A Four Cylinder W1400? …A Midlife Update of my retro styled Z

[j.wilson]

My “W1400” has been a faithful companion to me for over 15 years now; finished in September 2010 and ridden hard ever since.
Some of you will remember the original build project that was lost to the ether; the Z650/1100 Bonneville hybrid.

She's carried me the length and breadth of England and Wales, crossed to Western Ireland on multiple occasions (those Atlantic winds and twisty coastal roads are unforgettable), and even made a spring break down to Spain for a particularly memorable adventure last year.

The bike has proven itself time and again: characterful and always puts a smile on my face with that deep four-cylinder shove and light-footed handling.

But as the years stack up, the reality of parts availability starts to creep in. Some of the refurbishment items I relied on back then, the 82mm pistons and cylinder block for example, have become obsolete.
Rather than wait for something critical to fail on a remote B-road in Wales, I decided it was time for a Midlife Update.

The goal isn't a full redesign; it's preservation with sensible upgrades, replacing wear items, addressing any age-related fatigue, improving details that have revealed themselves over thousands of miles, and ensuring the bike stays enjoyable and dependable for another decade or more.

Right now, she's in bits on the bench, engine out, frame stripped, tank off, wiring loom laid out, giving me the perfect opportunity to document the assembly process step by step, and reflect on the original concept that drove the whole project back in 2009–2010.

The Midlife Update: What's Happening Now

The philosophy remains unchanged: keep the soul of the original W1400 …classic style, effortless torque, light-footed handling, real-road usability, but refresh it thoughtfully so parts scarcity doesn't become a barrier. No radical changes; just careful maintenance and subtle improvements where time and miles have shown the way.

I'll document the rebuild here as it progresses with photos of the specific parts replaced or upgraded, any surprises and lessons learned, and reflections on what has stood the test of time. I hope you find it interesting and if anyone remembers the original build posts or has followed along over the years, I'd love to hear your thoughts or questions as we go.

She's coming back together stronger and ready for the next chapter; more miles, more adventures, and hopefully fewer worries about obsolete bits.

The W1400 was always meant to be ridden, not preserved in a garage, and this midlife update will keep her on the road where she belongs.

[r3sc]

Looking forward to this update!

[j.wilson]

.
The W650

The Kawasaki W650 (1999–2007) stands as a beautifully timeless naked motorcycle, masterfully blending the classic British style of the 1960s Triumph Bonneville with the
renowned reliability of Japanese engineering. Its very name pays homage to Kawasaki's own W-series twins from the 1960s and 1970s (W1, W2, and W3), while the bike
itself captured the spirit of retro charm without sacrificing modern usability.
What truly distinguishes the W650 is its on-road demeanor. Despite a solid kerb weight around 216kgs, the bike's geometry …..27° rake, 108 mm trail, and a 1,465 mm wheelbase,
delivers surprising lightness and sure-footedness. It inspires genuine confidence, whether carving twisty backroads, navigating town traffic, or savoring a leisurely Sunday ride.

The upright riding position is a masterclass in comfort: high, wide handlebars keep wrists relaxed, the generous, well-padded seat supports the rider's back hour after
hour, and the footpegs are positioned just right for natural posture. Miles melt away with minimal fatigue, making it an easy, engaging, and deeply relatable machine,
ideal for everyday use yet brimming with character that elevates every journey.
In essence, the W650 is a motorcycle that consistently puts a smile on your face the moment you swing a leg over it.

What's not to love?

For the more enthusiastic rider, the primary drawback has always been its modest power output.

The parallel-twin engine delivers a gentle, "put-put" character rather than outright thrust with just 48hp. This becomes especially noticeable with a pillion on board or
when attempting brisk overtakes. The successor W800 (introduced in 2011 with EFI and a larger 773 cc displacement) offered slightly more low-end torque but didn't
dramatically transform the performance equation.

The Pursuit of More Power: Engine Swap Exploration
Tuning the original engine or sourcing significant aftermarket performance parts proved challenging. The W650/W800 never achieved the massive sales volumes of rivals
like the Triumph Bonneville, so a dedicated high-performance parts ecosystem never fully materialized. The options for meaningful gains were limited.
Swapping in an entirely different engine presented its own hurdles. The real difficulty lay not in sourcing a more potent motor, but in mating it cleanly to the frame.
After evaluating options, my focus shifted to a 1970s-era frame paired with an 1980s air-cooled four-cylinder engine.

