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Hip To Be Square: Walt Siegl tackles the bevel Ducati

Square case Ducati bevel engine custom by Walt Siegl
The bevel era is part of Ducati folklore. The engineering prowess of Fabio Taglioni made the British bikes of the 1970s look prehistoric, and bestowed a rosy glow over the Italian motorcycle industry—just before the Big Four Japanese makers turned the superbike world on its head.

The ‘round case’ bevels are fondly remembered and sold well, but the later ‘square case’ bikes weren’t quite so popular. Designer Giorgetto Giugiaro restyled the engine covers, but most folks regarded the new look as a retrograde step.

Square case Ducati bevel engine custom by Walt Siegl
Walt Siegl is well known for his expertise with Ducatis, and for his latest build, he’s had a crack at the square case. It’s called ‘Bedeveled’ and it was a commission from Bobby Haas, the man behind the incredible Haas Moto Museum in Dallas.

“Mr. Haas let me pick the concept,” says Walt. “I chose an 80s style Ducati: I wanted to use one of the last of the glorious big Bevels, and build a racer around the square case engine.”

Square case Ducati bevel engine custom by Walt Siegl
It would be a pure race bike, with no concessions to comfort. And although most builders would probably pick the ‘round case’ Desmo engine, Walt wanted the challenge of using the later style Bevel—“to prove that one can still build a sexy machine around that engine design.”

Haas loved the idea.

Square case Ducati bevel engine custom by Walt Siegl
Bobby and his museum director traveled from Dallas to the small town of Harrisville, New Hampshire, to visit Walt in his workshop. Heads were knocked together and design ideas tossed around.

As always, Walt wanted to build a sporting machine that performs well. Although it would be part of a museum collection, the Ducati still needed the potential to win on the track.

Square case Ducati bevel engine custom by Walt Siegl
Walt’s engine man is Bruce Meyers, and he worked his magic on the 864 cc 1980 SuperSport. The cylinder heads were ported and flowed, and oversized valves and race cams were installed. The lower end was meticulously balanced and blueprinted, and there’s now an electronic ignition for easy starting.

Walt’s also upgraded the carbs to 40mm Dell’Ortos, and built a free flowing stainless exhaust system, finished in a black Jet Hot coating. Output is now between 85 and 90 hp.

Square case Ducati bevel engine custom by Walt Siegl
Meanwhile Aran, Walt’s lead technician, helped design and build a lightweight chrome-moly trellis frame. Finished in a deep red, it’s a masterpiece of minimalist engineering.

“It’s a combination of the Ducati original and my own frame design,” Walt says. “The steering neck degree is now 24, and the swingarm is 10mm shorter than stock and set at 11 degrees to make the bike more agile.” The frame is also light compared to the original, weighing only 16 pounds (7.25 kg).

Square case Ducati bevel engine custom by Walt Siegl
The bodywork was sketched out on paper, and it’s designed to be cohesive with the squareness of the Bevel engine. “We machined the principal shape for the bodywork out of blocks of urethane,” Walt says.

“Once the machining was completed, I finished all the details by hand. Molds were made out of composite, and the bodywork was laid up in carbon fiber.”

Square case Ducati bevel engine custom by Walt Siegl
Hidden behind the fairing is an aluminum stay that also holds the battery, and a simple, mechanical-driven Veglia tachometer.

To reflect the late 70s/early 80s design, Walt has chosen lightweight MV Agusta Brutale aluminum wheels to fit that style. “Careful machining was required to get the correct offset for the driveline,” he remarks. “This period also marked the end of twisty round-tube swing arms, so we built a lightweight unit out of square tubing.”

Square case Ducati bevel engine custom by Walt Siegl
Weight reduction is always a focus for Walt, as well aesthetics. So he’s opted for mono shock rear suspension (adapted from the Ducati Scrambler), an innovation that Ducati first used on the 750 F1.

For performance reasons, there’s a USD fork up front. It’s a hybrid, with Ducati Scrambler fork legs, and lowered and revalved internals. The lower tree is from a modern Ducati, but the upper tree is a custom WSM unit.

Square case Ducati bevel engine custom by Walt Siegl
The brakes are relatively simple. “Any vintage engine, no matter how many performance parts it’s stuffed with, doesn’t have the horsepower to really require dual radial calipers,” Walt points out. “So I opted for an oversized single disc with a late model Brembo caliper to slow things down.”

The paint is another visual connection to classic Ducatis: Walt’s picked the famous large metal flake that was used on Paul Smart’s original racer. Allied to the red frame and classic decals, it gives this bevel beauty even more ‘pop.’

Square case Ducati bevel engine custom by Walt Siegl
The Haas Moto Museum contains some truly extraordinary machinery, but Walt’s Ducati will easily hold its own. And maybe the oft-maligned ‘square case’ bevel will gain a few new admirers, too.

Walt Siegl | Facebook | Instagram | Images by Gregory George Moore

Square case Ducati bevel engine custom by Walt Siegl

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