8. Milling, Fitting, and Finishing Touches

LEFT SIDE AXLE SPACER:
The left side is easy.

You mill 2.5mm from the inner side of this spacer.

You take the left side wheel spacer and mill down the inside
surface by the required 2.5mm.
My neighbour has several metalwork lathes and was willing
to do the work for me.
I am fortunate, as he builds his own race cars, and modifies
and fabricates any parts he needs.
He is old school, so calculates each machining into thou.
(thousandths of an inch)
So when I say we took 2.5mm off the left side spacer,
I mean we milled exactly 2.5mm off.
He translated the required reduction into thou,
then milled down the spacer.

ADVICE:
If you are going to follow this rear wheel conversion procedure,
I guess this is the part where I have provided some measurements
as I did them, and you should still do your own measurements,
but you have to decide if you are going to get a metal work expert
to do the actual machining.
Because once you take metal off, you cant put it back on again.
If you screw it up, you will have to source new spacers or
fabricate them from scratch.

RIGHT SIDE AXLE SPACER:
The right side is a bit different.

There are effectively two spacers.
The inner most spacer next to the wheel, and the brake caliper
mounting bracket.

See the two spacers. Inner Spacer (left) and Outer Sleeve-spacer (right).

The inner spacer should not be touched.
It is recessed, again, onto the wheel bearing.
There is not enough to work with here, to mill the required
4.5mm off, and still have the spacer protrude from the wheel
bearing rubber seal. So leave it alone.

BRAKE BRACKET SPACER:
The option here is to modify the brake bracket spacer.
The brake bracket has a 'hard' metal spacer that runs through
the softer alloy of the actual brake caliper mounting bracket.
Let's call this the 'sleeve-spacer'.
The unmodified brake bracket sleeve-spacer sits almost flush,
on the inner side of the brake bracket.
But protrudes on the outer side of the brake bracket, against
the R# swingarm-swivel axle mount.

NB: The ZZR600 brake bracket has NO sleeve-spacer.
It is only a 'soft' metal axle spacer itself.

The sleeve-spacer needs to rest against the right side
(outer side) of the inner spacer.
 - Hard-metal against hard-metal.

And also the protruding (flanged) side of the sleeve-spacer
needs to rest against the R# swingarm-swivel axle mount.
 - Hard-metal against hard-metal.

The brake bracket must be able to rotate freely when the
wheel assembly is installed and tightened.

I decided to get the required 4.5mm (in thou) milled off the
inner side of the sleeve-spacer.

Mill 4.5mm from the inner side of the Sleeve-Spacer, and recess the Brake bracket.

Sleeve-spacer.

Sleeve-spacer inserted and just raised from brake bracket.

Sleeve-spacer inserted (inside view) and just raised from brake bracket.

Then, recess the brake caliper mounting bracket the required
amount (which is slightly less than the sleeve-spacer flange
width), so the now modified sleeve-spacer fits nicely through
the brake caliper mounting bracket, but protrudes just a few
thou each side to give the required hard-metal to hard-metal
contact on both sides.

When you have done this, the axle spacer work is complete.
And there are just a few more finishing touches.

BRAKE BRACKET SLIDE BOLT:
You can check when you bolt it all up, that all hard spacer
surfaces mate properly, and that the brake caliper mounting
bracket spins freely, as I said before.

You must now mill down the outer brake caliper bracket
surface, where the slide-bolt goes to prevent the brake
caliper bracket from spinning. This is where you fix the
caliper bracket to the R# swingarm.
I think it was about 2.5mm, but you can measure it.

The Original GPz900R brake bracket no longer fits when the sleeve-spacer is milled.

See where it hits the Swingarm slide-bolt bracket.

Only a few mm needs to be milled off this section.

You pretty much grind the 'flanged' section back to being
flush with the rest of the bracket.
Once this is done, the brake caliper bracket can spin a full
360deg around the axle, once the wheel is installed,
and everything is fully tightened.

I did this with a hand file. Didn't need to be perfect.

I think I ended up with another 1 mm off this.

Just a bit thinner ... Until it fits.

And finally you need to get yourself a 1mm washer to
replace the original 2mm washer, that fits inside the
axle nut, on the outer side of the swingarm.
Remember I said this is required to give you back 1mm
of axle thread you lost by not compressing the swingarm.

You only use the NEW thinner washer. (comparison shown)

It all should be done and ready to bolt up.

GPz900R - Rear brake bracket - installed.

