By Vince2
#101371
Hi, with the bike static the front forks look to short but length of the springs is correct. Can springs lose tension without reducing in length? Vince
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By stinkwheel
#101372
Only if they were badly made springs. So yes.

You could try bumping up the proload by fitting a spacer on top of the spring (slices of blue plastic waterpipe work well) but this will only work up to a point, if they are becoming coilbound at full compression, they just aren't powerful enough. Another bodge I've seen was to space out the spring with old valve springs, same applies though.
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By stinkwheel
#101386
I suppose the thing to take from that is spring length isn't everything and manufacturers stated suspension settings are just a starting point. A Redditch bullet will be no different to a modern japanese sportsbike when it comes to setting up the suspension, just with fewer knobs to fiddle with. The main thing is getting the static sag correct and it sounds like yours is far too high. So you either need a longer spring, a stronger spring or more preload (or a bit of all three). Or simply a progressive one.

I suppose the difficulty will be sourcing springs with different rates. I'd suggest finding a modern bike with a similar weight and geometry and plugging your own weight, luggage and riding style into one of the spring rate calculators (racetech have an online one). Then it's finding a more modern bike with springs the same diameter and similar length and ordering a set of the appropriate rate. Slightly too short is probably better because you can always add spacers.

Once you have the correct spring rate, you can work on altering the preload with spacers to gain the required static sag, which will be less than most modern bikes due to the smaller length of travel.

Once the rate and sag are correct, you can fiddle with damping, which will be down to air gap and oil viscosity with a Bullet, unless you want to start messing with damper rod shim stacks -which you don't.

For YSS springs, the part numbers go like this:

L or P for Linear or Progressive
R for Road
290 for 29.0mm outside diameter
I for standard shape
xxx for three digits indicating linear spring rate (or higher spring rate for progressive) in N/mm. So 095 would be 9.5N/mm
- if using progressive springs
yyy for three digits indicating lower spring rate for progressive springs in N/mm
S for indicating spring material
zzz for three digits showing spring length in mm.

So they list springs for the Electra as PR290I055-095S520 Which is a progressive spring, 20mm OD, 520mm long with a rate of between 5.5 and 9.5N/mm.

From a brief look, assuming the older bullets also have a 20mm OD/520mm long spring, you could use springs for an 88-90 GPZ900R, although standard ones are actually softer than the bullet ones

I'd try spacers first though.
By Vince2
#101524
Hi, I noted that when the oil was drained from the forks the static level became correct. So it appears that some kind of hydraulic lock is preventing the forks from fully extending. Any ideas? Vince
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By stinkwheel
#101526
As far as I know they are damper rods with a valve with holes in at either end that get alternately covered by a plate depending if it's on a compression or rebound stroke. So I'd imagine for it to get stuck in compression, either the holes are blocked or the plate is stuck down on one or both valves.
By Vince2
#101533
Hi, thanks for confirming what I suspected. Compared to my spare set of internals the discs are very stiff even though oily. Vince
By Vince2
#101708
Hi, after much fiddling it transpired that one spring had gone soft, so the other spring was taking all the weight. Replaced with a spare spring and all ok now. Just to clarify these are the early forks with steel sliders. Vince

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