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Progressive fork springs or not

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Al
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#46 PostAuthor: Al » Wed Aug 10, 2016 11:09 am

A year on, thought it was time for an update.
Been at Odiham, Oulton Park, Spa and Cadwell and there have been some changes albeit slight but due to some incidents, unforseen circumstances and natural developments, some adjustments have had to be made.

Bearing in mind that these settings are for track use i am posting to highlight the subtleties in changes, to give an indication of how much difference, small adjustments make with this set-up.

The original set-up, once it was initially in a place that was suitable.

Rear rider (full) sag 12.5 mm
Front rider (full) sag 37.5 mm
Fork main spring pre-load 5mm (equal to the minimum recommended)
Emulator valve springs Yellow (64 Lbs / inch)
Emulator valve spring pre-load 3.5 turns.
Fork oil 20W (True S.A.E.)
Oil level is 135mm bottomed with springs out and emulators in.
16 mm of fork top leg protruding through the top yolk.
Front tyre pressure 33 PSI
Rear tyre pressure 29 P.S.I.
Tyres Conti Attack CR2
Weight at front wheel 105 KG
Weight at rear wheel 106 KG.

Settings now. Changes highlighted in red.

Rear rider (full) sag 12.5 mm
Main linear springs Bike sag is 26mm Front
Rider sag (full) for both bike and rider) 37.5mm
Fork main spring pre-load = 11mm, achieved with several plain washers above the plastic tubes.
Emulator valve spring pre-load (Yellow 64 Lbs) 4 turns from just open.
Oil weight 15W (true SAE) I'm likely about to change back to 20W
Oil level 120mm from top of tube, compressed fully, springs out, emulators in.
20mm of fork leg sticking out above top yolk.
Air pressure = zero when bike on wheels.
Front fork full travel under full brake was 3 1/4 inches


Everything else not highlighted in red stays the same. You could say that those items which are highlighted are the ones that make the most difference or that they are the ones that will never be right to satisfy different criteria. Eg. different tracks or differing conditions.

Dont think i posted the part numbers for the bits i have fitted either;

Valves; FEGV S 3501
Linear springs; FRSP S 2938 (0.95 Kg/mm)

These are in standard J forks / standard J yolks.
Emulators would likely be the same number but spring rate would differ depending on various things like bike and rider weight / intended use etc. etc.
I could see a possible problem with 1100 B forks / yolks / bars in that i think the bars hold the upper legs to a given fixed height. I think that may end up with the front end riding too high but not sure if that can be got round somehow with maybe a tubular spacer outside the stauntion.

Anyone been playing with these on a road set-up??

AL
Last edited by Al on Wed Jun 28, 2023 10:26 pm, edited 1 time in total.
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Fred the Zed
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#47 PostAuthor: Fred the Zed » Wed Aug 10, 2016 7:53 pm

Great info Al.

Mods and changes mapped out brilliantly. Will the same part nos fit other Zeds... Z1R for example? I need to sort the seals on my 78 Z1R so I might as well change the springs and oil and try the emulators out.

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#48 PostAuthor: Al » Wed Aug 10, 2016 8:57 pm

How ya doing Fred?
No not those numbers for the Z1R. They divide the series down into sets and yours would be included in the Street, Kawasaki, KZ1000, 1977 to 1980 collection.
Not being patronising but those are the selections you need to make from this page

http://www.racetech.com/VehicleSearch

http://www.racetech.com/VehicleSearch#g ... ar=1977-80

Think it said 36mm forks for the 1R, where the J ones are 38mm.
It looks as if the Shed may need some "Fork Emulator Adaptors" AD 3003 P.
But i would really speak to them to confirm this first.

If youre sure about what you want then fine but they list spring rates for about six or seven different needs!

Mine are 50% stiffer than standard from 0.65 Kg/mm to 0.95 Kg / mm.