ZZR1100 - Rear brake bracket - installed.

17 Inch Rear Wheel Bolted in Place. (left side view)

17 Inch Rear Wheel Bolted in Place. (right side view)

REAR BRAKE CALIPER:
Next attach the brake caliper.

Original GPz900R caliper and bracket, with a matching ZZR1100 250mm Disk.

I needed to move the brake caliper inward by about 4.5mm
to cater for the changes.
I just got some longer allen headed high-tensile bolts of the
required length.
I only had 3mm thick steel washers, but there is a generous
amount of room on the caliper slides, so these did the job well.

Can you see the 3mm washer - between the brake mount and caliper backet.

These washers go on the inside of the caliper bracket
between the caliper mount plate. 
I did shave a few mm from the back of the allen headed
mounting bolts, to give a bit more clearance to the disk
rotor surface.
They are now flush with the fully installed caliper plate.

CHAINGUARD:
One final modification is required for the chainguard
clearance to the new 17" tyre bead.

The 17" tyre now sits closer and lower to both the plastic
chainguard, and to the metal chainguard guide on the L#
swingarm.
I simply cut a recess in the plastic chainguard.

You need to make room for the Tyre.

So make a simple recess cut in the plastic Chainguard.

Pretty easy modification.

I also simply filed the chainguard guide on the swingarm
at an angle, and rounded the edges, to give me the clearance
I required.
Not a hard task.
No measurements, you can work this out for yourself.

Original unmodified Chainguard guide - dirty.

Next...

File a nice angle for Tyre clearance once installed.

Just hand done, with rounded edges.

CENTRESTAND:
You can do the centrestand yourself, if you want to have one.
I like having a centrestand on a bike.
It makes it easier to work on the bike, in the garage.
If you got yourself a Kawasaki GTR1000 unit, like I said,
then you should be able to work out the
clearances required. see my previous notes on this.
I have not modified my stand yet, but I do intend to do it.
I also got a spare ZZR1100 stand for about $25Aud.
I may consider using the top of the GPz900R stand, and the
bottom of the ZZR1100 stand, which has a nice wide base,
and weld them together to fabricate a better stand.

That's it !
Done.

You should now have a 17" wheel fitted into your GPz900R.

Does it look okay ?

Factory Fitted ?

Now go for a Ride.

Finished Bike... for now...

Now with K&N filters and the New carbs. (next the SS Exhaust !)

MY ADVICE:

Please note, I am not a mechanical engineer.
I am a reasonabley experienced home mechanic.
Not a qualified mechanic.
I do use people's advice.
I have learned people available for support.
I am not going to make any dangerous modifications.
I do not wish to die because I made a stupid, unsafe,
or uncalculated modification.
I may perfect the alignment at a later stage.
(add 2mm on the right, expand swingarm)
This procedure is a guide to what I did.
You must use it as a guide, and for information.
Get your work checked.
Do your own measurements.

Remember,
You can't beat Qualified and Experienced Professionals.

PS: I did take this to my Kawasaki shop for a look.
They thought it was a pretty good job too.

Thanks and Stay Safe.

7. Measuring Up

Next to measure spacers.

I found that there is not really much space to work with on the
left hand side.
The left side axle spacer is recessed onto the left wheel bearing.
The spacer rests on the internal swingarm swivel mount.

I needed to move the ZZR600 wheel centreline over by a total
of 3.5mm to the left.

I checked the available space on my ZZR1100 so I could leave a
reasonable space within the swingarm to the spacer/sprocket side.
You need to have some clearance but it can be minimised from
the ample space the original GPz900R wheel spacer has.

ZZR1100 has only 2.5mm space.

ZZR1100 Left side clearance is 2.5mm.

My ZZR1100 has almost 2.5mm space on the left hand side.
(hard to measure without removing the wheel, but accurate
enough for a tolerance estimate)
This relieved me as I didn't want to go that close on the
GPz900R at first, but after I measured the ZZR1100 clearance
I allowed myself to use at least the same tolerance.

