How long should the fork springs be?

[sonic]

Finally got the time today to fit my Hagon Progressive fork springs and have come across a little problem. (1980 model)
The springs that came out are 485mm long, and are progressive wound.
The Hagon progressive springs are 520mm long and as per their instructions, when the forks are on the top of their travel the spring protrudes about 15mm. You couldn't see the old springs in this position.
I can't get the fork cap back on, it's fairly long as it's the three stage adjuster type.
Does anyone know if the 485mm springs are the correct standard length.
Also when I took the springs out, they were in with the tight coil at the bottom. Hagon say the tight coil should be to the top when fitting their springs. If my old springs were in upside down, would you expect this to actually be the reason why my forks bottom out on the brake just wheeling it around the garage, or are the springs the wrong ones and too short or missing a spacer.
Looking for some info before I call Hagon when they open after the break.
Many thanks

[sonic]

Just checked Heiden Tuning & their pro springs are 484mm long, same length as the ones I just took out.
Just measured length of my preloaded adj fork caps which are 57mm long, how does this compare with non adj fork cap length.

[grizld1]

Sonic, the Hagon springs might work with older nonadjustable fork caps, but with the adjustable caps you'd be applying more than 40 mm. of preload with the adjusters at minimum setting. Those are definitely longer than OEM springs for your E-model forks, which the Yamaha factory manual lists at 482 mm.

Orientation of the spring (tight coils up or down) isn't a significant factor in its performance. Progressive Suspension and Yamaha recommend installing tight coils down; the claim is that this orientation reduces spring noise. Your old springs came out in the original orientation, and reversing them wouldn't have caused an unladen suspension to bottom in any case. I don't know where the problem lies, but you may want to have a good look at the factory service and parts manuals at www.biker.net . You'll find information on the coil OD and wire diameter for the OEM springs; a previous owner may have swapped in springs with correct free length and incorrect rate. Your fork assembly doesn't use spacers on the springs, only slugs between the springs and the caps.

[5twins]

Make sure your caps are set to their lowest position. Each step up adds about 10mm to the preload and length. Easiest way to install top caps is with a T handle because you can push down and turn at the same time .....



The plain plug caps as used on the '77 model add about an additional 22mm when screwed in. Your adjustable cap will add 33, 43, or 53mm depending what position you have it in. The '77 plain cap will fit in your fork. You may want to contact Hagon about the recommended cap. Some spring makers specify using the plain plug type with their springs. The factory shop manual specifies tight wound coils up.

[sonic]

These old bikes eh, I'm always on a learning curve, which is always good.
Much appreciate the info.
I'll give Hagon a call on Tuesday as the springs seem too long, possibly even with flat caps. Maybe they sent the wrong ones, let's see.

[650leo]

Your stock springs are wound from 4 mm wire, with an outside diameter of 24.5 mm.

[sonic]

Spoke to the nice people at Hagon and they say they've sent the right length springs, 520mm and not had any problems so far with previous orders. They only sell this length for the XS. They'll do a refund if required so no problem but it leaves me with another question.
My xs650 is a UK model but now wonder if sometime in it's past it's had a set of US forks fitted. According to the Heiden site, forks with the pre-load adjuster were not available outside of north america. I think Hagon said they've not heard of xs650 forks with preload adjusters. You'll see in the photo that I'm never going to get the fork cap onto the tube thread, it's got about 60mm to travel. The Heiden flat fork caps look like they might work but that'll be more expense.
Any UK bike owners have preload adjusters as well?

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[5twins]

You can probably force them down in using, like I said, a T handled wrench. Of course, with that much pre-load, the forks may end up being too stiff for you. The plain caps may be your only option in that case.

[650leo]

With the flat caps the preload can be adjusted by using different length tubing bewtween the cap and spring. I doubt you will need any with that long a spring.

[sonic]

Thanks,
I think I'll go for the plain caps which will mean only about 20-30mm of fork compression once tightened up. As it might give better action with the longer Hagon springs.

Can I just clarify, do the fork springs handle the rate the forks compress and then the weight of the fork oil deals with the damping (rebound). Because with the current (old) 485mm progressive springs the forks dive almost the full travel on the brake wheeling it around the garage, this gets a lot worse when riding. Looking at the springs, they have not "taken permanent set" (changed shape) as the Haynes Manual refers to so replacing them with another pair of 485mm fork springs would seem possibly a waste of time, unless springs degrade in some other way? Or they have the wrong rate as grizld1 mentions.

Dug out my Haynes and found the following (for 1977 to 1983): spring free length for UK XS650 & US XS650D is 470.5mm.
Spring free length for UK XS650SE, US XS650E/F/G/H/SE/SF/2F/SG/SH/SJ/SK is 482mm
It also says that UK XS650SE models had the preload adjusters, and a 1979 Yamaha Model Guide/Service Manual in English/French/German says the standard XS650 has fork spring preload adjusters. Confused? I am!

[grizld1]

Sonic, the spring rate controls how far the forks travel under a given amount of pressure. Damping is a matter of how quickly the forks respond on both compression and rebound; that's handled by oil viscosity selection and the valving in the damper rods.

It doesn't sound like you're confused at all, but the good people at Hagon are either confused or less than candid: "Sold thousands, never had a problem"--where have we heard that one before?

[5twins]

When you reassemble, use a bit more oil than the spec. This will help with the nose diving and these forks just plain work better with more oil. The stock spec is just under 6 ounces per leg, I run about 7.

[sonic]

Some good news that might be of interest for others.

Mulling it over, it just didn't make sense to lay out more money on a set of flat caps for those long springs and then end up with a set of springs with no pre-load adjustablility, I'd end up with less!
I spoke again with Hagon and asked what they had in a 485mm length. They had a set which compare as follows with the XS Hagon spec;
Hagon XS650: 24.7 diameter x 520mm: rate is 4.40 to 6.00
Hagon alternative: 25.0 diameter x 485mm: rate is 5.50 to 8.30
The Hagon alternative spring fits a wide range of bikes, Honda GL500, CB550. CB750, XL250! Suzuki GS550E, GSX750, Cagiva 650 allazurra, and now, I'd say it fits the XS650 very well.

Because the old forks dived like a premiership footballer I took a gamble that the extra spring rate on the alternatives would be ok and did the swap, atleast they're the same length, albeit a slightly larger diameter.
I've used 15w fork oil which I filled to 6.5 inches below the top of the compressed fork tube (around about 8oz in each leg). I know 6 inches is recommended but I thought putting a bit less in may compensate for the stiffer/wider springs.
Now the good bit..... the test ride. Just got back from a local ride and it's a massive improvement, it feels like a modern bike. What I mean is that I'm not aware of the suspension, whereas on the old springs I'd be diving everywhere boinging and riding accordingly looking out for the bumps to avoid and especially trying to avoid heavy braking. Now it just gets on with it, fantastic.
It's on it's slackest pre-load setting and I've also dropped the tubes through the yokes by 7mm. This I think gives me a reduced amount of suspension travel between the top of fork tube plastic cap to the bottom yoke, which is 114mm. I zip tied the fork leg before I went out and the most it's travelled today is 88mm. I hit a bunch of speed humps hard at 30mph on the ride and some heavy braking, overall I'm very chuffed as it's a massive improvement to the ride.
For info, the Hagon part number for the progressive springs is 400-083-00.
Once again, many thanks for all your input which is invaluable.