Triumphrat

champ87 · 12-10-2010, 02:24 PM

This post describes the work I did to upgrade the suspension on my ‘06 Sprint ST. I hope my photos and description will help others who want to maintain or upgrade or simply enlighten those who are curious about what’s inside their forks. This information does not apply to pre-’05 Sprints that use old-style damping rod forks. For more photos check my album.

There are several alternatives available for upgrading Sprint suspension. I’ll review the various options in a separate post and focus on the maintenance tasks in this post. To upgrade my forks I used new straight rate springs and revised the damping by replacing the compression and rebound valves with Race Tech Gold Valves. I also replaced the bushings (Teflon-coated bearings) and seals. While the forks were removed I took the opportunity to inspect, clean and lube the steering head bearings too.

Rebuilding Sprint forks is not difficult but does require more than just basic levels of skill and experience. I would recommend having a manual to hand. For coverage of suspension maintenance I consider the Haynes manual superior to the factory manual. I’ve broken the description into sections so even if you’re not doing a full rebuild there should be enough information to help with each of the following operations:

Fork oil change
Replace springs
Upgrade with Race Tech Gold Valves
Install new bushings and seals

Tools required

For fork overhaul your selection of tools should include the following:

24mm wrench or socket for fork caps.
Leak-free tray for collecting/cleaning parts.
Torque wrench.
Bushing/seal driver (or suitably-sized piece of pipe).
Fork oil level tool.

Tools required for installing Race Tech Gold Valves are listed in the instructions for the valves.

Replacement Parts

Fork Dust Seals - Triumph Part # T2046234 (if replacing)
Fork Oil Seals - Triumph Part # T2046232 (if replacing)
Fork Bushings, Outer - Triumph Part # T2042889 (if replacing)
Fork Bushings, Inner - Triumph Part listing not available (if replacing)
Sealing Washer for Damping Cylinder Bolt - Triumph Part # T2042907 (optional)
Fork Cap O-Rings - Triumph Part # T2042905 (optional)
Preload Adjuster O-Rings - Triumph Part # T2042933 (optional)
Fork Springs (for upgrade)
Race Tech Gold Valves (for upgrade)

Consumables

Plenty of Paper Towels
Kerosene (Paraffin) or Cleaning Solvent
Suspension Fluid
Grease for Seals (if dismantling forks)
Loctite 271 – Red
Plastic Bag or PVC Electrical Tape to put over end of fork tube to protect seals (if dismantling forks)

1 - Remove Forks

All of the tasks described were performed with the forks removed. The forks can be removed with the fairing in place but removal is a good precaution to reduce the chance of damage.
Before removing the forks I loosened the fork caps. The fork caps mark very easily, as I discovered on a previous occasion, so I wrapped some masking tape around the hex before using a socket.
In the base of the fork leg there is a bolt that holds the damper cartridge in place. It doesn’t need to be touched for oil change or spring replacement but I planned to completely dismantle the forks. To make it easier to remove later I loosened the damper cylinder bolt slightly while the fork was still held in place.
After loosening the bolts on the bottom triple clamp, top triple clamp and handlebar the fork leg pulled out with a little bit of twisting.

2 - Remove Spring and Drain Oil

With one fork on the bench I unscrewed the fork cap. There is some spring preload tension but minimal force pushing on the cap when it’s released.
The cap is held on the damping rod by a locknut screwed against the preload adjuster. To loosen the locknut I screwed in the preload adjuster to expose the flats on the threaded end of the adjuster. With a pair of 14mm wrenches I undid the locknut & removed the fork cap/pre-load adjuster from the damping rod.
The spring is held in place by a cupped washer. A slot in the washer allows it to be removed from the damping rod. I lifted out the spring slowly to allow oil to drain from it.
I poured the oil out of the fork tube into a container, pumping the damping rod a few times to help oil flow out of the cartridge. I inspected the oil for any debris that could indicate excess wear and/or damage that should be investigated during strip down of the forks and damping cartridge.
The following sections describe work to the damper cartridge and replacement of bushings and seals. If the aim is to simply change fork oil or replace springs then skip these tasks and jump to Section 8.