Reference:
The midpoint of each wheel, as manufactured, is right at the
midpoint of the swingarm, and of the axle and spacers.
After careful measurements:-
 - the GPz900R wheel has a midpoint of 119.5mm
  (ie: half the measured 239mm total)
 - the ZZR600  wheel has a midpoint of 124.5mm
  (ie: half the measured 249mm total)

I also had to measure the outer surface of the wheel sprocket
to make sure it would correctly align with the drive sprocket.
There is a difference.
The ZZR600 sprocket is 3mm further left than my GPz900R
sprocket outer surface.
This is a difference that needs to be addressed.
It might not sound like much, but it may cause wear issues
if the misalignment is too large.
It may only be premature wearing out of the chain and
sprockets, but it may also result in a potential chain break,
as components will be stressed during uneven wear.
I may need to find an offset sprocket or shim down 1mm off
the bolted mating surfaces.
The sprockets are both 10mm thick.
The chain is a 530.
My GPz900R 'aftermarket' sprocket is a 48T.
The sprocket I have on the ZZR600 wheel is a ZZR-45.
(same as on my ZZR1100)

So, to move the centreline over to the left by the required
offset, there are several options.

If I took 3.5mm/3.5mm off each side, the wheel centreline
would be where the original GPz900R wheel was, however the
sprocket would be 3mm to the left of original sprocket,
and I would only have 1.5mm tolerance for the wheel spacer
on the left side swingarm.

Therefore based on the left side spacer tolerance I require,
and considering the sprocket alignment, I have decided to
only mill 2.5mm off the left side of the ZZR600 spacer,
and 4.5mm off the right side sleeve-spacer.
 - Remember I need to reduce the overall axle spacers by 7mm.
 - I need to keep a tolerance of 2.5mm on the left hand side.
   (same as ZZR1100)
 - I need to consider the sprocket alignment.

So, in choosing 2.5mm/4.5mm L#side/R#side, the centreline
will be 1mm right of original, and the sprocket is only 2mm
left of original, and I have the 2.5mm tolerance on the left side
swingarm.
The wheel is now centred at 122mm. (from the left)
Remember the measured swing arm 'uncompressed' is 242mm
so to be centred it needs to be 121mm.
But over the length of the chasis that is only a 1mm wheel offset.
I can live with that.
Please note that I may resolve this issue in future and perfect
the centreline with further machining or shimming.

This also means that the sprocket comes back to 2mm to the
left of original now.
That is within a satisfactory tolerance for the chain alignment,
considering the length of the chain.
No further action required here.

And this means I have a left side clearance of 2.5mm, just like I
measured on my ZZR1100.

Now to shim/mill it all, and fit it up.

Then do the brake bracket.

6. Centreline

Now the main thing you need to concern yourself with, when
measuring up for the fittment of the new 17" ZZR600 rear wheel
into the original swingarm of your GPz900R, is the centreline.

You can take it as given that this wheel does in fact fit into the
original GPz900R swing arm, even though it is 4.5" wide and
the original 18" wheel is 3.5" wide.
The tyre that was fitted to this 4.5" wide rim is a 160/60/ZR17.
Although from the finished installation it may be possible to fit
a 170/60/ZR17 onto the rim and still have enough clearance.
Also, you would need to consider the effect this would have
on the handling of the bike.
I have not done a comparison yet, however I can tell you the
160/60 rides pretty well.
And the bike tracks well, and doesn't seem to push into corners.
A 170/60 may lift the rear a little and make the bike turn in more.
It may also have a little bit wider camber, so you be the judge.

Once you establish this centreline, you will know how much to
shim and rework the axle spacers to give you the correct offset
to ensure your new wheel centreline is where the 'original'
wheel centreline was.
What I mean by wheel 'centreline' is the middle of the rim.
The midpoint of the wheel from the the left rim to the right rim.

So, with both wheels removed, the axles installed and all the
bracketry, and spacers that are internal to the swingarm,
I measured the total width of each.
The ZZR setup was a full 10mm wider from spacer to spacer
 - internal to the swingarm.
 - GPz900R axle spacer to spacer = 239mm.
 - ZZR600   axle spacer to spacer = 249mm.

So, if I am to use the original GPz900R axle, I need to reduce
the total width of the spacers and brackets by 10mm, so it all
fits into the original swingarm.

Axle and Spacers - Full Setup. (NB: only one washer used) 

Left rear axle Spacer. (gets reduced by 2.5mm)



Right rear axle internal Spacer, and Brake bracket Sleeve-Spacer.

I measured the 'uncompressed' swingarm - from internal (R#)
to internal (L#) and found I could save about 3mm from when
the swingarm is compressed with the original GPz900R wheel
installed and everything tightened.
 - Uncompressed internal swingarm = 242mm.

Uncompressed GPz900R Swingarm.

So, now I only had to lose 7mm from the total ZZR600 axle
spacers, and get the wheel centred.