The winner: the tight, compact frame from the early Kz650 B1 (1976–1977 models), combined with the Gpz1100 A3 two-valve engine (1,089 cc, delivering around 100 plus
horsepower in period form). The ultimate incarnation of Kawasaki’s air cooled four.

This pairing promised the best of both worlds; the compact, agile and sure-footed geometry of the Kz650 frame with the muscular punch of the larger 1100 motor.

The Kz650 frame's steering geometry (27° rake, 106mm trail, 1,437mm wheelbase) aligned closely enough with the W650/W800's setup to offer comfort, practicality,
maintain the retro look, familiar handling traits, while offering a proven foundation for the engine swap. Fitment was feasible, allowing the project to prioritize styling
refinements over major chassis re-engineering.

004 Rake and Trail table.jpg (84.45 KiB) Viewed 580 times

Compare the stock W800's geometry to the Kz650's and that of the ZX1100 in the table above. Culminating in my custom hybrid (W1400): tighter proportions for quicker
steering response than the big, heavy and long ZX1100, but paired with the added grunt that transforms this hybrid into a spirited, grin-inducing retro bruiser.
This custom build preserves the soul of the W-series while addressing its key limitation;
delivering classic looks with genuine muscle.

The project got serious once I started spending money and purchased the donor parts: a classic Kz650 frame from 1978, paired with a late-model Gpz1100 air-cooled
inline-four engine (the big, torquey flagship motor from Kawasaki's early-1980s era).
Rather than chase the Gpz1100's original top-end-biased character, designed for blistering straight-line speed, I prioritized the lazy, arm-stretching midrange torque
that defines a true muscle bike.

The solution?
A substantial upgrade via a 1394cc big-bore kit.

This capacity jump (from the stock 1,089 cc) transforms the engine's power delivery: deeper low-to-mid rpm grunt for effortless roll-on acceleration, open road overtakes
without drama, and that satisfying shove in the seat that the original W650/W800 always lacked. Why settle for subtle when you can have character?

With the engine destined for serious reconditioning, I entrusted the work to Ray and Steve at Debben Performance in Ringwood, ….the Hampshire specialist in classic
Japanese performance rebuilds, restorations, and modifications. Known for their expertise with Kawasaki's older fours (including crank work, head flowing, and big-bore setups),
they handled the meticulous prep to ensure reliability under the increased displacement and stress.

Thus, the W1400 was born: a conceptual name that fuses the W-series' timeless retro silhouette with the muscular heart of a bored-out Gpz1100, all wrapped in the agile,
compact and surefooted Kz650 chassis.

The build philosophy stayed true; keep the light, agile feel of the original W while banishing the "put-put" character. With the frame's compact geometry providing the
foundation, engine fitment became the critical path -requiring the removal of the old engine mounts and precise alignment of new custom mounts, so that the engine
fits snugly between the lower frame tubes.
From there, the focus could shift to the real magic: a sympathetic re-style that honors the W650's classic lines while subtly nodding to its newfound muscle.

Once the ginder came out, there was no turning back. I had to be sure this was the right thing to do.

The goal promised to be far more than a parts-bin special. I wanted a refined retro bruiser; with comfortable upright ergonomics for all-day rides, predictable handling
on twisty lanes, and a genuine shove that makes every throttle twist rewarding.

Once complete, the W1400 would deliver grins in spades: classic style, modern usability, and torque that finally matches the bike's soul.

Let’s get butchering!

[chrisNI]

Good stuff!

[j.wilson]

W1400 or bust.

With the W1400's overall vision firmly in mind, I made a conscious decision right from the start to resist the temptation of loading the bike up with every shiny, aftermarket trick part I could find. I'd been down that road before, building motorcycles that looked spectacular on show stands but ended up as frustrating and impractical because nothing quite fitted together stylistically or worked in harmony on the road. This time had to be different.

I set myself a clear goal: a refined, rideable retro muscle bike that kept the timeless W-series soul, added the midrange torque I'd always craved, fitted me pefectly and stayed practical on real roads rather than just posing.
I also wanted an understated bike that looked like it came from a factory. Every part I bought, no matter how modest or “cheap and cheerful,” had to look like it was meant to be there.

By far the biggest challenge turned out to be the fuel tank.
Virtually every tank designed for traditional twin-cylinder retro bikes was far too narrow to compliment the wide inline-four engine and held too little fuel for anything approaching a decent riding range, especially one with a 1394cc motor that was never going to sip petrol.