3 - Remove Damper Cartridge

My next step was to remove the damper cartridge. I removed the bolt, loosened earlier, from the bottom of the fork leg and lifted the cartridge from the fork. The bolt came out easily without the need for a cartridge holding tool.
It is recommended that the cartridge and valves are stripped and cleaned. If you are not comfortable with that and simply want to replace bushings and seals then make sure the cartridge is cleaned thoroughly before moving on to fork dismantle in Section 5.

Damper cartridge removed from fork tube.

Contd…..

champ87 · 12-10-2010, 03:04 PM

4 - Disassembly/Reassembly of Damper Cartridge

Sprint forks are 43mm Showa Conventional Cartridge type. In cartridge type forks damping oil flow is controlled by valves and shims. I replaced the stock Showa compression and rebound valves with Race Tech Gold Valves custom configured to provide improved damping. Race Tech provides comprehensive instructions and a video to cover installation of Gold Valves so there’s no need for me to repeat it in full. However, the same procedure applies to the stock Showa components so I’ll provide details of what I did.

There is a cone-shaped oil lock piece that fits on the end of the cartridge. I pulled that off to expose the compression valve assembly located in the bottom of the cartridge.
There is a small wire retaining clip that holds the compression valve in the bottom of the cartridge. I removed the clip and the valve assembly simply dropped out. If it’s a tight fit the holding bolt can be screwed into the valve body to pull it out.

Stock Showa Rebound and Compression Valve assemblies.
The compression valve components are held in place on the aluminum valve body with an allen bolt. Holding the valve body in soft vice jaws I removed that bolt and collected the components on a piece of wire to keep them in order. I did that mainly for reference – I would be replacing those items with new Race Tech components.

Stock Showa Compression Valve components. OK, the $ bill isn’t part of the valve it’s there to provide scale!
If the original Showa components are going to be reinstalled then a useful tip is to clean the faces of the pistons. This is done with fine wet & dry paper on a flat surface (piece of glass) and only requires a few strokes to achieve a flat finish.
To use Gold Valves in the Sprint forks it is necessary to drill a bleed hole in each valve. Race Tech recommends a standard bleed hole size of 1.3mm (#55 drill bit) for street use. For racing a smaller bleed hole size of 1.0mm (#60 drill bit) is recommended to provide stiffer low speed damping.
To ensure proper assembly I selected and laid out the compression valve components in the correct order. The components can be considered as groups – there’s the compression stack, the restrictor valving, the valve itself and the check valve.
The restrictor valve adjusts the size of the compression port and the amount of preload on the valving stack. Preload creates a digressive damping curve that provides firm damping at low speed without becoming harsh at high speed. The valving stack is the collection of shims that control the damping. To determine the number and size shims I used Race Tech’s online Digital Valving System. I simply input spring rate and rider preferences and it produced a spec sheet with a custom valving selection to achieve the desired damping characteristics.

Compression Valve components - Stock Showa vs Race Tech Gold Valve.
With all the required pieces laid out in the correct order I assembled the valve. There is a critical check to ensure the spring cup sits properly on the compression shaft. This is clearly highlighted on the instruction sheet.

Rebuilt Compression Valve with Race Tech Gold Valve. The check valve must move freely on the shaft
With the spring cup correctly seated I applied a drop of Red Loctite and installed the bolt. For Race Tech Gold Valves the supplied brass bolt must be torqued to ”no more than” 30 lbf-in (3 Nm).
The compression valve was now ready for re-installation so I moved on to the rebound valve which is assembled on the end of the damping rod. The locknut for the preload adjuster was still in place on the other end of the damping rod. I removed that nut to withdraw the damping rod from the cartridge.
The rebound components are held in place by a nut on the end of the damping rod. The end of the shaft is peened so I had to file it to remove that nut (Loctite was used for re-assembly). As before, I collected the nut and other components on a piece of wire to keep them in order.
There were a few steps to prepare for reassembly. The first was to polish the damping rod to ensure it moves freely through the bushing in the damper cartridge. Fine wet & dry paper (#1000) is suitable. I used steel wool.
The top out spring on the outside of the damper cartridge should be inspected for any signs of damage or failure.
Just as I had done with the compression valve I drilled a bleed hole in the rebound valve.
I laid out all the components in the correct order and assembled them on the damping rod. I installed the nut with a drop of Red Loctite and torqued it to 30 lbf-in (3 Nm).
I applied some fork oil to the (nicely polished) damping rod and slid it back through the bushing into the cartridge. A generous dab of grease to the threads of the rebound rod will prevent damage when pushing the rod back through the bushing at the head of the damper cartridge. A sealing “piston ring” is fitted on the outside of the rebound valve. A small dab of grease held the piston ring in place while I inserted the rebound valve back into the cartridge. I moved the damping rod up and down a few times to check for smooth operation then refitted the locknut on the other end of the damping rod.
To install the compression valve I first fitted the O-ring, with a small amount of fork oil to assist. I put the valve assembly back in the cartridge and fitted the small retaining clip.
I refitted the cone-shaped oil lock piece on the end of the cartridge to complete the cartridge assembly.
If the seals or bushings are not being replaced the cartridge can be re-installed without further disassembly of the forks. In that case skip the next section and jump to Section 6.