I did not want to expand the swingarm to gain anymore space,
as doing this would mean I would lose available threads from
the axle. And I have already lost 3mm based on not compressing
the swingarm.
Also I did not want to stress the swingarm welds by expanding.
However based on the fact that it does compress the swingarm
by 3mm, there may be some flexiblity there to expand slightly.

To regain 1mm extra axle thread, I used a thinner washer for
the axle nut, external to the swingarm.
There are plenty of threads being used for tightening the axle
nut, so no issues here.

Right Side Axle Nut - with NEW 'thinner' washer, and OLD 'original' washer.

When I measured the offset, I found the centreline of the
ZZR600 wheel to be actually 5mm offset to the right of the
original GPz900R wheel.
This means that Kawasaki has the centreline of each wheel
at the exact centre point of of each axle including the spacers.
The wheel centreline is exactly in the middle of the swingarm.
Good to know.

This may not always be the case.
A wheel does not have to be centred in a swingarm.
The wheel centreline needs to be centred based on the whole
chasis with respect to the front wheel.
The rim distances may not necessarily measure the same
from both sides of the swingarm.
You must measure the axle spacers to rim, on both the left
and right side to be sure.

So, in my case, if I need to take 7mm from the spacers,
then I need to take 3.5mm from each side and retain the
correct wheel centreline.
And then mill down the spacers and brackets accordingly.

Next to measure spacers.

5. Find your Wheel

The reason for this particular blog is to illustrate my 18" to 17"
rear wheel conversion.

The GPz900R has an 18" rear, and I am finding it hard to get
decent sticky rubber.
By this I mean Z-rated.

The rear wheel size is 18" diameter and 3.5" wide.
I had a Michelin MACADAM 150/70/ZR18 fitted.
No-one had these anymore. Not instore nor on the Web.
I just could not find an 18" tyre to suit nowdays.
I even spoke directly with Yokohama, Dunlop, and Michelin.

So, even though I am happy with the 18" and the 150 size
(the original GPz900R before A7 had a 130/18 rear), I decided
to do a rear wheel conversion to a 17".
This seems to be a commonly adopted size now, and of course
means plenty of available tyre choice.

Firstly to investigate the options.

How big is enough ?
Can I do just the wheel, or do I need a swingarm too ?
How costly ? And how much do I want to spend ?
And can I do the work at home ?

So, Check out the Web.
There doesn't seem to be any information that I can find
regarding 17" rear wheel conversions specific to my GPz900R.
Comments but no details.
Has nobody done this before ?
Doesn't anybody want to share information ?
Or is this the realm of the mechanic only ?

Well, after a bit of running around and speaking to the right
people, racers and wreckers.
I decided to settle on a pretty straight forward conversion.
It might not be perfect (yet) but it will suit me.
It is simple.
And I will share.

In the years of 1990/1991/1992 the Kawasaki ZZR600 came
out with a rear wheel that is 17"(dia) x 4.5"(wide).
And also most importantly it has the exact same axle diameter,
I think 17mm (I might need to confirm this), as the GPz900R.

The later model ZZR600 has a bigger diameter axle - known
as the 'big axle' ZZR600 wheel.
You can check the year of the wheel manufacture by looking
at the embossed markings on one of the 3 spokes.
On the ZZR600 wheel, the markings are on the right hand side.
The year of manufacture is on the spoke that has the "Kawasaki"
"MADE IN JAPAN" printed on it.
You will see a circle with a split number in it.
In my case it has 9|2 in the circle. ie: 1992.

Check out the Manufacture Date of the Wheel.

The wheel is also a 3 spoke Enkei in exactly the same style,
apart from a very minor cosmetic difference with the spoke
hole shape in the hub being round instead of elongated.

So, I have sourced one.
A complete one. (axle, brake disc, cush drive,
sprocket carrier, sprocket, even a pretty good tyre)
Basically pulled out of a 'wrecking' bike.
Cost $500 Aud.
That seemed about right. But the trick is to get the whole deal.

The Old and The New.

The disc is a 230mm ZZR600 unit.
You will need to get yourself a ZZR1100 unit which is the
required 250mm, then you can use the original GPz900R
brake caliper and original mount - once modified.
 - The GPz900R 250mm disk is a 6 bolt pattern and the
   ZZR1100 250mm disk is a 4 bolt pattern.
 - Note that the A7 has a 250mm rear disk in my example.
 - The A1-A6 may be a 270mm (or 280mm) so you may need
   to fiddle with the mounting bracket to align the caliper.
I paid about $50 for a very usable ZZR1100 rear disk.

