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

[sockpuppet]

Hi

Thanks for confirming those details , i like the more your more discreet conversion rather than the more usual outrigger plate solution .

I have been experimenting with a slave cylinder and spare outer case that i`ve butchered inside to mount it,

but i like your idea better so i think i`ll have a go at that instead .

cheers
Mick

[chrisNI]

Good stuff keep it coming

[DeadZedDave]

[j.wilson]

To get a decent feel to the lever and the right amount of travel, you have to match the lever cylinder and the slave cylinder.
I looked at loads of more compact clutch slave cylinders, but they were too small and force you to find small master cylinders.

In the end, the GT1000 slave with the 34mm bore was a decent choice; it allows for a 12-14mm master cylinder bore.
This has 3 mounting points and needs to be orientated for the hydraulic cable exit and to put the bleed hole to the top.

The mounting points for the transmission cover (looks like I've been calling the outside "front chain cover" the wrong name)
don't lend themselves to mounting the slave cylinder, because no two of them line up with the center of the clutch pushrod.
You get a bending moment.

To use three of the existing screws on the transmission cover to share the load, would mean reaching far over the other side
of the cover - making the bracket really big.

My solution was to make a cantilever support. The plate that holds the slave cylinder has two mounts that are in line with the
clutch pushrod, one 33mm away, the other, over 70mm the other side. A third mount was added just to prevent twist.
There was little penalty to adding the third - especially as I was using the screw below.

I used a simple lower cantilever bar that spanned two transmission mount screws and allowed me to extend the upper plate
support screw so its lined up perfectly.

Because the cantilever section of the lower bar is nice and close to the mounting screws, I'm not worried about it bending.

The only other detail I added, was to provide a retainer that prevents the spring loaded piston from popping out when the
assembly is removed from the bike. This might be necessary when the chain is changed.

I hope this all makes sense. With the parts away for painting I'm a little restricted in the pictures I can provide.

[j.wilson]

Thanks for the encouragement, feedback and questions guys, it motivates me to keep it all coming.
When I don't get any responses or questions, I feel that perhaps its wasting everyone's time.
I'm no way an expert, so feel free to point out where I'm adrift.

[j.wilson]

.
The chassis:
The rolling chassis presented its own set of considerations once the bigger engine was in play. The standard Kz650 swingarm is relatively short, typical of mid-1970s designs, with a wheelbase around 1,437mm and a compact rear end that keeps the bike nimble and flickable in stock form.
But with the bored-out 1394cc Gpz1100 motor now pumping out significantly more torque (easily north of the original 1100's rear wheel torque of 63ftlbs at 8000rpm) that short swingarm would make the bike far more prone to lifting the front wheel under hard acceleration and less stable at higher speeds or when loaded.

To counter that, I decided it was wise to replace the stock swingarm with a longer, stronger one—aiming for roughly 45mm of extra length from pivot to axle. That modest extension would stretch the wheelbase enough to improve straight-line stability, tame wheelie tendencies under the added grunt, and give the bike a more planted, confident feel without turning it into a stretched-out drag bike. The extra length also helps deliver the increased power more manageably, especially with the lazy midrange delivery I was after.

Careful selection of the chain tensioner design is important. The higher torque output has a real tendency to twist and pull around simple clamped-cam adjusters found on some aftermarket setups, leading to rapid, unplanned chain adjustment.
I went with a custom JMC arm made of 7020 alloy and using a well-engineered tensioner that could handle the stress without slipping or requiring constant fiddling.

This upgrade kept the build practical and safe: preserving the stable handling DNA of the Kz650 frame while making it capable of dealing with the serious muscle now living up front. No wild extensions or radical geometry changes, just enough thoughtful lengthening to let the extra power shine without drama. With the rear subframe already mirrored to Bonneville specs for easy accessory fitment, the chassis is now ready to tie everything together into something that will ride as composed as well as it looks.