My initial thought was to take an original tank and have it heavily modified to fit, but after a long conversation with Simon Parker at Parker Fabrications in Bournemouth, he convinced me there was a much better way. Instead of butchering something old, we would create a brand-new aluminium replica of a Triumph Thunderbird tank.
The Thunderbird shape already echoes the W800's classic lines but sits noticeably larger and wider, perfect for what I needed.

Simon took the donor Thunderbird tank I picked up for just £13 on eBay and used it as a male mold. He then shaped and welded aluminium sheet sections around it to form a completely custom tank. The result is lighter than steel, completely rust-proof, fully compatible with modern ethanol-blended fuels, and crucially, shaped underneath to sit cleanly on the Kz650 frame rails and mounts. If it ever gets dented in the future, repairs will also be straightforward.
It was exactly the elegant, future-proof solution I was looking for; although is was also the single most expensive part of the build.

[j.wilson]

.
Have you got an Ethanol problem?

Why is the inside of your fuel tank suddenly getting rusty?
Could it be global warming?

Rust
It is common for water to be introduced during refueling, e.g., from a contaminated station pump or underground tank.
This problem is becoming more common.

062 Rust in a tank.jpg (65.7 KiB) Viewed 407 times

The bare steel inside of an older motorcycle fuel tank will rust when this water lies at the bottom. But contaminated fuel is not our only source of concern. Water contamination also comes from a combination of condensation from temperature fluctuations and the hygroscopic (water-attracting) nature of modern petrol blended with ethanol (typically E5 or E10 in the UK, containing up to 10% ethanol).

Condensation
The empty space (headspace) above the fuel level in the tank is filled with air, which always contains some dissolved moisture (humidity). As temperatures drop overnight or during storage, the air cools and its relative humidity rises. When the temperature differential between the air and metal reaches a certain level, condensation forms on the cooler metal surfaces inside the tank, much like condensation on a cold window.

063 Condensation on a window.jpg (85.23 KiB) Viewed 407 times

This condensation runs down and mixes with the fuel or passes through it, eventually settling at the bottom as a layer of water.

Water alone can cause rust on the bare steel inside the tank base over time:

Simple oxidation: iron + water + oxygen → rust.

We have always lived with this problem, but the addition of ethanol in E5 & E10 petrol has changed things.

Water absorption
Ethanol is hygroscopic (it attracts and absorbs water from the air) and acts as a solvent that helps blend a certain amount of water into the petrol making it slightly cloudy.
Under normal conditions, E10 can hold about 0.5% water by volume in solution at around 15–21°C roughly 4 teaspoons per gallon.

However, its water holding capacity decreases as temperature drops: at lower winter temperatures you might be pumping fuel from a relativley warm underground tank in the forecourt and putting into your cold fuel tank (or a tank that will become very cold overnight). At lower temperatures, the fuel can reach water saturation point.

When the fuel exceeds this saturation point the excess water can no longer stay dissolved (in the way that fog forms in damp cold air). At this threshold, the ethanol preferentially bonds with the water molecules, pulling it out of solution.

Phase separation
This creates two (or sometimes three) distinct layers in the tank:
A top layer of mostly petrol, a heavier bottom layer of ethanol + water (a milky, vinegar-like mixture, sometimes called the "ethanol/water cocktail") and possibly a small acidic water layer at the very bottom as separation progresses.
This process is called phase separation because the fuel "phases" (separates) into immiscible layers.
It is temperature-dependent: colder conditions accelerate it by reducing water solubility, and warmer temperatures can delay it, but also allows more total water uptake making the fuel more sensitive to the problem.

064 E10 Dry and saturated with water.jpg (50.62 KiB) Viewed 407 times

This is a new problem we are facing because of ethanol, but its not the only one.

Oxidisation
When ethanol is exposed to oxygen in the headspace air (especially during storage or when the fuel tank isn't kept brimmed), it undergoes oxidation. This process forms acetic acid (ethanoic acid, CH₃COOH, the same acid in vinegar) and water.

The reaction is: Ethanol (C₂H₅OH) + oxygen → acetic acid + water

The acetic acid dissolves in the condensed/phase separated/oxidized water, creating a dilute acidic solution (vinegar-like) that's heavier than petrol and sinks to the tank bottom.

It is this acidic nature that poses the greatest corrosion problem.
This vinegar like liquid sits against the bare metal at the bottom of the tank, accelerating corrosion significantly more than plain water ever would. Acetic acid is particularly aggressive on mild steel (especially on welds), leading to pitting, rust flakes, and eventual tank perforation if left unchecked.

