EB1222 - 1986 BMW K100
Author: Ellaspede Date Posted:4 July 2023
The BMW K100 is a classic in the world of motorcycles. With its unique design, linear engine, and German engineering, it has stood the test of time and remains a popular choice among enthusiasts.
But as we’ve found with K-series custom builds, their unique design also requires the owner to ‘go the whole way’ to make the most of the ‘flying brick’ look.
The standout feature of the K100 is of course its ‘flat’ inline-four, 987cc engine. This liquid-cooled power plant delivers smooth and consistent power throughout the rev range, providing decent performance. The frame and engine combo offers good stability and balance along with a distinctive look that sets it apart from other motorcycles of its era.
BMW has always been known for building durable motorcycles, and with proper maintenance and care, these bikes can easily cover high mileage without major issues, making them a reliable companion for long-distance touring or everyday commuting.
The K100's exposed engine, riding stability and renowned reliability are all big pluses for a custom build… however, when stripped of its fairings it’s the unconventional styling that seems to be the biggest stumbling block and in turn highest hurdle to clear when trying to achieve a clean K100 custom.
This is why you see so many ‘ok’ K100s because to get around the quirkiness requires dedication, time and money if not doing it all yourself. David, the owner of this K soon realised this and contacted us with his project.
His backstory follows: “I bought the bike at an online auction about 18 months ago. The idea was to have this as a slow project bike that I could work on but I soon realised that the bike I had in mind was better built by professionals. Not sure of the history of the bike other than the original owner was also doing some resto work prior to me getting it.”
You can see in the original photo what David is referring to, with the previous owner stripping away most of the big BMW’s bodywork and fitting some small components. Unfortunately all of these parts except for the handlebars didn’t match the build, so they were swiftly removed before the new work began.
We’ve been a fan of the Retro Rides rear suspension kits for the K100’s, but they’re quite modern looking with their CNC construction, so on this build we opted to make something similar in operation but more closely matched to the factory frame style of the bike. The rear half of the frame was removed in favour of a chromoly subframe and horizontal suspension system that was designed and bent up in house before being welded on.
A custom seat pan was fabricated with a quick release latch and now matches the new rear frame, while a steel battery box was added to house the extensive electrical components found in the K-series. A steel inner guard was also fabricated to protect the electrical box and give the under seat area a nice clean look.
Finishing off the rear fab is an extended number plate mount that will also hold the tail light and indicators. Small ‘luggage loops’ were also welded to the frame for securing a small pannier or an overnight bag for the longer excursions.
At the front, an upside-down Yamaha R1 front end was fitted with Cognito Moto triple trees and top bar mounts. The forks were sent off for refinishing and rebuilding before being slotted back in. They’re complemented by custom hub/disc spacers to accommodate the 310mm discs on the factory K100 front wheel, clamped by 4 piston Yamaha callipers on both sides that were rebuilt and are fed through braided lines. A steel front guard was shaped up and hangs off custom ‘tubular’ mounts from the bottom of the ‘upside down’ forks.
Aluminium side covers were designed and laser cut to fit in the frame triangle on each side below the seat. They feature K100 cutouts which were ‘back filled’ with steel mesh for a contrast look and to stop anything unwanted getting in.
The K100's engine, known for its reliability, had good compression and did not require a rebuild during inspection. It was removed and refinished in black, with the fins on each engine cover linished for contrast. Preventative maintenance was performed in the way of various engine seals, hoses, injectors and components being replaced or refurbished as well. A special engine infill badge featuring David’s choice of German word ‘Kopfjager’ was also made in CAD and machined from aluminium.
Apart from wiring in new electrical components, finding suitable placements for all the necessary factory parts in a customised K-series BMW is a significant undertaking. The bike now features Daytona Velona 60 gauges for critical information display, controlled through custom Ellaspede K-series switches, and with Motogadget m-blaze bar end indicators at the front and Motogadget pin indicators at the rear. A classic LSL headlight lights the way, with a neat Koso Hawkeye LED taking care of tail light duties out back. Daytona Rod D-mirror 10 mirrors are underslung for the rear visibility.
The stock K100 headers were retained but shortened, a new 4-into-1 collector made and then connected to a shortened Supertrapp muffler mounted on a custom bracket.
The fabrication continued on a new radiator overflow bottle, foot peg mounts, repairs and modifications to the centre stand as well as the usual de-tabbing and cleaning of the frame and other components. A bates style spot light now hangs off the left side (via a custom bracket), with a replacement yellow lens to assist on the foggiest of early morning rides.
A new outer disc was fitted to the rear and the brake calliper was rebuilt and repainted to ensure its working correctly. A new YSS ‘black edition’ rear shock slots into the new suspension mount to hold up the rest of the rear as well.
After completing most of the fabrication work, the bike underwent a thorough strip-down. Essential parts and components were sent off for paint, cerakote or powder coat finishes.
Shinko 712 tyres in 100/90-18 for the front and 130/90-17 for the rear were mounted on the factory K100 wheels.
The new seat was foamed up using a generous amount of high density comfort foam for the longer days in the saddle. Upholstery features premium black UV rated motorcycle vinyl, horizontally back-pleated across the top and bordered by a silver graphite stitch.
Getting to the paint, David explains his intended theme and colour choices… “The colour came from the BMW Nardo grey and I thought that this would be a nice link to the present. I wanted the bike to remain true to its German heritage and so I was keen to enhance the BMW wording somewhere on the bike, which you can see on the front guard. This also led to the Kopfjager reference on the engine side panel.”
“The original inspiration for a srambler style of bike (as opposed to a cafe racer) was the bike from the movie "The Great Escape" - hence the single side light. I knew that it would not replicate the old German bikes but that was the link to German engineering of the past. I was also posted to Germany for a while and had nothing but great memories of beer, Porsches and BMWs.”
Taking in David’s inspiration, we designed a classic colour scheme for the tank and front guard, featuring the BMW Nardo Grey with black ‘knee panels’ on the tank and a metallic navy blue border and line work across both parts for a pop of colour. The extended BMW meaning also adorns the right side of the front guard.
When it comes to K100 builds, the philosophy followed here is to go all out. The stock K100 can appear bulky and eccentric, so a half-hearted customisation attempt doesn’t usually result in a satisfying result. We think this build fully embraces the transformation, acknowledging that an impressive custom example of the K100 requires going the ‘whole hog’ and we’re glad David trusted us to help him see it through.
Now that it’s finished David said “… it’s hard to say what my favourite part of the bike is as there is a lot to take in, but the rear suspension and swing arm looks incredible.”
“I'm spoiled that I have a bike to ride to work and one for weekends. I joked that this one would probably end up inside as a feature piece but my wife quickly shut that down. Not sure exactly with this one. Might use it to travel to bike shows or as a weekender.”
David now has a super clean example of a cool custom! With the smooth power, riding stability and rad new looks we would take this thing for a weekend away any day, we’ll just have to convince David to loan us the ‘Kopfjager’ keys.
Albums we listened to during the build of this bike:
|1. TISM - Best Off
|2. Led Zeppelin - Led Zeppelin IV (Deluxe Edition)
|3. Third Eye Blind - Self Titled
Photos by AJ Moller Photography
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