Tyre choice:
The tyre choice was one of the earliest decisions I locked in, because there's simply no sense in picking exotic wheels or rims if the tyre options are limited or non-existent; availability had to dictate the direction from day one.
I chose a 19-inch front and 17-inch rear combination, a sizing that's widely used on big adventure bikes with similar overall weight and speed ranges. It gives the front wheel enough height for that classic 60s stance, while the rear tyre's higher section profile brings the overall rear wheel diameter closer to what you'd get from an 18-inch setup. That helps preserve the bike's geometry, handling balance, and visual proportions without throwing the rake or trail out of whack.
I went with radial tyres without hesitation; the improvement is immediately obvious. They sharpen up steering response, deliver far better grip (especially in the wet), offer more compliance over bumps, and bring a level of refinement that cross-ply tyres just can't match. The difference feels modern and planted, yet it doesn't clash with the retro character I'm aiming for.

On the rear, I kept the width to no more than 150mm to stay well within practical limits; no need for an outrigger bearing on the transmission output or major clearance headaches. A wider tyre would have complicated the chain run and swingarm geometry unnecessarily. My lateral engine location is pretty fixed because of the limited modifications I made to the frame; the sump only just fits between the lower cradle tubes. That dictates how far off-centre the engine sprocket is and therefore how wide the back tyre can be.

With the tyre sizes chosen, that opened up plenty of excellent, readily available radial adventure-touring options in sizes like 110/80-19 or 120/70-19 up front, and 150/70-17 (or equivalent 140/80-17) at the back.

After testing a few combinations for feel, grip, longevity, looks and compatibility with the bike, I settled on the Metzeler Tourance range, proven all-rounders, with excellent road manners, strong wet performance, and good mileage.

The rear is a Metzeler Tourance 150/70 R17 M/C 69V, which fills the rim perfectly, provides a tall sidewall for that classic look and compliance over potholes, and offers confident traction under the extra torque without feeling twitchy.
Up front, I fitted the matching Metzeler Tourance 110/80 R19 M/C 59V, tall and narrow enough to keep the ride smooth s with a progressive profile that works beautifully with the longer TRX850 forks and the bike's upright geometry.

These Tourance tyres suit the W1400's intended role perfectly: they have a chunky look yet roll smoothly and noiselessly on motorways, grip hard on damp lanes, wear evenly on long-distance rides, and maintain that period-correct stance without looking overly modern or aggressive. They're widely stocked, easy to source replacements for, and have a reputation for predictable handling and confidence-inspiring feedback, exactly what the project needed to deliver the extra engine torque and braking power.

Wheels to suit
To keep the authentic retro look and add rim options, I opted to keep the spoked wheels and 40-spoke rims. For the front, I chose a Morad alloy rim measuring 2½ x 19 inches, wide enough to support the 110/80 R19 Metzeler Tourance tyre properly.

The Morad rims are known for their high-quality extruded aluminium construction, excellent strength-to-weight ratio, and precise machining, which makes lacing them up straightforward and ensures they stay true under hard use.

At the rear, I fitted a matching Morad alloy rim sized 3½ x 17 inches. This width properly forms the 150/70 R17 Metzeler Tourance profile, providing good sidewall support for the taller profile while maintaining clearance for the chain and swingarm. The 3½-inch width strikes a good balance: wide enough for a good contact patch that provides grip and stability under the extra torque, yet not so broad that it requires outrigger bearings on the gearbox or forces major chain line compromises.

Both Morad rims are dimpled for the spoke nipples, which helps with even tension and long-term trueness, and their black powder coated finish adds a subtle elegance without being overly flashy.

Lacing them to the retained original Kz650 front and rear hubs was uncomplicated- the hubs' spoke flanges aligned well with the new rims, and I used stainless steel spokes for corrosion resistance and durability.

The combination—Morad 2½ x 19 front and 3½ x 17 rear—delivers classic proportions that suit the bike's retro muscle stance, while the alloy construction keeps un-sprung weight reasonable and improves responsiveness compared to heavier steel rims. With the Metzeler Tourance tyres mounted, the setup rolls smoothly, grips predictably in wet or dry conditions, and maintains a tall, soft profile that works so well with the longer forks and stretched swingarm.