This isn't just theoretical, studies and real-world reports confirm that ethanol blends promote corrosion in steel tanks and fuel systems, predominantly via acetic acid formation.

065 Gummy Carbs.jpg (74.23 KiB) Viewed 407 times

Bugs too
Microbial involvement can worsen the problem: certain bacteria (like Acetobacter) thrive at the water-ethanol interface, they live in the water at the bottom of the tank whilst feeding on ethanol and they excrete more acetic acid (creating a process called microbiologically influenced corrosion or MIC). This is more common in long-stored fuel or underground station tanks but can occur in vehicle tanks too if conditions are right. This is a familiar problem for diesel, but the bugs thrive on ethanol too.

066 Mould.jpg (53.2 KiB) Viewed 407 times

These issue extends beyond your tank:
At petrol stations: Ethanol in underground tanks can oxidise similarly, and you might pump in already-contaminated fuel with water and acid traces. With phase transition, the water is dissolved in the fuel rather than being a contaminant (which should be removed by the separators in the petrol pump).

In carburetors: During storage, fuel evaporates slowly in the float bowls, leaving behind a concentrated fuel residue of additives, ethanol, water, and oxidation by-products. The ethanol oxidises further, forming acetic acid and gummy varnish (sticky residue from degraded petrol components). This goo clogs jets, sticks floats, and corrodes brass fittings (ethanol/acetic acid attacks brass/zinc alloys over time).

In extreme cases, a small volume of fuel (e.g., 20 ml in a float bowl) can concentrate into a thick, acidic sludge after months of sitting.

Practical Prevention Tips
How do we know this is a real problem? Because manufacturers of modern bikes have gone to the expense of redesigning their products: they use plastic fuel tanks, EFI and fuel systems that are tolerant to ethanol, water and acid.
New bike suffer less.

For those with classic bikes it seems we have entered a new age where we now have a problem forced upon us. We have to do something for bikes that are only used occasionally (especially in winter).

• If you use your bike only occasionally, use alkylate fuels like Aspen or CFS Storage Plus. These fuels are ethanol-free, clean-burning, do not degrade for up to 5 years, and prevent carburetor damage, ensuring easy starting after storage. Our problems with shared by garden machinery so these fuel are often available from you Garden Equipment center.

• Use a quality ethanol-compatible fuel stabiliser (e.g., ones with corrosion inhibitors and biocides) every time you fill up, especially if the bike might sit for weeks/months. Fuel additives can provide ethanol-specific protectors and help bind water, prevent oxidation, and kill microbes.

• Consider prioritising ethanol-free petrol where available (Tesco Momentum is E5 but tests show it often has little ethanol).
Youtube: Testing The Octane And Ethanol Content Of Tesco Momentum 99 Super Unleaded Petrol 2025 Update E5 https://youtu.be/cdHZsgiuXVQ

• Keep your tank as full as possible during storage to minimise headspace and condensation.

• Drain the fuel system (not the tank) or run it dry.

• Regularly inspect the tank interior—I picked up a cheap Chinese borescope that plugs into my phone. It lets me look inside the tank (and cylinders) whenever I want, spotting water, rust, varnish, or sludge early without disassembly.

Garden power tools (chainsaws, strimmers, mowers) have faced exactly the same issue, and the response has been practical: people have adopted ethanol-free fuels where available, used dedicated stabilisers and biocides, and integrated fuel treatment into seasonal routines. Garden machinery dealers stock the right additives and alternative fuels without fuss.

In the motorcycle community—especially among owners of classics, customs, and injected retro bikes—there’s sometimes more resistance to these extra habits, as if ethanol problems won’t affect us. Yet the chemistry doesn’t care about nostalgia or build quality. Ignoring it just leads to bigger jobs and extra costs later.

The alternative? Fit a fuel filter and hope it catches the rust flakes. Put a drip tray under the bike and wait for the tank to rust through. Sniff the garage air and pray you never smell that tell-tale petrol odour indicating a leak. And if that day comes—don’t flick a light switch or create a stray spark in a vapour-filled shed. Enough fuel vapour in the air can lead to a very rapid, unplanned disassembly of your workspace.

It’s not the end of the world—getting on top of this issue is just a simple new habit. Treat the fuel properly, check your tank occasionally with the borescope, and your bike should stay trouble-free for decades more; a bit of preventive care is a small price to keep those adventures coming.