Contd…..

champ87 · 12-10-2010, 03:05 PM

5 - Replace Seals and Bushings

I replaced the bushings and seals to make sure I get the best performance from my suspension upgrades. It may not be necessary to replace bushings if they are fairly new and in good condition. Seals should be replaced as a matter of course when the forks are dismantled.

I moved my attention back to the fork leg/tube. The first step was to remove the plastic stone guard from the fork leg. Then I removed the dust seal by prying it out of the top end of the fork leg.
I removed the circlip that was under the dust seal. The dust seal was discarded but the circlip was needed for reassembly.
The fork tube was still held in place in the fork leg by the seal. To separate the fork leg and tube I gripped and pulled them out several times in a slide-hammer action. The oil seal was drawn out with the outer bush and a washer that sits between them.
I removed the inner bushing from the bottom end of the fork tube. Although I was going to replace them anyway I inspected both the inner and outer bushing for excessive wear that could be a sign of damage or fork problems.
I inspected the fork tube for nicks, cracks or areas of excessive rubbing. Although nicks appear as depressions they have a raised “crater rim” that will quickly damage the seal lips. The nick should be rubbed down with fine grit wet & dry sandpaper. If you know or suspect that your bike has ever been dropped check the fork tube for runout. The simplest way to do that is to roll it on a piece of glass.
I inspected the inside of the fork leg for signs of damage or wear. An inspection mirror was required to get a good look at the bearing surfaces inside the fork leg.
After a final check to make sure the fork leg and tube were clean I was ready to begin re-assembly starting with installation of the new bushings and seals.
The first piece I fitted was the inner bushing. That was easily fitted by pulling the ends open slightly and snapping it into place on the lower end of the fork tube. I applied some fork oil to the bushing then put the fork tube back into the fork leg.
I applied some fork oil to the bearing (inside) surface of the outer bushing. Taking care not to scratch the Teflon coating, I slid the bushing over the fork tube along with the separating washer that goes between the bushing and seal. I placed the bushing by hand then tapped it into final position with the driver.
Before fitting the seals I placed a thick plastic bag over the end of the fork tube to prevent damage to the seal lips by the ends of the tube. The oil seal was first. I applied some seal grease then placed the seal on the fork tube and tapped it into place with a driver.
The retaining clip was refitted. After checking that it was correctly seated in its groove I fitted the new dust seal.

Contd…..

champ87 · 12-10-2010, 03:10 PM

6 - Install Damper Cartridge

I gave the damper cartridge a final inspection to make sure everything was spotlessly clean then lowered the cartridge into the fork tube. The bolt that fits through the bottom of the fork leg was refitted to hold the damper cartridge in place. A new sealing washer was used and the holding bolt tightened to the specified torque of 24 Nm. Those sealing washers can be re-used without problem but they are so cheap I replaced them just to be sure.

7 - Spring Preload Spacer

With new springs it was necessary to measure and cut the spring spacer to the required length. The aim was to achieve minimum preload of 15mm. To avoid mistakes I decided to use a piece of plastic pipe to make a trial spacer before cutting the aluminum spacer provided with the springs.
Sprint damper cartridges have an external top out spring. For this type the recommended method is to place the spring inside the fork tube and take a direct measurement. I put a washer, the spring, another washer and my temporary spacer into the fork tube. I extended the fork then placed a mark on the spacer to correspond with the top edge of the fork tube. From this I needed to deduct the fork cap height. With the preload adjuster backed out I measured from the top lip to the point where the spring touches the underside of the original cupped washer. I added 15mm to give the required minimum preload.
With my dimension confirmed I cut my temporary spacer and placed the parts onto the damping rod in order. With the fork extended I checked that I would have the recommended 15mm preload once the fork cap was screwed in place.
Using my temporary spacer as a template I cut the permanent aluminum spacer to the correct length. In my case a spacer length of 85mm was required to give 15mm preload with the preload adjuster backed out.