You may wish to try the lower mounted ZZR600 single piston
rear brake caliper setup for the 230mm disc, but I wanted to
keep it simple, with sort of the original look, and also use
what I already had.
If so, buy the ZZR600 brake caliper and make sure you get
the axle spacer caliper mount.

Oh, and while you are sourcing parts, get yourself a Kawasaki
GTR1000 centre stand.
It fits exactly. Using the original centre stand mounting bolt.
It is wider at the base by about the same amount you are
increasing your tyre width. I assume the GTR had a wider tyre.
You will see that it is longer too.
I can get the bike up on the centre stand, but it really should be
shortened to cater for the lower 17" tyre profile. It's hard to lift.
Maybe shorten the base of the stand by about 1.5" and reweld
the slide plates. I have not done this yet.
And I had to prevent the stand from fully raising by about 1" to
give better tolerance between the stand centre bar and the tyre.

Next thing is to measure everything up.

4. A Few More Reasons and My Mods

A few more things with regard to My A7 modifications:

I must note with regard to the rear wheel, the 18" hub on the GPz900R
seems to be well over-engineered.
Comparing it to my ZZR1100 rear hub, they both have a five spoke
cush-drive, the 900R seems to be built much thicker and stronger,
so I would assume it could take a huge increase in power.
Whereas the ZZR600 17" wheel hub is a 3 spoke cush-drive, and although
it is more than adequate for my 'street' GPz900R conversion,
I would not try and put 200bhp through it.

I also like the fact that this engine has locknut-adjustment on tappets.

It also has good switch gear and instruments, and a good screen.
I find the GPz900R more stable at 110kph than my ZZR1100.
Maybe because it is narrower.

It has good lights.
Headlight (same as GPz400, and other GPz's etc.), Blinkers, and Tail-light,
are big and quite bright.
Put in a Philips X-treme Series Halogen 55/60W H4 bulb in the Headlight
and you double your night vision capacity.
They are bright and legal.

I tried LED tail-light bulbs, the GPz has 2 bulbs, but they are not as good
as standard 6W/21W tail-light globes.
You need a bulb that 'spreads' the light within the tail-light reflector, to
light it up correctly.
The LED bulbs I chose only focussed their light rearward, so the spread
of light was actually reduced.
The LED bulbs that do spread light are VERY expensive.

I like the fact that I can touch the ground with both feet while sitting on
the GPz900R. The seat height is good for short legs.
And the 17" rear wheel has lowered the seat by nearly an inch.
Although I may spin the rear swingarm axle-mounts 180deg to lift the
rear again - for better handling. (a 1.5"- 2" raise)

The only differences when I replaced my Keihin CVK34 carburettors for
a newly (refurbished) rack of 4x Keihin CVK34 from an A6, is that the
older version had exactly the same jetting and all settings the same except
for the main jet which is *135 on the A6 model, and it is a *100 on the A7.
I think this is part of the de-tuning the A7 suffered.
Mine now has *137 mains, and soon to be *140 as the main jets.
The carb tops are exactly the same, so no restrictions there.

Note: My replacement rack came from a USA  A6 Model.

The NEW Rack of CVK34's from an A6 (USA Model).

The airbox on the 1984 is opened on both sides of the intake - at the rear
of the airbox, whereas the 1990 A7 airbox is closed completely on the
left hand side of the airbox. I estimate this restriction to be almost a 55-60%
reduction in the airflow capacity - based on simple measurements.
This is the other part of the de-tuning of the A7 model.
I have replaced part of my airbox using the earlier model rear plate.
This is still available from your Kawasaki dealer but was ordered from Japan.
You only fit the earlier model rear plastic plate, not replace the whole airbox.

My original Airbox.
I modified the rear-plate to allow increased air flow. I added the two ports on the left side.
However I now have fitted the original A6 plate - seen below.

The Original A6 model Airbox plate.

I have a K&N high-flow 'lifetime' cotton filter (K&N KA-9084) to fit into
the original airbox - available in US and UK - not AU.
I bought mine via Amazon website. About the same cost as OEM filter.
These are washable and re-oilable, and provide a massive increase in
airflow over the standard filter.
Lifetime warranty, so never buy another filter.

