The Most Beautiful Triumph Dirt Bike Ever Built

Apr. 09, 2014 By By Rick Sieman and Atom Bomb Custom/Anthony Hall Photos
Here it is, one of the best looking Triumph dirt bikes ever built.

Triumphs have always been some of the best-looking bikes on the road, especially the older ones.  And an old Triumph dirt bike – done right – can be a real eye opener.  Every once in a while, you seen one that stops you in your tracks… and this is it.

This vintage dirt bike was built by Clay Rathburn of Atom Bomb Custom, and his signature attention to detail is evident throughout.  “As long as I can remember, I’ve thought dirt bikes were some of the most beautiful motorcycles made,” Clay said. “I think some of that influence shows up from time to time in my rigid customs.”

Here’s the right side of the 750 Triumph.

So nearly two years ago, Clay started planning the frame for this bike. “Beyond ‘build a Triumph dirt bike’ there wasn’t much of a firm plan,” he admits. “I had a Yamaha front end on hand, and some shocks from a Husqvarna.”

The attention to detail is staggering. Check out the drilled skid plate.

Somewhere along the way, the project took a turn toward a serious all-out custom build. When Race Tech got involved with the suspension, Clay knew there was no turning back. “The madness took over,” he says. “One thing you don’t see very often is a full-on custom dirt bike. So I decided to go full bore on making this bike as functional and nice as I possibly could.”
The shift side of the Atom Bomb Custom bike shows the tucked-in, hand-built exhaust system.

The motor is from a 1974 Triumph Bonneville, but it’s a little big for a dirt bike. So Clay cut the front motor mount ‘triangle’ off the cases, so he could slide the engine much closer to the front of his custom-designed frame. It also meant he could build a swing arm 3.5” longer than a stock oil-in-frame Triumph, with no increase in wheelbase.
The stock Bonneville motor points the carbs outboard at a wide angle, which gets in the way on a dirt bike. “Logic would dictate switching to a single carb head … but 10-bolt single carb heads are difficult to locate, and I really wanted to keep it twin carb, so I decided to relocate the intake ports. After a three-day weekend of welding, milling and working with the die grinder, the head now has intake ports that are moved inboard about an inch and a half—and the carbs point straight back.” Everything now tucks nicely inside the frame.

Husqvarna shocks handle the rear suspension chores.

The other parts are all beautifully thought out. “I gave the rear hub to my machinist pal, Chris Morris, and asked him to make it lighter,” says Clay. “Two days later he handed me the most beautiful conical Triumph hub I’ve ever seen—with every surface turned down, and flutes cut into the area behind the sprocket. It’s just beautiful, and over a pound lighter than stock.”
Once the bike was a roller, Clay added the finishing touches. Burns Stainless supplied the handmade exhaust collector and muffler, and also engineered the pipe lengths. Rebel Gears cut a custom rear sprocket to run a 520 chain rather than the stock 530. DC Plastics custom-molded the fenders. Industrial Hard Carbon applied black carbon coating on the 43mm KYB fork legs, and Powder 365 helped powdercoat the engine. The tank is loosely patterned after a stock Triumph, but around three inches shorter and with deeper knee pockets and a rounder shape. The side panels were rolled by hand with a step roll.

The gas tank may look stock, sort of, but it’s hand built.

“Since this was a personal project I wasn’t able to work on it every day,” says Clay. “It often sat for weeks without being touched. In fact, we moved our home and shop 200 miles and finished four other motorcycles while this project was ongoing! I’d say it was an obsession worth pursuing, and one of the most accomplished off-road builds we’ve seen in a long time.”
The bike has a fully rebuilt 1974 Triumph Bonneville T140 engine, a custom-designed frame, side panels, swing arm, and fuel tank. The bike was a labor of love for Clay, as his shop specializes in “custom vintage British motorcycles built from discarded, damaged and forgotten Triumph and BSA relics.”
Here’s Clay with his jewel.

For this particular machine, Clay kicked classic choppers square in the nuts and made himself a semi-modern dirt bike from scratch with a little help from an old Triumph. It looks so well proportioned and finished from every angle that you could almost think it's a factory dirt bike, though you'd be hard pressed to figure out the exact vintage.

Don't forget to check out the Atom Bomb Custom site for more of Clay's creations at Newsletter
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