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Bike of the Month

June 2019

Sonicweld 500 Triumph T100R

By Rodd Lighthouse

My bride has made some ridiculous accusations about me, or has she? She once accused me of building a motorcycle because I had acquired a throttle cable for a specific bike. Ridiculous, right?


Some time in the 1990’s a gentleman gave my father a Sonicweld dirt track rigid frame. The gent said it was for a Triumph engine. Upon telling me of his acquisition, I was stoked. Since childhood, I have been fond of dirt trackers, especially rigid frame dirt trackers. My father raced one and I wanted to be like Dad. Seeing my excitement, Dad gave me the frame and threw in some 500 Triumph motors that he had lying around collecting dust. I immediately checked out the donor’s claim and determined that the Triumph engine wasn’t the same as the motor that was in the frame prior to receiving it. 


The project sat around for a couple of years while I came up with a plan. Approximately 2001, while working on an Indian Casino project in Coarsegold, California, I took advantage of my geographic location, and took the frame and engine cases to Valencia, California to Tri C Engineering, the company producing Trackmaster Racing Frames at the time. Tri C fabricated front engine mounting plates and rear engine mounts to fit the Triumph 500 engine into the frame. Again, the project sat around for a while.


Approximately 2004, Dad and I attended the vintage Sacramento mile to check it out and see if it was something that we wanted to do. The racing looked fun, which against our better judgement, stimulated us to build dirt trackers for the race the following year. Fortunately, the vintage Sacramento did not take place the following year because I did not get the bike completed in time. I did however continue working on getting the bike together in hopes of eventually getting to race it.


I set about putting an engine together and gathering parts. Hot cams were ordered from Megacycle and high compression pistons were purchased from a local shop. Heavy-duty valve springs, new valves,  and new clutch plates were also purchased. Thirty millimeter Amal carbs from a modern 750 Triumph were acquired through a want ad and rebuilt. Cylinders were bored and cylinder head was given a fresh valve job. Dad worked his magic on the ports and built manifolds to mount the carbs. A special friction reducing coating was applied to the pistons by Swain Tech Coatings, as well as a heat emitting coating to the cylinder and cylinder head. New bearings, gaskets and seals completed the engine work.


In addition to the engine, a significant amount of time was spent sourcing chassis parts such as Barnes spool hubs, shouldered aluminum rims, stainless spokes, Goodyear dirt track tires, rear sprocket/s, solo seat, pillion pad, aluminum rear fender, and Ceriani forks. I wanted the bike to look like a legitimate dirt tracker from the brakeless era of dirt track racing, pre-1969. Engine and chassis parts were cleaned up, painted, polished, and plated, prior to assembly. 


Starting with a Sonicweld frame and an assortment of 500 Triumph engines, I was able to build one of my favorite motorcycles, a Sonicweld 500 Triumph. As it turns out, my wife’s accusation wasn’t so ridiculous after all.


In 2011 I finally got my chance to ride the Triumph on the Sacramento mile. The Triumph ran good and although the mile was intimidating, I got much faster throughout the day and ended up getting a third place finish. 

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