I have a 40mm 4-2-1 high-flow aluminium exhaust system. (right side)
This is a Magnum original, setup for GPz900R (92DB). Better flow,
power and economy. And no Rust !
This will soon be replaced with a new stainless steel 4-1  52mm
exhaust system. (right side)
I bought this via Tony at Barracuda exhausts (see Web), because
no-one in Australia has a ready made GPz900R SS exhaust and quotes
to make one were over $2500 Aud - which in my opinion is ridiculous.
This is an absolutely beautiful system, and is made in Germany.

The Barracuda 52mm SS exhaust system to be fitted.
The muffler also has a removable baffle for racing.

The air-flow mods are the reason for the main-jet size increase.
It is an educated and measured guess without dynotuning.
And as my bike will be only for road use, I dont mind the in-exact
science of jetting based on real world road-riding, and then set the
jetting accordingly.
I will fine tune this over time, however it takes a fair bit of effort
to change jets and find the best main jet for full power.
Then adjust the needle height to match. And float height as well.
I may still get it dynoed.
See Jamie at S&R Pro at Penrith (Sydney) NSW.

I have chosen to retain the Keihin CVK34's as my preferred choice
of fuel delivery. I like the way CV carbs work.
When setup properly, they give a good balance of power and economy.
I know some people prefer flat-slide carbs for a bit extra power and
the instant throttle response they give, but if my ZZR1100 can run
160bhp from its CVK40's, then I think the GPz900R will be happy
enough with its CVK carbies.

And get NEW Carb mount Rubbers if you are replacing your
Carb Rack. It is worth it.
The original ones will be as hard as a rock, making it almost
impossible to reseat the new Rack.

When rebuilding carbies, some o-ring and other rubber seals are
quite dear to replace. Especially on a rack of 4 carbs.
I took some advice from a webite that said you can soak the o-ring
and float-bowl gaskets in acetone overnight.
They will soak some up then when left to dry they will shrink back
to original shape and thickness.
If you have any torn, cracked or worn seals you should replace them.
Make sure you get o-rings that are suited for petrol use.

I also bought braided lines for my brakes.
This is an obvious upgrade to any hydraulic brake system.
Old lines expand among other issues.
You may wish to see my http://bleedingbrakesklr250.blogspot.com 
Blog about trials of bleeding brakes and a nice vacuum bleed method.
Unfortunately Australia was limited in options to have lines made,
quotes were almost 4 times the cost of a complete delivered set.
So I got them Online from Wez - at Wezmoto in the UK.
They are great however I did replace the banjos with a nicer looking
option - for cosmetic reasons only. From Venhill in UK.
Note: The UK has a lot of GPz900R's roaming around,
so parts are readily available.

I have just bought a pair of Hella twin-DB horns. They are small,
and are trumpet styled and will replace the original rusted horns.
(from Amazon US as Australia did not have these models)
I assume they will be loud but have not wired them up yet.

I do need to replace the radiator.
I will look for an increased capacity and flow aluminium model.
Nothing is made for the GPz900R that I can find.
Such it is with old bikes.
Once I find something, or get something made, I will update you.

3. My Choice

My Choice - The Kawasaki GPz900R.

There are several reasons for me choosing the Kawasaki GPz900R
as my project bike.

I have been road riding since 1980, and trail bikes and minibikes
back into the 1970's.
I have seen some great changes in motorbike tech over the years.
Not just power, but handling, brakes, fuel injection, wheels & tyres, etc.
Everyone has their own idea on what a motorbike should look like.
Some people just love cruising, some love fanging around,
some love racing, some just love machines.

But we all love a ride.
- the freedom.
- the fresh air. (mostly)
- the sound.
- and the simplicity.

Me, I love to ride, but I also like the time in the garage, just tinkering.
Pulling things apart and putting them back together.
I do this with cars and motorbikes, pushbikes and scooters.
So, for me, I also want to be able to enjoy my hobby.

That's where the GPz900R comes into the picture.
It is a bike with simple technology, but nevertheless it has some
quality about its design and its components.
Although I like some older bikes, like Vincents, Triumphs,
Motor Guzzi and of course Ducati's, and I really like the TC88 Harley
engine (maybe see myself with a Deuce Softail one day), what I wanted
was a bike that still had most of the advancements of a modern bike,
like good brakes and wide tyres and a bit of grunt when required,
but I needed something with older technology like carbs,
and screw tappets, and gravity fed fuel tanks, etc.
Something I can do most the work on in my own garage.
I have always loved Jap 4's.
The sound, with the right exhaust.
And smooth power, and plenty of it.
And reliability for day to day use.

