It’s always good to see an established builder move out of their comfort zone, and even better to see them land a king hit at the same time. I’d never have guessed this vintage-themed dirt bike was from Clay Rathburn of Atom Bomb Custom, but 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 reveals. “I think some of that influence shows up from time to time in my rigid customs.” 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.”
Somewhere along the way, the project took a turn towards 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 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.
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.”
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