Harley Enduro: XL1200 Sportster “Adventure Sport”

Jake Vintage builds a 70s enduro-style Sportster for city and trail… 

In 2020, we featured one of our favorite bikes of all time, a 1936 Norton V-Twin Special powered by a monstrous 1320cc J.A.P. V-twin from a two-man railway carriage. It was the work of the UK’s Jake Robbins, a lifelong motorcyclist who was already buying, selling, and building specials in his teens:

“Started riding worn-out mopeds off-road at nine years old, started spannering my own bikes with the help of my older brothers…began to buy and sell motorcycles in my teens. Left school and went to work for a local classic bike workshop, started to build specials from wrecked bikes.”

In 2005, he started Jake Robbins Vintage Engineering — aka Jake Vintage — specializing in early cast lug frame repairs and girder forks. Jake’s son William — an accomplished welder, lathe, and mill operator — joined the company at 16, and the father/son duo have been expanding their services in recent years, scratching-building custom specials and vintage replicas for customers.

The bike you see here began life as a 1990 Harley-Davidson XL1200 Sportster, an early Evo model with the four-speed transmission, chain drive, and hard-mounted engine. The owner said the bike had been sitting under cover for a while — actually for a decade, as Jake would later learn! And he was wanting a custom build that would meet a few criteria:

• Able to fit a 6’4″ rider
• Capable as a daily rider
• Somewhat comfortable
• Tame enough for London
• Capable of some trail riding

Jake says it was tall order — especially given the budget they discussed — but he was interested in working on a Harley:

“Other than a few repairs to very early Harley frames and forks, I had never really worked on Harleys. I always kind of admired the simplicity of the Sportster motor and I’m a sucker for a V-twin. There is a lot of excess metal going on with a Harley…everything is big and steroidal in appearance. In order to achieve the lighter enduro look and performance, some serious works are needed.”

Jake details all of the work below, which was incredibly extensive. Highlights include Triumph Daytona forks, shortened/flipped KTM 990 swingarm with bespoke Hagon mono-shock, rubber-mounted custom subframe, 19/18″ spoked wheels, custom-fabbed oil tank, and handmade DT400-inspired tank built to fit the Sportster’s frame.

Jake’s son William handled the switchgear and bespoke wiring loom, among other things.  All of the hard work culminated in the best part of all:

“It’s the best bit of all of this and why we do this mad shit…the test ride. The bike’s ride is transformed, with a supple long travel rear end and the custom Hagon shock doing exactly what it should.  It feels like a modern bike as it floats effortlessly across the broken concrete industrial estate road.  The steering is precise with plenty of feedback…I’m amazed as some of the suspension setup was educated guesswork.”

Jake says he’s especially proud of how he pushed his boundaries with this build, and the fact that everything apart from the wheel build and seat cover was done in-house. Below, he gives us the full rundown of this street tracker / enduro build, and we share more gorgeous shots from photographer Gary Margerum (@garymaregrum).

In the Builder’s Words…

Enter Peter and his rather shabby 1990 Harley XL1200: “It’s been under cover for a while, how much do you think to build me a 70s style enduro?  It needs to fit my 6ft 4 inch frame, be capable of being an everyday rider, have some comfort, behave on the streets of London, and take a bit of trail riding…” A tall order indeed, especially with the budget discussed…

A meeting is done, ideas and drawings exchanged, and the bike is delivered just after the first lockdown. The donor is a 1990 XL1200 four-speed in stock trim with some light mods, mostly piled in a cardboard box that was delivered with it — including a very nice original bright orange Yamaha DT400 petrol tank.

Other than a few repairs to very early Harley frames and forks, I had never really worked on Harleys. I always kind of admired the simplicity of the Sportster motor and I’m a sucker for a V-twin. There is a lot of excess metal going on with a Harley, what can only be described as a scaffold tube rear subframe, and a skinny-looking swinging arm that turns out to weigh something similar to antimatter, an oil tank made from folded iron, a battery man enough to start a diesel dumper — everything is big and steroidal in appearance. In order to achieve the lighter enduro look and performance, some serious works are needed.