[moizeau]

Nice build and a very informative piece on ethanol.
I have 5 mowers plus chainsaw, hedgecutter, 2 strimmers, 2 bikes on the road and a genny. Taking a carb off a mower takes 15 mins, diaphagm carbs are more complicated with the membranes and microscopic orifices. Bike carbs, as we all know are a pain, especially if you have the original airbox. That's why I've been using Bardahl Stabiliser for years. Touch wood, no problems. I gave the genny a service a while back, it sits with whatever fuel is left in it for upto a year. The carb was clean.

[DeadZedDave]

Good informative write up regarding Ethanol fuel problems. It would be good to put this piece in Bike Help and pin it to the top of the list ? Ethanol petrol is not going away and will continue to be a problem for the uninformed classic owner !
Nice Zed too by the way ! I missed it first time around but will read with interest any updates. A lot of owners are going for / only interested in creating / recreating rivet counter style original spec bikes these days and its good to see a modified Zed here.
As for any questions; what camshafts do you run and what C.R. ? Also, that looks like an early type /pre 1980 cylinder block ??
I'll watch out for updates !

[j.wilson]

Thanks guys for your replies, I will keep them coming.
Engine mods soon enough.

Next I will explore the frame mods I had to make.

Roll on the sunshine

[j.wilson]

.
Back to the W1400
My first serious work went into the Kz650 frame. I modified it to accept the bigger Gpz1100 engine and incorporate the rear end from the reinvented Triumph Bonneville; the seat, rear mudguard, grab rail, passenger rail, sissy bar, and some luggage options. Those elements would blend in beautifully and give the bike a purposeful, cohesive look reminiscent of the classic W aesthetic.

Fitting the 1100 engine into the 650 frame required some careful surgery. The sump on the bigger motor only just drops between the lower frame tubes, the clearance is tight, so every mount had to be adjusted precisely to keep the sump centred and everything aligned.
The motor fits in one place only (you can drop it a little if you are prepared to do the extra work).

For the later-spec 1100 engines, most of the original 650 engine mounts had to come off, except the top front nearside one, which I kept. I then fabricated new plates for the front offside and rear mounts, plus a tube-and-bracket assembly for the lower front mount. That lower mount gets welded in place with the engine cases temporarily bolted up using the other mounts so everything lines up perfectly.

Bonneville rear end.
To make the re-styling process far more straightforward, I took a bold but practical step with the rear of the Kz650 frame. I cut away the original frame tubes and subframe structure at the back, essentially removing the tail section entirely, I bent and welded on replacement pieces that mirrored the rear geometry and mounting points of a modern Triumph Bonneville.

The reasoning was simple.
The W650 was always designed as a respectful homage to the classic 1960s Triumph Bonneville, with very similar proportions and aesthetics from the start. That stylistic kinship meant Bonneville accessories would bolt up almost perfectly and would be in perfect proportion once the rear frame matched.
And crucially, parts for the newer Bonneville’s are far more plentiful, affordable, and readily available than trying to hunt down rare or discontinued W650-specific bits.

By grafting on this Bonneville-style rear subframe, everything fell into place effortlessly: the seat, rear mudguard, grab rail, passenger rail, sissy bar, and even luggage options all fitted with minimal fuss or custom fabrication. No endless bracketry, no awkward adapters, no compromises on fit or finish. It kept the build harmonious and practical, exactly as I'd promised myself from the beginning.

The frame could now carry the clean, purposeful Bonneville tail while retaining the Kz650 up front that could accommodate the 1100 motor.
It would look right, and work right; it made the whole re-style feel like a natural evolution rather than a forced mash-up.

Throughout the W1400 build, from the original construction in 2009–2010 right through to this midlife refresh, I made a conscious effort to use isolation dampers (rubber mounts) wherever it made practical sense.
The goal was twofold: protect sensitive components from the constant engine and road vibrations, and eliminate the harsh, fatiguing buzz that plagued so many of my earlier specials.

Rubber mounts act as effective vibration isolators by absorbing and dissipating energy before it transfers to the attached parts. They decouple the vibrating source (like the engine or road inputs) from the rest of the bike, reducing transmitted amplitude and preventing fatigue, loosening of fasteners, cracking of brackets, or premature wear on electrical connections and delicate items.