Shout out if i can help. When i opened the spring box the last thing i expected to see was a bit of thick walled plastic tube!!!!!!!!!!!!!!:shock:

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#49 PostAuthor: Fred the Zed » Sat Aug 13, 2016 1:18 pm

Cheers Al!
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#50 PostAuthor: Fred the Zed » Mon Oct 31, 2016 10:56 am

Time for an update on Zorded's great thread...

I've eventually got around to ordering the bits and pieces from PDQ for my 78 Z1R..

As I'm a hefty bear at 16st odd:

0.85kg Springs: FRSPS 2341085

Adaptors for Z1R: FEV AD3003P

Emulators: FEGV S3001

All in, including postage was a total of £296.05. (But prices about to go up)

3 week wait for the parts from the US. :roll:

Race Tech reckon 15w oil.

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#51 PostAuthor: Z1parR » Mon Oct 31, 2016 10:51 pm

Nice one Rich :up
Thanks for sharing your findings and experience .
0172 . Geoff Parr

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#52 PostAuthor: Fred the Zed » Tue Nov 01, 2016 9:50 am

Z1parR wrote:Nice one Rich :up
Thanks for sharing your findings and experience .


Its what makes the Z1OC world go around. :D
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Re: Progressive fork springs

#53 PostAuthor: Coose » Fri Jun 09, 2017 6:56 pm

Following up from All's post above, we've been in conversation over the last few weeks (months maybe?) about forks and stuff, where I assumed mine were stock and ok with a little air, but air in forks is not right as it's too inconsistent.

So, last week I ordered some 0.9kg/mm Racetech springs, and found out that YSS make a direct copy of the Racetech emulators but for £67 from Wemoto! You can find them slightly cheaper elsewhere, but Wemoto keep them in stock and were kind enough to quickly confirm the dimensions.

So today I threw it all together, using Al's settings as a benchmark: -

Preload: 15mm (I can shorten the tube if necessary).
Oil: 15w Silkolene, 120mm gap (emulators in).
Emulator setting: 4 turns out of 7. There is only one spring with the YSS valves and I'm unsure of the rate.
Damper rod: 6no. 8.5mm holes drilled.
Fork springs: 0.9kg/mm.

I tried to measure the sag but it was a little hit-and-miss due to new bushes, but it seems to be around 30mm static and about 45mm laden. So, a bit more than Al's as expected, but more on this later in the test-run report...
I'll get a few more miles on it and will measure again.

Now the important bit. I started riding through town towards one of my usual test routes and immediately noticed the difference. The roads around here are shocking, but now I have high-speed damping control and barely noticed the bumps!

Riding out of town I overtook a car and it properly shook its head as I crossed the crown in the road. So, I wound up the steering damper, which masked the problem beautifully.
So, down one of my favourite wiggly bits and it felt great, though still nervous. I stopped and let a little air out of the front tyre to make it less pointy and straight away I could back off the steering damper a little, though it was still lively.

I then headed for my local test track, which is awesome but the surface is terrible - it looks like a farmer had dragged a plough over it!
What I did find was that I could just pin it and I didn't notice the horrible surface, so a massive improvement! I stopped to contemplate, dropped a bit more air out of the front, which solved the problem and I could then back the steering damper to where it was.

I got home, let the tyres cool and found I still had 34psi in the front! I then dropped this to 32 and I'll see how it goes. I'm not sure how much was originally in there, but I must have been drunk when I pumped it up... :wink:
Though, on standard forks it felt better with a higher front tyre pressure.

So, a massive improvement for not a great deal of money. It's always going to be a compromise, it doesn't handle like an R1 but it never will and I don't want it to! :)

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Re: Progressive fork springs

#54 PostAuthor: Al » Thu Jun 25, 2020 10:42 am

Looking at replacing the original pics which were posted in Photobucket but are now absent so found these instead.