I spend a great deal of time working on veteran, vintage, and classic bikes, but my motorcycle tastes are very broad and I see parts of motorcycles that have design and engineering excellence hiding on bikes that perhaps they don’t suit or would look better elsewhere. Take the forks from the Hinckley Triumph Daytona and Speed Triple — they are quality old-school right way uppers but with incredible brutal machining and butch yokes…secondhand units a-plenty and priced well — the perfect upgrade for this Harley enduro? I didn’t want to go long upside down forks from a motocrosser, as that would be too simple and possibly set an overblown tone of build. I wanted this build to be a quite subtle, tasteful upgrade build.

I find an excellent condition set of Daytona forks complete with yokes and brake calipers in a breakers. Deal is done and the forks turn up.  I machine up a new steering stem tube to suit the Harley steering head bearings, and the forks are on.

I set about fitting the Sportster front hub. I decided to use as many parts I had to hand and the decision of using spoked wheels had already been decided to keep the 70s enduro look on point. With the Harley wheel spindle modified to suit and some spacers made the hub is in. All that is left to do is make up an adapter to fit the huge Triumph Daytona floating disc to the Sportster hub. This turned out to be easier said than done, but after tricky turning the carrier is done and the front forks and hub is complete and ready to have a nice fat alloy rim spoked on.

The rear end of the bike took some major surgery. We removed the entire super heavyweight subframe and oil tank leaving just the spine of the original frame with engine in situ. I had already taken a fancy to a KTM 990 swingarm and shock unit, as they don’t use a complicated rising rate linkage with the shock absorber mounted direct between the swingarm and main frame — again a secondhand unit is purchased. Fitting it turns into a story within itself.

The KTM swingarm arrives complete with White Power shock fitted. Immediately I realise it is way too long, and of course the chain run is on the opposite side to the KTM. There is also an issue with the swingarm pivot mount on the Harley frame — it runs so close the the clutch case there is no room to fit the chunky alloy swingarm. So, I cut off the original swingarm mount from the Harley frame and machine a new one to suit the KTM arm and spindle and weld it to the back of the Harley frame 10 mm behind the original mount to gain the clearance for the swingarm.

Now the swingarm is cut up and shortened by 95mm, and because I have flipped the swingarm upside down to give the correct offset for the chain run, I have to machine up a new lower shock mount and weld it on.  This in turn means the stock shock is now too long.  A quick call to Hagon shocks and they build me up a bespoke mono shock to suit.  The top shock mount is machined and welded into place.

With swingarm now cut down and modified, I set about designing a new rear subframe.  It has to be set much higher than the original to get the correct clearance not only for the longer travel rear suspension but also to accommodate Peter’s leggy build.  Because of the comfort build brief, I decide to rubber mount the entire unit to reduce vibration to the rider and vital components.

With the design done, I fabricate it out of some 7/8” cds for maximum strength and use some bolt-through bonded rubber bushes to reduce vibration to the riders arse.  I utilise the top shock mount bolt as the top fixing for the subframe and weld on some threaded bosses just above the swingarm pivot.

With the subframe fabricated and fitted, the next job is a replacement oil tank.  We have plenty of room behind the mono shock, so I fabricate one from aluminium and tuck it inside the frame rails for maximum protection in case this bike sees any off-road duty and to give it a sleek narrow line to the rear end to echo the 70s crossers.

Due to the bike’s multi-purpose use, Morad flangeless rims are fitted, 18” rear and 19” front.  Tyres are Michelin Anakee — despite the slightly pretentious name, they have the desired appearance and on and off road credibility, as they are designed for the most recent BMW adventure sport bikes.

With both wheels and tyres fitted, along with the rear end, it’s time to design and build the fuel tank.  So I’m looking at Maicos, Montessas, Yamaha DT’s, XT’s, TY’s, and it’s at this point I remember the Yamaha DT400 tank that came with it as a guide to the style requirements. 

The tank is too short and the tunnel is way off, so rather than cut up a perfectly good hard-to-find DT tank, I use it as a sort of template and build a replica out of aluminium — only I change the lower section of the tank so it swoops over the cylinder heads, bringing the top tube of the frame up though the tank, copying the top line of the Yam tank. 