8 - Refill Fork Oil (Suspension Fluid)
For standard springs the oil level is set at 120mm from the top of the fork tube with the spring removed and fork fully compressed. That requires approx. 469 cc of oil per leg. The factory manual lists Showa SS8, classified as a 10W oil. I previously used Bel-Ray 10W Fork Oil that seemed to provide the same damping as the original.
For my setup with Race Tech Gold Valves I used RaceTech Ultra Slick US 1 suspension fluid as recommended and supplied by them (well what else are they going to recommend?) RaceTech US 1 is labeled as 2.5 – 5 wt, a much lower viscosity than standard.

With the spring removed I filled the fork with oil. To distribute the oil I held my hand over the fork tube opening and compressed the fork. The pressure in the upper chamber helps oil flow through the cartridge. Bleeding was completed by lifting the damper rod a few times to make sure there were no air pockets in the cartridge. Oil level can measured with a simple dipstick or adjusted with a proper tool. I used a Mityvac vacuum pump configured to measure the correct level and draw out excess oil. I set my oil at the level recommended by Race Tech as part of the Digital Valving Search used earlier to for shim stack configuration and settings.
Standard springs are placed with the close wound coils at bottom. I fitted my new spring with a washer at each end then the spacer. Using hand pressure to compress the spring slightly I slipped the original cupped washer onto the damping rod under the locknut.
The locknut must be set to 10.5mm from the top of the damper rod - the height specified in the manual. With the correct height set I screwed the fork cap down and tightened the preload adjuster against the locknut.
Before installing the fork cap I fitted new O-rings to the cap and preload adjuster. This is optional but I’d already bought new seals just in case the old ones weren’t in satisfactory condition. The fork cap is tightened to a torque setting of 25Nm.
I refitted the plastic stone guard to the fork leg and repeated the whole operation for the other fork.
When refitting the fork legs I tightened the bolts for the bottom clamp only. I refitted the wheel and axle but before tightening the remaining bolts I pushed down on the front suspension a few times to allow everything to align. To help the triple clamps align I loosened the headstock nut slightly. After bouncing the forks, I retightened it to the specified torque then the bolts on the top triple-clamp and the two axle clamp bolts.

9 - Setting up Suspension

With everything re-assembled I set preload to give correct sag. This link provides information on how to set sag so there’s no need for me to repeat it here. If you regularly ride with luggage or a passenger it’s a good idea to also check static sag in that configuration. Make a note of the settings so adjustment can be made quickly when needed.
With these changes I will need to check headlight adjustment. Read this article for more information. In theory there should be no change if static sag is set to the same level it was previously but it would make sense to check.

Riding Impressions

Unfortunately cold weather has got in the way of any objective assessment of how the bike performs with these upgrades. I will post my thoughts later once I've had a chance to properly evaluate the changes.

More Information

Race Tech’s Motorcycle Suspension Bible is a superb resource for anyone who wants to know more about motorcycle suspension. It’s not Sprint specific but there is so much useful information in there that will be useful to novices and experienced alike.

KevyKev · 12-10-2010, 04:54 PM

Wow. Fantastic write-up Champ!! Thank you VERY much.

Tmod · 12-10-2010, 06:09 PM

Thanks for taking the time to put together such a nice tutorial, Job well done.

Tmod

oldndumb · 12-15-2010, 01:04 PM

Beeyoutifully done!

But then, that is what we have come to expect of your posts.

Stravoxylo · 12-15-2010, 03:01 PM

WOW. Excellent write up. Well done and very timely for me, as I plan to tackle this project in the near future.

Your effort is very much appreciated.

DaveM · 12-15-2010, 03:13 PM

Thank you very much champ87 for such a well thought out and comprehensive thread on how to do this.

Great photos too.

Thank you and well done

cheers
DaveM

Onedwn5up · 01-10-2011, 09:00 PM

Great write up. Serves well to remind people what they are paying for when they send their stuff out to a suspension shop or specialist to have their stuff worked on. Its a very detailed process and requires great attention to detail, other wise your forks can lock up on you and that is very unpleasant.