I have owned,
a     Kawasaki ZX10, and KLR250,
and Suzuki     DR250, and GT380,
and Yamaha   XV1000 (TR1),
and Honda      XL500.

And for a time ridden a,
Motor Guzzi LeMans 5 1000, Honda Bol'Dor CB900R,
Ducati SD 900 Darmah, BMW K1000RS 1985.

I rode my fathers Suzuki's.
I learned to work the clutch, and good balance, on his A100.
I rode round and round the backyard until it was 2-stroke blue.
And down to the local bush reserve dirt trails for quiet rides.
Then I got my licence on his Suzuki GT185, which I then
had to learn traffic survival.
The GT185 was a really great little 2-stroke.

And as a teenager I used to ride my friends Suzuki RM80,
and Yamaha YZ80G, and a Suzuki A80.
The trail bikes were used to play 'tag' on, so some good handling
techniques were learned here.

And of course as a kid, I rode mini-bikes.
These had auto-clutch setups.
Some were even zip-start engines.

Well the choice was finally made.
I would search out a Kawasaki GPz900R.
It ticked all the boxes for what I wanted.

So, I found myself a Kawasaki GPz900R A7 1990, in September 2010.
A bike 20 years old, with just under 100,000km on the clock.
In complete condition, but a bit rough.
It had been neglected.
Even though garaged, it had dry joints and some coroded wiring.
It has a 'creamed' tank.
Crappy seat.
Slightly bent right handlebar.
It had been used on track days.
It had been dropped.
And had been repainted, and had the fairing rebuilt in places.
BUT, It was straight. It was complete.
I knew what I was getting.
And I knew I could fix, repair, and restore it.
It was the 1990 model so it had a 17" front end, 41mm forks, and
twin-piston Tokico caliper 300mm brakes.
And non-return CAM tensioners.
From what I could tell, someone in its past had actually looked after it.
It had a nice 4-2-1 aluminium Magnum genuine GPz900R spec exhaust.
It had new Metalgear brake rotors and new pads.

It did need some TLC.
And now, it was mine.

2. A Brief History of the GPz900R

1984:

Most of below is taken from a few selected Web pages - with gratitude.
I have added my opinion, and some updates about my specific bike.

The original bike was released in 1984.
It was groundbreaking in many engineeering respects, and a showstopping bike in
looks and performance.
And, according to sources, the first of its kind, for a production bike for many
technological reasons.
It is considered by many people to be the grandfather of the modern sportsbike.

Firstly, it uses an inline-four configuration which is Watercooled.
It has a 4-valve head.
It has Double Overhead CAMs, and a side mounted CAM chain which reduces the
width of the engine.
This type of engine configuration seems to be settled on as the 'norm' for many
modern sportsbikes today.
And is used in race bikes like the MotoGP, 600's, and Superbikes.

Secondly, It uses the engine as a 'stressed' member in the frame.
It was found that the lower downtubes, using this particular 'spinal' frame design,
dont contribute much to the torsional frame strength, so they were eliminated.
This allowed the engine to be mounted quite low keeping the centre of gravity low.
This greatly improves the bikes handling while maintaining high cornering clearance.
Even though it is a steel spine frame, and many bikes now use aluminium twin-spar
type frames (which are more rigid), some modern bikes are using the same principle
for frame technology today.

Opinion:
The bike has a definite solid road feel. It feels very 'planted'.
The bike also is very forgiving when road conditions become unstable, and has
almost no wandering or flex in the frame.
I am not sure if this is due to the frame design, or maybe because the whole bike
geometry is just well sorted.

Update:
Even though the original 1984 model had a 16" front wheel (120/80/16) with
anti-dive 38/39mm diameter forks, and a relatively narrow 130/80/18" rear, a
setup that worked quite well and was part of the appeal for a 1984 sport bike,
improvements were to come, as the industry again settled on standards for
handling and performance of modern machinery.
The A7 model has a nice fat 3"(wide) 17"(diameter) front Enkei wheel
with 120/70/ZR17 rubber.
The A7 rear was increased to a 150/70/ZR18 tyre and the wheel was 3.5"(wide)
18" diameter Enkei wheel.
The A7 also got rid of the anti-dive fork system, which I am led to believe
worked quite well, if maintained, and upgraded its forks to 41mm units, with
heavier progressive springs.
According to sources, the GPz had better handling with this front end setup.
(although I cannot make a personal comparison)

Thirdly, It has some great brakes.
It has a triple disc setup with drilled solid mounted rotors. Nice for a road bike.
The front pair are 280mm with strong single piston calipers.
The rear is a 270mm (maybe 280mm) also with a strong single piston caliper.
This allowed the bike to be ridden harder and faster, and with more confidence,
as it could now stop as well as it goes.