068 rubber mounts.jpg (115.3 KiB) Viewed 276 times

I applied them extensively:
• The rear mudguard is isolated it from frame and swingarm vibrations, preventing cracks or loosening over rough roads.
• The battery box is isolated to prevent cracking to the aluminium housing.
• The fuel pump on one side and electrical plate on the other are mounted with rubber to reduce noise and prevent cavitation or electrical faults from constant shaking.
• Ignition coils are bracketed with rubber mounts to protect the windings and connectors from fatigue, vibration is a common killer for coils, brackets and electrical connections.
• Horns and front indicators are isolated to stop them buzzing themselves loose or developing micro-cracks in the housings.
• The oil cooler is also rubber mounted, again mainly to protect the bracket from cracking.
• The exhaust end can uses a rubber grommet mount, this stops the mounting from cracking and the retaining bolt from coming undone. The end can is a surprisingly pernicious source of vibration.
• The headlight, instruments (Motogadget Chrono Classic), and handlebars all use rubber mounts (Suzuki Bandit 1200 bar mounts), plus additional isolation for the eyebrow headlight bracket and gauge pod. This minimises the stress on the electrics. Rubber mounted bars removes any harsh tingling through the grips, especially with wider bars.

The difference is noticeable: earlier bikes I built felt "alive" in the wrong way, constant buzz through the bars, mirrors shaking loose, electrics failing prematurely, and a general sense of harshness that wore on you after a few hours. By contrast, the W1400 rides smoother and more refined than you'd expect from a big-bore custom with this much grunt.
The rubber isolation doesn't compromise handling or feedback; it just filters out the unnecessary harshness, making long days in the saddle (across England, Wales, Ireland, or an epic run to Spain) far more enjoyable and less tiring.

It's a small detail that pays big dividends in comfort, longevity, and overall refinement, protecting parts while taming the inevitable vibes from an old inline-four (with no balance shaft) in a compact chassis. In the refresh, I'm checking all these rubber mounts for age-related cracking or compression set; most are holding up well after 15 years, but fresh ones where needed will keep the bike feeling civilised for the next decade.

Perhaps some time in the future, I’ll add a bracing kit to the frame—not that I feel the need for it right now, but it would look great and add a touch of attention to functional detail. Triangle braces down near the swingarm pivot, some tubular braces running between the top main tube and the side cradle tubes, and finally a cross-tube below the airbox that I could use to brace the rear engine mount (since the engine bolt is subject to a powerful bending moment under hard acceleration).

The biggest upgrade I’d like to make to the frame is the removal of those horrible rear foot-rest hangers. They’re clumsy, dated-looking, sheet steel pressings that clash with the rest of the bike. I’d like to replace them with a bolted-on frame section featuring elegant but simple brackets or tubular mounts welded directly to the frame.

For my current update, it’s now a matter of putting up some dust sheets in the shed and rattle-canning the frame to cheer it up.

I removed the steering bearings and all the fittings from the frame, masked off the suspension studs, and took the opportunity to Dremel away every bit of weld splatter I could find. I even cleaned out the excess paint that had pooled in the frame VIN number stamp so it would be legible again.

Once cleaned, I used Scotch-Brite pads to key the old powder coating, followed by a thorough final de-grease. Then I sprayed the frame with a couple of cans of Hycote satin black aerosol.

It has come out pretty good—not as perfect as it would have been if I’d had it blasted first to strip the old powder coat and fettled every little mark, but all things considered, I’m happy with the result for now.

To keep momentum up, I have taken the engine cases to the painter. I also picked up 65 parts that have been painted and are ready for reassembly.

For engine and component painting, I use Ted at TedsShed Motorcycle Restoration Services in Hedge End, Southampton. Ted is a specialist in vapour, aqua, wet and dry blasting, ultrasonic cleaning, welding, and fuel tank restoration. Ted does a great job, is careful and meticulous, works out issues without fuss, and has a huge ultrasonic cleaner they can drop engine cases into to remove any debris after blasting. For added benefit, their engine paint looks great and doesn’t fall off.

I can now keep things moving along by rebuilding some of the sub-assemblies while the motor is being prepped. The frame looks fresh and purposeful again in satin black, ready to carry the refreshed engine and components back into action for the next decade of adventures.

Before my md-life update can progress by adding parts to the frame- I have to fit the engine.

That means I have to get that 1400 motor modified and rebuilt.

[j.wilson]

.
What is required for that big motor.

The engine modifications were the beating heart of the W1400 project: a deliberate selection of high-quality, purpose-chosen ingredients that turned a late-model Gpz1100 A3 air-cooled inline-four into a reliable, deep-torquey 1,394cc unit perfectly suited to the light, nimble Kz650 chassis.

