nr's blog

King Of The Swingers 14 September, 2014

Filed under: Motorcycling — nr @ 10:57 am

As previously mentioned, one of my goals with Project Adequate ZXR is to try and lose a bit of weight. There’s nothing actually wrong with the stock H1 really, but it’s a bit of a heavy old porker. And one of the areas that just seems to scream out for a bit of attention is the stock H1 swingarm. Really, it’s horrid. It looks like it was bodged together by a first year agricultural engineering student out of box section steel, and when it turned out to be a bit bendy, they just welded on a couple of big plates and a whole second layer of superstructure. Really, it’s horrible, and I reckon about 6kgs overweight. So, I decided to try to do something about it… I picked up a swingarm from an H2 model from eBay, and by the time I’d scraped off 25 years worth of road muck, I was able to measure it up. The good, and not entirely unsurprising news was that the length was close enough to work, and the width at the pivot end and mounting of the shock linkage were spot on. So, I enthusiastically set about doing absolutely nothing with it for six months while I got on with some weapons-grade procrastination instead.

Eventually, however, the time came when I had a spare day, and no excuses. So, I rigged up an entirely unsuitable and dangerous way to support the rear end of the bike while I worked on it, and came perilously close to losing a couple of fingers when of course it didn’t work. Champ then came to the rescue with the simple idea of using a couple of axle stands under the rear part of the frame, which of course was simple and worked perfectly. The old swingarm came out without a fuss, and with suitable lubrication, the new unit was swiftly slipped in from behind. The only fly in the ointment was that Kawasaki changed the bearing spacers inside the pivot between the H1 and H2, and also changed the pivot itself. It’s not a big problem, it just means that the pivot sticks out about 7mm more on the right side now. I’ll look to getting the shoulder of the spindle machined down at some point in the future. But for now, it’s in, and it works. Or so I thought…

While I had everything in pieces, I also thought it prudent to fit the NWS suspension rocker that I had kicking around. These little thingies are brilliant. Early ZXRs had a reputation for having very unforgiving ride quality, which was fine on a smooth racetrack, but bloody uncomfortable while pottering around The Fens, or practically any other road in the UK. There were several proposed solutions to this, but the best, I reckon, was when NWS changed the geometry of the rocker – I had one of these on my first couple of ZXRs, so was more than happy to pick one up for this one, given that they were pretty rare when new, and almost impossible to find now. And while I was doing this, it made sense to replace the bearings in there too – NWS had the foresight to use standard size bearings, rather than using the Kawasaki OEM ones, so replacing them all cost the princely sum of 12 quid.

So, once it was all nailed back together, it looked like this:

P1050171

Which, other than obviously needing a bit of a clean and polish, looks OK. And more importantly, saves about 6kgs over the stock setup. Job done, you’d think.

However, all wasn’t sweetness and light… One of the primary rules of messing with motorcycle suspension is to change one thing at a time. I totally ignored this by changing the swingarm, rocker, shock, and crucially, tie-bars all at the same time. The tie-bars were swapped out for some slightly shorter items to raise the rear ride height a bit. I’m not sure that the ZXR actually needs this, but it’s something I wanted to try out. In stock trim it’s outstandingly stable, but a bit slow to turn, and the normal way to improve this is to raise the ride height. All looked good, until I realised that the torque arm was now clouting the exhaust at full extension. I scratched my head for a while, before looking at some old photos. Particularly, this one, of Scott Russell’s AMA winning bike:

ZXR1

You can see that the torque arm is connected to a lug on the swingarm, rather than the normal location, which is that little hole below the swingarm pivot. No problem – a quick message to the marvellous Spike, at Cambridge Motorcycles revealed that he’d be happy to modify my swingarm with a small lug. So, I picked up a new torque arm from eBay for three quid in readiness for this. And of course, Mr. Kawasaki had the last laugh, as I picked up a torque arm for an H2 rather than H1, and for some stupid reason the bush in the rear caliper is a different size between the H1 and H2, so it doesn’t fit. I have absolutely no idea why the H1 was built in this way, as the wider bush allows about 10mm of lateral movement of the torque arm. So while I’m getting the swingarm modified, I’ll also take the opportunity to take a few mm off of the bush. It’ll save another gram or two.

But, for now, it’s all good really. I popped out for a ride around Suffolk/Norfolk yesterday on some of the back roads of my youth, and the ride quality is way improved over when I picked the bike up. I suspect that 99% of that improvement comes from the NWS rocker and replacing the bearings, but still, I reckon I’ve saved a good 6 or 7 kilos by swapping out the swingarm, and another 3 or 4 by using the single seat unit and losing the rear footpegs. Also worth mentioning that the rear end also looks a lot cleaner now. I’m not going to fit a hugger, as I don’t think it needs one. I’ll bodge together an undertray to keep the electrics dry, otherwise I know I’ll end up sitting by the side of the A142 in a monsoon with a dead bike at some point in the future.

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4 Responses to “King Of The Swingers”

  1. Ian Crossley Says:

    I last replied to your blog in January,I was having carb problems with my H2.Anyway your bike looks good now you’ve got rid of that old swing arm.Have you done anything with your brakes yet because you mentioned something about a nissin conversion kit,because like you I’m not entirely happy with my brakes even though I’ve got used to them now ,a little more stopping power wouldn’t go amiss though. Have you had any alternater belt issues,I’ve broke 2 belts and am now on my 3rd which seems to be holding up pretty well thanks to the purchase of a belt tension tool. So now I’m just enjoying life as a motorcyclist again and loving it.

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    • nr Says:

      No problems with alternator belt so far. Touch wood… As for the brakes, yup – still planning to convert to Nissin four-pots when I have some spare pocket money. The Tokicos are kind of OK – but I’m pretty picky about brakes. There’s no shortage of power, but I don’t get much feedback from them. I used Nissins on my old TZ250 and endurance GSX-R, and they just felt a whole load better. I guess I’d best start saving… The ZXR has just gone into the garage for the winter strip and rebuild to sort out the swingarm spindle and a few other bits and bobs, so I may well swap the calipers while I’ve got it in bits. Watch this space 🙂

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  2. jbretel Says:

    Hiya, I also have a 1989 ZXR750 and have been trying to locate an NWS shock linkage – or have one fabricated. Would it be possible to get accurate dimensions for the new linkage, from yours please? – ie the spacing between the holes (in mm measurements) so I can put it into a cad design and have one fabricated (maybe more for other ZXR H1/2 forums members.:-) ) Many thanks – Jeremy my email is jbretel@cwgsy.net and mobile 07781 430976.

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