I retained the original Kz650 front and rear hubs, they're among the few stock parts I kept because they bolt up cleanly, maintain bearing compatibility and have the integrated cush drive; this helps keep unnecessary costs down.

The wider rear tyre and chain alignment did require custom wheel spacers to centre everything properly with the engine sprocket. I fitted a 5/8” offset engine sprocket carrying 17 teeth on a 530 chain; this provides the swingarm with enough clearance for a clean chain path, while avoiding contact with the wider tyre sidewall and the lower ends of the shocks.

In the end, it all came together sensibly: the tall radial Metzeler Tourance tyres for contemporary ride quality and grip, proven sizing for easy availability and balanced performance, premium Morad alloy rims for classic style, strength, and light weight.

The bike now rolls with confidence under the extra power, looks period-appropriate and well proportioned from every angle, and runs on rubber and rims that are practical to maintain for the long haul.

Front suspension
The front end required a thoughtful upgrade, as the stock Kz650 forks, classic mid-1970s damper-rod design, felt under-gunned for the bike's new weight distribution, braking power, and the kind of real-road riding I had in mind. They lacked rigidity and sophisticated damping needed to cope without becoming overwhelmed- not to mention they were pretty worn out.

The Kz650's steering head sits relatively high, so replacement forks need sufficient length to preserve proper rake, trail, and overall geometry. Dropping the front too low would make steering unpredictable and compromise stability.

I chose Yamaha TRX850 forks (41 mm stanchions) as the upgrade path.

These forks offer a clear step up in strength and build quality from the 1990s era, delivering noticeably better rigidity and a more modern, compliant feel. Ideally, I would have used the original Yamaha yokes, but the top triple clamp does not drop far enough to compensate for their length.

Instead, I designed a complete new set of yokes (triple clamps) and stem (thanks to Lee for making the steering stem) and had them machined to connect the TRX forks to the KZ650 steering head. The top yoke steps down significantly to position the forks at the correct height, while spacing the larger-diameter stanchions wide enough for the front mudguard to fit neatly between them, the brake calipers to clear the wheel spokes, and the whole assembly to turn lock-to-lock without fouling the fuel tank. The design also incorporates rubber mounts for the handlebars and instruments, plus a dedicated mount for the sat-nav unit.

I put considerable effort into styling the yokes to look like factory cast items—reminiscent of the original KZ650 triple clamps—so they blend seamlessly rather than scream “special”.

I initially hoped to 3D-print the yokes in metal, but the cost proved prohibitively high, so I abandoned that route. I did have two prototype sets 3D-printed in plastic purely to prove the design and check fitment before committing to metal. In the end I used a much more cost-effective layered CNC machining technique: you supply the engineer with a CAD file, the model is sliced into very thin layers, and a small tool follows the contour paths layer by layer, carving out the complex curves.
The machining was carried out by M&K Enterprises Development Engineers at Elmwood Farm, Rouncil Lane, CV35 7AL (tel: 01926 245000).

126 3d machined part.jpg (124.65 KiB) Viewed 225 times

With the yokes painted, I carried out a full test assembly of the yokes with all the related components to confirm everything fitted and functioned as expected. There is a great deal going on in that area—and the yokes turned out to be the second most expensive single component on the entire bike.

The finished front end now looks far more integrated and “designed”. On the road it feels planted and confidence-inspiring: smoother over imperfections, better feedback under braking and in corners, and perfectly matched to the bike’s geometry and muscular character. It’s a significant upgrade that makes the W1400 handle like a much more modern machine while still looking neat and period-correct.

[j.wilson]

Mick, if its helpful, here is the dimensions of my clutch slave cylinder mount.
Sorry for the scrappy drawing.

[sockpuppet]

Many thanks for that !

That will be very useful ---- saves me having to spend many a happy hour working out all the mounting dimensions.

I only have a hacksaw , drill , files and enthusiasm at my disposal so it probably won`t be as elegant looking but should be able to make something functional.

thanks again

Mick