This section covers the components you will need to make a motor for “the serious performance enthusiast”.
The donor engine itself was chosen with care. The later Gpz1100 A3 offered the most compact physical size among the big Kawasaki fours, delivered the highest factory power output of its family, featured the largest inlet valves for superior breathing, incorporated undercut gear dogs to prevent jumping out of gear under load, and included a factory temperature sensor location in the cylinder head—ideal for clean EFI integration.

The temperature sensor is fitted to an adapter, this has the same M10 x 1.0mm thread on both the male and female side. This adapter is not there to match threads, it is there to provide a temperature gradient between the cylinder head and the sensor itself (don’t leave it off).

To reach 1,394cc from the standard 1,089cc (72.5mm bore), the key ingredient was an 82mm bore. The stock cylinder block and liners could not safely accommodate that increase, so the foundation became a heavy-duty big-block cylinder block complete with oversized liners, bored and honed to exact specification.
This complete big-block conversion was available as the APE Hot Rod Street Kit (listed in their brochure as 1395cc, though precise mathematics puts it at a smidge over 1394cc).

The pistons were Arias 82 mm forged units matched to the big-block liners, using the later-style 18mm wrist pins for added strength and reduced flex. Matching piston rings completed the top end, and the combination was set up to achieve a 10.5:1 compression ratio.
Suitable larger base and head gaskets were required to suit the revised dimensions and maintain proper sealing under higher stresses.
The crankshaft was rebuilt with welded crank pins to prevent twisting under the amplified torque loads—a known weak point on these air-cooled fours when pushed hard.

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For the cylinder head, the ingredients included high-lift camshafts (APE K435 billet type, 0.435” lift) fitted with adjustable cam sprockets to precisely optimise valve timing and allow the engine to draw more air, especially in the midrange where the lazy, arm-stretching torque lives.

Heavy-duty valve springs were fitted to control the valves reliably at the increased lift and revs (though these require replacement every ~10,000 miles in road use, as high-lift cams place significant stress on them and fatigue will lead to breakage). The later Gpz head already featured a shim-under-bucket arrangement—more reliable than earlier shim-over-bucket designs.

The intake and exhaust ports were gas-flowed to optimise airflow for the increased displacement, smoothing transitions and removing restrictions so the bigger bores could fill efficiently.

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Along with other head machining, the top needs to be machined to give clearance for the higher cam lobes.

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Four additional spark plug holes were machined into the head to create a true 8-plug configuration (two plugs per cylinder). This dual-plug setup promotes faster, more complete combustion, reduces detonation risk, and allows the motor to run noticeably cooler—particularly valuable with the higher compression and larger capacity.

A manual cam-chain adjuster replaced the automatic unit to eliminate any possibility of it backing off over time—essential for maintaining precise valve timing on a high-performance build.

The entire top end was clamped together with a full set of heavy-duty cylinder studs and nuts to handle the increased clamping forces and prevent head lift under load.

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The clutch internals were upgraded to cope with the extra torque: new clutch damper springs to eliminate the characteristic rattle that develops with age and wear, and stronger plate compression springs to ensure reliable engagement and prevent slip under hard acceleration or two-up riding.

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Don’t forget sealing the cases.
A complete new gasket set sealed everything.

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All of these carefully selected components—big-block kit, Arias pistons, APE high-lift cams and adjustable sprockets, heavy-duty valve springs and studs, manual cam-chain adjuster, gas-flowed and 8-plug head, rebuilt and welded crankshaft, upgraded clutch—were assembled meticulously by Ray and Steve at Debben Performance in Ringwood. The basic outline here does not capture the hours of measuring, inspection, and setup required: piston-to-head clearance and compression ratio, piston-to-valve clearance at full lift, repeated assembly/disassembly cycles to get everything perfect.

The original engine was built in 2011 and the bike has covered 20,000 miles since. After 15 years of riding, the refresh revealed:
• Worn piston rings
• Broken valve springs (clear confirmation they need replacing around 10,000 miles)
• Loose output shaft bearing and worn spline (new shaft fitted)
• Badly worn titanium valve retainers with chunks missing (replaced with standard retainers)
• Damaged valve guide oil seals (from broken springs—replaced with new)
• Broken clutch transmission springs (replaced with new)

A new gearbox output shaft was required because of its lifetime of wear. It is great that this is still available from Kawasaki.

The result is an engine that delivers deep, effortless midrange torque without sacrificing reliability or refinement—perfectly complementing the W-series styling and Kz650 handling. It starts eagerly, pulls cleanly from low revs, and feels like it has genuine muscle under the classic retro skin—exactly what the project set out to achieve.
With the midlife refresh now underway, the engine is being stripped for inspection and refresh. The big-bore kit, flowed head, and welded crank have held up impressively after 15 years and high mileage, but fresh seals, gaskets, bearings, and replacement of wear items will keep it in top form for the next decade of adventures.