Small hole
RIMG0016.JPG


De-burr larger hole
RIMG0017.JPG


De-burr internally with a length of studding
RIMG0018.JPG


Clean up externally
RIMG0020.JPG


Cut spacer tube to length
RIMG0021.JPG


Order of assembly
RIMG0022.JPG



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Re: Progressive fork springs

#55 PostAuthor: Al » Thu Jun 25, 2020 11:15 am

APPLES AND ORANGES. Been sitting on this for a while but due to the cancellation of trackdays to date have not been able to evaluate any changes.
What i can say is that mistakes have been made!! Figures are tiny but the two i highlighted rows show the approx range i was working in. What eventually became apparent with the appearance of this chart,... Thanks Brian 1100R and Mr Mahonkin, Peter Verdone, was that Silkolene (my chosen manufacturer) used not to have a continuity policy through their range of Pro and standard fork oils.

I assumed wrongly that they were interchangable when it is clear that they are not / were not. I believe they have now settled on a single viscosity index between the two product ranges!!!!
Looking at the two highlighted rows you might notice that initially: Pro RSF 10W is twice the viscosity of their 15W listed immediately below when at 100 deg. C but the same at 40 deg. C.
Its the same for V.I. when re-calculated.
Its not until you get to V.T. and divide the 40. deg. C value by the upper range at 100 deg. C, that things start to be the right way up.
From a practical perspective; i had used say 10W and believed it to be 'too thin'. Then changing to what i believed to be a higher viscosity (15W) gave a very different set of problems, complicated not least by the fact that the viscosity changes with temperature and at some point along that temperature change they switch sides!!!! :??
That represented about two seasons of head scratching and a great deal of fork oil changing!

Looking down the list its also easy to see that for this example; Silkolene Pro RSF 15w is twice the viscosity of Silkolene 15W fork oil :oh

The full list in full size is available from the link at the bottom. Or you can click to zoom just this selection.

Oil weight range.png


http://mahonkin.com/~milktree/motorcycles/fork-oil.html

ISo grade oil vs Cst.jpg
ISo grade oil vs Cst.jpg (51.62 KiB) Viewed 7319 times


AL
Last edited by Al on Fri Jun 30, 2023 2:37 pm, edited 1 time in total.
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Re: Progressive fork springs

#56 PostAuthor: Al » Sun Nov 01, 2020 10:37 am

A couple more thoughts; I had been aware for a good few years that the very early J forks had only one pair of rebound springs and that later versions had two pairs stacked one above the other. I had failed to see the significance of this and had just assumed that rebound was rebound. I bought a pair of B model forks recently (thank you Scott) and they had the four spring arrangement as per standard for that model. One of the issues with my fork set-up is that; under hard acceleration, particularly out of corners, the forks would hyper extend. This changes the steering angle and the rake and trail characteristics at precisely the point where it is most critical. "fastest rider is not the one who gets on the throttle first its the one who gets to full throttle first" Un-quote etc etc etc. These extra springs resolve this issue to some considerable extent. Clearly an issue that became apparent after release of the first model J's.

There has been some suspicion that at the point of initial bite of the front brake and the moment of the onset of compression of the forks that the up-rush of oil through the old damper rod; lifts the emulator off its seat for a fraction of a second as the oil would rather go round it than through it. On 100% full front brake the forks would oscillate / spasm momentarily.
Coose was looking at machining a groove in the emulator body and turning up a pair of the nylon 'piston rings' as per the damper rods come equipped with. This would oblige the oil to go through the emulators and not try to go round. However it seems he was not the only one to have that great idea.


Emu piston ring adaptors.png
Emu piston ring adaptors.png (79.92 KiB) Viewed 16460 times



These particular ones (above) are not listed for our bikes but since some models (Z1R etc) need an adapter to correctly seat the emulators i can see no reason why this version with its piston ring could not be made to fit in its place or retro fit to J forks that dont need the spacer but would benefit from greater control of the oil flow. I will make some enquiries to find out a bit more about them and their availability / sizes etc.

AL
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