 1949 Triumph TR5 Trophy “Square Barrel” fitted with a Bill Martin swing arm conversion. The story of the way this conversion came about can be read about in the photos above but basically Martin was the Triumph dealer in Burbank California during the 1950’s who designed a spring frame for desert racing here in So Cal. Triumph did not offer a swing arm frame until 1954, Martin started production on his in 1952. Massive success came in 1953 at the Big Bear Enduro where Vern Robison came in first at the grueling desert race aboard a Triumph Thunderbird with the Martin conversion. It was due to that victory the frame was nicknamed the “Big Bear Spring Frame”.
I acquired the bike back in January 2022 and at that time had no plan of action for it. It was in a very sorry state, it had sat for the last 60 years outside. Later in the year I was approached by the guys who put on the Born Free custom motorcycle show who asked me to be one of the invited builders for the 2023 show. As the years have gone on the show has been expanding the range of custom bikes on display and they now have sections for Desert Sleds and Pre Unit Triumphs so I thought this would be an ideal candidate for the show. Only problem was that I only had 8 months to complete the build, which for me is not a great amount of time! Anyways, I got the job done and the bike was on the grass at the show. It even won an award.
The 1949 Triumph TR5 as well as 1950 models were fitted with the legendary Square Barrel top ends. Originally the cylinder and head were part of a generator set supplied by Triumph to the RAF for providing power to the Lancaster bombers during world war 2. After the war the surplus of top end sets were then used on the Trophy TR5 and Grand Prix racers. The very first all alloy Triumph engine was born.
I performed a complete restoration as it was too far gone to even consider a preservation or patina build. No stoned was left unturned. Surprisingly enough I was able to save most of the cycle parts. After vapor blasting the aluminum parts all cleaned up very nicely. Lots of repairs were made to the cycle parts which were then sprayed black, no powder on this build. As you can see the exhaust ports are not splayed but come out straight, a pair of custom pipes were fabricated to suit. Bill Martin used shock absorbers from the front of a Chrysler auto, funny how similar the later Triumph units looked. A vintage Bates solo seat and Wassell ribbed fender give the bike some neat sweeping lines. I was able to get my hands on a pair of new old stock Avon Trials and Sports tires, both 19″. Some parts were challenging to locate as the TR5 used many unique parts not shared by the other twins. Sparks provided by a manual advance BTH Magneto, this was completely overhauled. A brand new 276 Amal Carburetor has been fitted. The Triumph logo on the fuel tank was hand painted, it is not a decal. At the end of the day I am well pleased with how things finished up. Black and Ivory in my opinion is a great color combination, I have a 1958 Tiger 110 in those colors that also remind me of the keys on a grand piano. Please enjoy the photo stream above and thanks for looking.