Update:
The A7 model upgraded the components to 300mm front 'floating' discs with
twin piston Tokico calipers.
And the rear is now a 250mm disc with a twin piston Tokico caliper.
They are reasonably light to touch, give a good controlable progressive feel,
and they do stop very very well.

Fourthly, It has a great 6-speed gearbox.
I am not sure how many bikes at the time had a 6 speed box, but it seems
common nowdays.
Changing gears is quick and reliable.
However a 'false' neutral can still occur on rare occasion.
The gearbox does give you confidence in its gear selection.
Given the wide engine power band and many gear selections, you always
have enough power no matter what gear you are in.

Opinion:
The bike also accelerates hard in any gear, and can do 6th from about 2800rpm
very smoothly.
Redline is 10500rpm. (and spins there without complaint)
Gearing on my A7 is about 25kph/1000rpm or 4000rpm at 100kph in 6th gear,
using the (150/70/ZR18 Michelin MACADAM)
 - 5th is 22kph/1000rpm.
 - 4th is 18kph/1000rpm.
 - 3rd is 16kph/1000rpm.
 - 2nd is 12kph/1000rpm.
 - 1st  is 10kph/1000rpm - and you can do 0-100kph in 1st gear
                                        in about 3 seconds flat.

NB: The 17" rear has me at about 102kph at 4000rpm in 6th gear, running
a 160/60/ZR17 Dunlop SportMax.

Fifth, It looks great (and very cool).
It rides really well, its engine is smooth, and it has a nice balance for a
225Kg (dry), maybe 250kg(wet), Streetbike.

Other things I have read and noticed:

 - Counter balancer on Crankshaft - minimising engine vibration.
 - Top-mounted starter motor.
 - Water-cooled - however it does use its thermo fan a lot when stopped,
   and in low-speed traffic.
 - Full fairing - increased aerodynamics for greatly improved high speed stability.
 - Good ergonomics - making it enjoyable for daily use, and long rides.
 - Good Screen - does the job well.
 - Great fuel efficiency - has a large 22lt (4.8ImpGal) tank capacity.
   Opinion: I have achieved 65mpg (23km/l) while touring, without trying,
   at upto 80mph (130kph).
 - Good low speed ability - engine performance is tame at low speed,
   and great agility in traffic.
 - Amazing acceleration - a sub 11 second 1/4 mile time in street trim, in 1984.
 - I am told it will crack 150mph (or 240 kph).
 - An engine in 1984 with 115bhp (engine), and A7 has 108bhp (engine).

1. 17" Rear Wheel Conversion for GPz900R - 1990 A7 Model - The Beginning.

I am the proud owner of a GPz900R.

I chose this bike because I wanted a project.
I chose this bike because I wanted something familiar.
I chose this bike because I wanted history.
I chose this bike because I wanted a Kwakka !

I currently have a GPz900R and a ZZR1100.

My ZZR1100 is a 1999 D7 model.
It is pretty much stock.
Although I added a nice leather seat, braided brake lines and K&N filters.
It doesn't need to be any better.
It goes like stink, handles extremely well for a heavy bike,
and tours effortlessly with style and efficiency.

My GPz900R is a 1990 A7 model.
It has done just over 100,000km's.
It has been used on track days.
It has been neglected.
It has the wrong paint.
And it has been patched up from some drops.

However...
I still bought it.
It is complete.
It rides true.
The frame and wheelbase measured straight.
It has a genuine GPz900R spec 4-2-1 Aluminium Magnum Exhaust system in good condition.
It has new MetalGear brake rotors and pads.
And the A7 model has all the good bits.
17" front wheel, 41mm forks (no anti-dive), dual-piston calipers all-round, and 300mm
floating front discs and a 250mm rear disc brakes.
Non-return CAM tensioners.
And although this model is de-tuned a bit, we will endeavour to address that.

So...
A nice rebuild/restore project awaits.
I have no rush, and will do each step slowly as time and cash permits.

My ZZR1100 D7 - 1999.

My GPz900R A7 - 1990.