At this point, I have to give a nod to the extremely talented metal-smith Evan Wilcox from America — he shows the inner workings of this type of sheet metal fabrication on his social media.  He is using skills and not machines to unbelievable and inspirational results.

The owner Pete is called in for a meeting and a fitting with regards to detailing, like the location of pegs and bars.  While he is sitting on the bike, we soon realise it’s about two inches too low, mostly on the front end.  To overcome this, I purchased a second used lower Triumph yoke, cut it up, weld in a two-inch machined boss, and replace the existing top yoke, allowing the front fork legs to be dropped to pick up the front end.

While he is in the shop, we talk finishes and decals, etc.  I sketch one on the petrol tank with a marker pen along the lines of some of the pictures Pete had sent through, and with a few tweaks, we decide on this very retro Yamaha-inspired design you see here.  It is scanned, cleaned up, and printed in Husqvarna orange vinyl.

Next up I fabricate a slim aluminium oil tank to be tucked inside the new subframe along with a seat base.

With the bike now built, it’s over to dealing with the detailing.  Rear brake is a Harrison six-pot front caliper from the original Sporty, refurbished and fixed onto a fabricated hanger.  A HEL brake line is mated to the original refurbished master cylinder.  The front master is another eBay find, a radial unit from a late-model Honda CBR, again mated to a HEL brake line to the original Triumph front caliper. 

Front mudguard is handmade in-house and mounted to an original 70s aluminium trials mount.  The headlamp is a flipped upside down Harley unit with a hidden mount added to the bottom yoke to keep things tidy.  It at this point I hand the build over to my son William, who mounts a set of micro Rizoma indicators, a simple Honda style switchgear, and above all bespoke wiring loom and a lithium battery to power everything up.

With the bike and budget near done, the last thing on the list is an exhaust system.  With not much money left, it’s time to get resourceful.  I had recently helped a mate clear out his unit of bike bits he had accumulated over the years. 

In amongst it, I had spied some stainless silencers from a Moto Guzzi V65 — they were bruised and battered but sound, so out with the tape, pen and grinder.  Careful use of the unscathed parts of the pipes, and they are repurposed into what you see here.

It’s at this point things get very exciting with the plumbing, wiring, and relevant liquids in place — the starter is pressed.  A very unhappy motor splutters into life with virtually no throttle control and the down pipes turning blue then red — within a few seconds it is switched off.  I give Pete the owner a call and ask if it was running okay when it was laid up?  “Yes,” he says, “but that was over ten years ago before I put it the the garden under a tarp.”

When you take on a donor bike to customise you tend to take it on face value, and as presumption is the mother of all fuck ups, here I am again, end of budget and build time with a completely transformed and as yet un-road-tested bike and begin to imagine what ten idle years has done to the inside of the motor.  Stuck rings, rusty bores, pitted valve seats?  After a quick, positive compression test, fears are put to bed and the shitty running is traced to perished manifold rubbers.

With the carburetion now sorted, it’s the best bit of all of this and why we do this mad shit…the test ride.

The bike’s ride is transformed, with a supple long travel rear end and the custom Hagon shock doing exactly what it should.  It feels like a modern bike as it floats effortlessly across the broken concrete industrial estate road.  The steering is precise with plenty of feed back…I’m amazed as some of the suspension setup was educated guesswork.

I have achieved what I wanted to do:  to take an antiquated design, add on some updated good-looking equipment, and build an extremely rideable bike.  I pushed my own personal boundaries on this one, in styling but also in engineering and fabrication, because apart from the seat cover and the wheel build, everything was done in-house.

I could keep writing on this one…big thanks to Peter who set me loose on his bike.

Photography Credit

All pictures taken by Gary Margerum (@garymaregrum).

Follow the Builder

Jake Robbins Vintage Engineering
Tel: 07986254144
Web: www.jakerobbinsvintageengineering.co.uk
Facebook: @jakevintage
Instagram: @jakevintage