[j.wilson]

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Upgraded Starter Motor
Starting the bigger mill reliably was another consideration. The standard Gpz1100 starter motor (0.6 kW) struggled to spin the increased compression and displacement—often cranking sluggishly or drawing excessive current. The chosen upgrade was a higher-output 0.8kW Mitsuba unit (model 438 or SM220), the same one used on the Hodna CB1100R from 1980–1983. This beefier starter turns the engine over emphatically, even on cold mornings, without taxing the battery or electrical system unduly. Fitment required only minor adaptations to the transmission case to clear the new electrical connection position and a little machining on the starter motor case.

Hydraulic Clutch Conversion
For smoother, lighter operation, the clutch was converted to hydraulic actuation. The slave cylinder came from a Kawasaki GT1100 (a later shaft-drive tourer with similar engine architecture), and discreet mounting hardware was fabricated to tuck it neatly behind the transmission case—keeping the left-side lines clean and out of harm’s way. This setup provides a more progressive lever feel than the cable original, with less maintenance and better modulation for traffic or quick shifts.

[j.wilson]

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Crank sensor

The ignition triggering got a modern twist too. I was cautious with rotor pickup housings—there are several points covers are available, but they vary significantly in design, and earlier ones don't position the oil seal correctly, leading to leaks and contamination over time. To get the setup right, I used a previous engine pickup casting (from a Gpz) specifically because it allowed me to mount a different style of crankshaft sensor more easily.

I also used a new timing wheel (thanks Lee) — a toothed rotor with one tooth deliberately missing to provide the ECU with a clear reference point for cylinder #1 top dead centre and overall timing synchronization. This custom trigger wheel ensures precise, repeatable signals without relying on worn or mismatched stock components.

The sensor I chose—a 25mm long Cherry Hall Effect unit—wouldn't fit neatly inside the standard pickup casing due to its length and orientation. Rather than force a compromise, I carefully machined a hole through the casing to pass the sensor body and its wiring, then sealed everything with a neatly domed cap over the opening. This kept the assembly weatherproof, protected the wires, and maintained a tidy appearance while allowing the Hall Effect sensor to sit at the optimal air gap to the trigger wheel.

As a reminder: be extremely careful when selecting or modifying any pickup casing. Beyond the obvious fitment issues, the position and style of the oil seal differ between variants—get it wrong, and you'll end up with oil weeping past the seal, contaminating the sensor area.

Hall Effect sensors offer clear advantages over traditional variable reluctance (VR) pickups. VR types induce a signal in a coil as the magnetic field is interrupted by the teeth on the gear wheel, but they're notoriously gap-sensitive and speed-sensitive—the amplitude of the signal varies with engine cranking speed (weaker at low RPM, potentially causing starting issues) and requires precise air-gap setup to avoid weak or erratic readings. A Hall Effect sensor, by contrast, requires a small power supply but delivers a clean, well-defined square wave output through its internal circuit and encoder—consistent at all engine speeds and tolerant of minor air-gap variations, making it far more reliable for ECU triggering.

To prevent electrical noise, I ran the sensor cable in shielded wiring, grounding the shield properly to avoid picking up stray interference from the ignition coils (which can act like an antenna and introduce false triggers or timing jitter).

This combination—custom timing wheel, carefully chosen and modified pickup case, domed cap for sensor accommodation, and shielded Hall Effect setup—gives the ECU rock-solid, noise-free input for precise ignition timing across the rev range. No misfires, no drift, and smooth response whether cold-starting or ripping through gears. It was one of those detail-oriented steps that ties the whole EFI system together without drama.
With these engine mods—big bore kit, flowed head, high-lift cams, 8-plug conversion, rebuilt crank, hydraulic clutch, upgraded starter, and now this refined ignition triggering—the GPZ1100 heart feels reborn: torquey from idle, responsive at any revs, and reliable enough for daily adventures. The W1400's powerplant is no longer the weak link—it's the star, delivering exactly the effortless, character-filled shove I set out to achieve.

With the engine ingredients and key supporting upgrades outlined, the photographic record of the assembly and refresh will follow in due course.

For now, the focus shifts to the other parts of the build—frame refresh, sub-assemblies, paint, and reassembly—while Ted at Ted’s Shed works his magic on the cases and components.