PROJECT NINJA
Rob has been working hard on the ZXR750.ZXR750 This month he’s been busy with the shock, linkages and exhaust system.
I t’s time for a bit of a progress update on my Z X R project and things are moving along fairly quickly. After getting the swingarm fitted last time I could start to think about the shock and linkage arrangement. I had already acquired a ‘new old stock’ (that’s what NOS means on eBay apparently, nothing to do nitrous) FOX Racing shock. G iven that these were made in the early 90s my first job was to give it a good once over and take it into work for a re-gas as it was bound to have made an escape after 2 5 odd years on a shelf. Everything was still spot on though and I filled it up with 400psi worth of nitrogen during my dinner break. I could try to sound clever and say I went for nitrogen because it doesn’t have as high a coefficient of heat expansion as fresh air so the shock will work better even when warm, but the truth is, it was just what was in the bottle. I bolted the shock in and also cleaned up and re-greased the original H 1 linkage.
The original dog bones weren’t going to work with the new swingarm, and as the bike is going to see some track action when finished I decided to make some adjustable ones which will allow me to play with the geometry later on. I’ve made these linkages quite a few times before; it’s pretty easy and relatively cheap to do (less than £40) I got four M12 Female Rose J oints, 0.5 m of H igh Tensile threaded bar, some M12 H alf thickness nuts, M12 penny washers and new slightly longer linkage bolts (rose joints are thicker than dog bones). Then it
was just a case of working out the length of rod I needed, cutting a bit of threaded bar putting two nuts on it, then a rose joint either end, the trick is getting a decent and equal amount of thread in each rose and leaving a bit of space for adjustment. When I was happy I put a bit of heat shrink over the bar in the middle just to make it look a bit posher and did another one and set it the same. Fitted with the longer bolts, I think they look pretty trick.
Next job was trying to get my tired old Vance and H ines Supersport Exhaust system (which has sat in the back of my cave for about eight years gathering dust) looking a bit better. First task was to strip off the old heat wrap which just about fell off on its own.
Underneath the pipes were still solid but had furred up fairly badly. A good hour or so with a wire wheel in my drill had all the rust successfully transferred from the pipes onto my face. After a few coats of barbecue paint from my local hardware store they were looking almost as good as new. I think I will thermal wrap them again soon before fitting.
With forks and a swingarm properly in place, I turned my attention to the wheels. I have gone for a set from a Z X 9R C model, mainly because of the huge weight saving over the original Z X R wheels (which I am sure are made of depleted uranium) but also because they are easy and cheap to get hold of and the three-spoke pattern is in keeping with the late 8 0s style which I am going for – more modern wheels wouldn’t look right. I had them powder coated white at the same time the frame was done, chucked new bearings and dust seals in all round, and fitted the G alfer wavy discs and a spacer plate I acquired ages ago to the rear sprocket carrier, which gives the correct offset when using the later wheels in earlier Z X Rs. The rear fitted in easy enough, with clearance either side when the wheel is central. The front fits pretty well too, I’m just waiting on some aluminium to arrive up so I can turn up some spacers and make a hangar for the rear calliper;
I can’t use the standard one as it is a bit too thick to fit. But the most important thing is that it now looks like a proper motorbike not just some metal bits.
Not wanting to sit idle while waiting for bits I did a few other engine jobs, cleaning and painting the gearbox cover, engine breather and sump. I stripped, checked, cleaned and fitted the water pump and alternator complete with a new belt (yep that’s right, how 8 0s, a belt driven alternator) and also got a clutch in there. A cool, and relatively unknown, thing about all Z XR 7 5 0s is they all come from the factory with a slipper clutch fitted, it’s just set up not to work (factory fitted slipper clutch in 198 9, way ahead of its time). It is activated by changing the stack height of the clutch pack, using different thickness of steel plates, to allow room for the slider to move and then changing the strength of the springs to get the desired amount of slip.
To begin with I am going to stick with a new stock clutch until the motor has been set up and proven so I know where I am with it. Once I’m happy with things, I will have a play with getting the slipper to work as it will be needed with extra engine braking from the big bore high compression motor and more front bias weight distribution the bike will have.
That about wraps it up for this instalment. By next month I should have the wheel spacers done, brakes sorted, exhaust, carbs, oil and cooling system all fitted and if I get on well enough I may even make a wiring loom too. If I do get to that stage there’s no reason I won’t be able to have it running, exciting times.
I HAVE GONE FOR A SET FROM A ZX-9RC MODEL, MAINLY BECAUSE OF THE HUGE WEIGHT SAVING OVER THE ORIGINAL WHEELS