At one end of the custom bike spectrum you have the drag bike. Stripped of all excess weight, optimized for power, and clad only in a patchwork body tattoo of sponsorship stickers and bits of paint, motorcycles tailored to the drag strip are as extreme a custom ride as you'll see anywhere in the motorcycle universe. At the other end of said spectrum you've got your extreme show bike. Slathered in artwork and raised on bondo and outrageous bodywork, they're made for catching eyes instead of burning rubber. Both styles weren't meant for street riding although they were built to compete. In the 1970s, the digger bike explored the huge gulf separating the extremes.
Arlen Ness was the biggest proponent of the digger bike back in the day. Where he and others drew inspiration for what's become the digger style is a mixed bag, though. Some attribute the digger's origin to the Frisco style, others say a day at the drags flipped a switch that gave Ness the idea. History is rarely as cut-and-dried as all that. Myself, I believe it was most likely a combination of the two. Arlen was as deeply involved with the Frisco bikes as you can get and there's definitely drag racer look to your typical digger machine (long and low profile, mid- or rear-mount foot controls, extensive motor mods, you get the idea). Like their Frisco chopper cousins, diggers were narrow. That's a key difference setting them apart from the wide tires you'd see on a drag racer.
What is damn true is that by 1976 magazines like Street Chopper had more and more fully realized digger bikes on their covers. Very long and low, digger chops were svelte, with coffin or prism gas tanks teamed with girder front ends, wild paint, and in many cases, lots of engraving on the cases and rocker covers. Combined with superchargers, turbo kits, racing carburetors, and motors foreign and domestic, these were the collective symptoms of digger fever. To get the long and low look for the digger, they were usually built with low gooseneck frames and would have a big rake to the front fork. The frames also had chopped backbones so that they could be lengthened for the long look. Lastly, there's that curious name: digger. Back then, the dragsters that inspired these bikes were also called diggers.
Although the digger era faded out by the mid-1980s as riders turned toward fatter bikes, the digger influence never truly went away. Look closely at a pro street chopper and you'll still see a little bit of its digger ancestors in it.
Theory of Evolution
The pieces for what would become the digger style were largely in place by 1971. Street Chopper's March `71 cover showcased a long chop with a very early coffin/prism tank on a narrow rigid frame. Over the next five years, the digger evolved in bits and pieces. Just look at the bikes on the covers below.
Year of the Digger
Over the next year and a half, Street Chopper featured so many of the bikes you could call 1977 The Year of the Digger. Almost every cover had one on them. It was right around this time that the Hamsters MC was growing in leaps and bounds, thanks to bike builders like Arlen Ness, Dave Perewitz, Donnie Smith, and Barry Cooney. Incidentally, their interactions at events like Daytona Bike Week and the Sturgis Rally spread the digger vibe from the West Coast all the way to the East, with Dave Perewitz drawing on the style for some of his most famous bikes of the decade.
Chopper folklore dictates that Arlen Ness came up with his first Sportster-based digger after he attended a drag racing event in the early 1970s. Likewise, John Harmon created his own take on the digger around 1976. Sporting his famous front ends and badass high displacement motors, they were some of the coolest examples of the breed found anywhere. Eventually, the Digger style led to John Harman building his own proprietary V-twin in ’81. It was a limited-production long-block street engine that included cases, barrels, and heads and came ready to assemble in either 116- or 120-inch configurations. The cases were 356-T6 aluminum with seamless mild steel inserts locked into the casting. John used a stock Harley stroke and crank. The deck was 9/16 inch taller than a stock Harley motor, and the right-hand case was 3/8 inch wider. Its stock connecting rods required Chevy pin bushings to accept the larger-diameter wrist pin. Customers had the option of using a stock H-D crankcase assembly (for the rest of it) or a 4-inch S&S version. The lower end was machined to run stock Harley elements, but John recommended a pretty wild cam for his big, bad mill. Its barrels featured large cooling fins and 4-3/8-inch bore. Also, the cylinders had O-ring gaskets at the head instead of the standard stock H-D used at the time. The heads were set up for dual 40mm carbs. John ran an exhaust that was 2 inches in diameter and required a special header. It retailed for $2,250. Drag versions were also available, up to 143 ci.
Tanks for the Memories
The tanks and paint jobs were as wild as the rest of the digger bikes. Body work was molded to flawlessness. Tank designs varied but were mostly of the angular persuasion (coffin or prism). New paint patterns and colors emerged making the bikes look even wilder. Day-Glo, fluorescent, pearl, and metal-flake iterations all made their way into the digger movement.