Thruxton R Fork Oil Change

Details of previous work to change the suspension characteristics of my TTR can be found in the thread Thruxton R Suspension Modifications. I decided to write a separate thread here because the procedure for changing the fork oil on the Showa BPF (Big Piston Fork) is not effected by my mods. However, just to recap, I've fitted lower rate springs on the rear and Maxton fitted lower rate springs in the forks. Why? Cause I'm a lightweight and it was just too, dam hard for riding on country roads. But it's not just me by the way and here's what jouro' Dave Manning had to say in the recent MoreBikes publication whilst doing a side-by-side comparison of the new TTR with the RE Continental GT around the roads, I ride, in Lincolnshire. "......and while there's not the level of feedback from the tyres that I'd really like, you do feel every bump, ripple, pebble and groove in the road. Initially it feels like a late Seventies Ducati, or an early Nineties special, so hard is the suspension. It'd be an ideal track bike......but just a dozen miles on bumpy Lincolnshire byroads give your wrists a true hammering."
I've just got back from a 40 mile road ride and I'm just so happy, after my latest & final tweek, that I've persevered to achieve this great handling, comfortable to ride Thruxton R.
So this last fiddle I've completed was to change the fork oil to the lowest weight stuff available, 2.5. Front end set-up is now:- 1/2 turn of compression damping, 2 turns of rebound, 1 1/2 turns of pre-load. I run both tyres at 2.2 bar pressure.
Nothing I have done is a recommendation to someone else to be followed but may provide some direction if you wish to alter the characteristics of your suspension. (well that's what everyone seems to add these days, afraid the some numpty is going to stuff it up and cause pain and damage then lay the blame elsewhere. But c'mon, we're not doing anything groundbreaking here)
Right let's get this oil changed. If you're old school, skint or stupid you can dismantle the forks with home-made tools (the Haynes way) and mole-grips otherwise get on flea-bay or similar and buy a Fork Cap Removal Tool and Spring Support Remover for the Showa 43mm BPF. A Fork Oil Level Gauge is also worth while, although a knitting needle plus a ruler will do and are unlikely to cause damage to your expensive bouncy bits. As each fork requires just over 550 cc of oil, and it comes in 1000 cc containers, then two bottles of oil needed.
Forks must be removed as the only way to drain the oil is to turn them upside down. Therefore :-
1. Turn all adjusters to 0, noting number of turns and using an old towel to protect the tank, clocks and top yoke, loosen the fork top caps after positioning the bars to full left lock.
2. Bike raised up safely and squarely so that front wheel is just clear of the ground. Tip - start to slacken fork clamping screws. brake caliper bolts, wheel spindle clamping screws and wheel spindle while there is still weight on the front wheel and, where possible, position the handle of your wrench so that you're applying downward force. Note the position of the wheel spindle-end in relation to the hole chamfer on the offside (clamping side) fork leg. Photo 12.( Due to attachment limits I will add on subsequent post,)On re-assembly, it needs to be correctly positioned to ensure alignment of the corresponding brake caliper with the brake disc.
3. Remove the mudguard.
4. Remove the ABS sensor noting the washer shaped shim positioned under the screw head.
5. Remove the brake calipers from the forks, wrap them in cloth and cable tie them to the exhaust pipes. Tip - Do not touch the front brake lever whilst the calipers are removed from the discs. Place a label on the brake lever to remind yourself.
6. Remove the front wheel spindle noting the position of the hub spacers.
7. Remove one fork leg Tip - if the job is completed on one unit at a time no components an get interchanged by mistake.
8. Protect and clamp in bench vice - Photo 1
9. Remove top cap - Photo 2
10. Slowly push the upper fork tube down into the lower. Photo 3 - It is not necessary to dismantle the cap from the damper rod for an oil change.
11. Photo 4 - Spring Support requiring special Removal Tool
12. Remove Spring Support - Photo 5 & 6
13. Withdraw damper assembly allowing oil to drain into fork lower - Photo 7
14. Measure oil height - Photo 8 (I measured 134mm)
15. Invert the fork to allow all the oil to drain into a measuring jug. Tip - place a finger over the end of the tube to prevent the internal components from dropping into your oil container. If possible, clamp the fork inverted and leave it for 20mins to completely drain.
16. Photo 9 - the internal parts. Just wipe them clean/dry with a lint-free cloth and check for any damage also checking oil seals and O-ring in the top cap. Note: My forks have shorter than standard springs with a 20mm black, nylon spacer which can be seen in the photo. No spacer is fitted in the fork originally so don't panic - yours has not rolled under the bench.
17. Photo 10 (photo deleted due to attachment limits) - checking the volume of oil removed. I measured approximately 550cc. Haynes lists the oil volume as 582cc which I would take to be the correct fill volume for a completely dry assembly.
18. Photo 11 - My choice of new HRX 2.5W fork oil. Maxton had used 5W in the earlier re-build.
19. Clamp the fork as before ensuring it is straight and vertical so as to get accurate oil height measurement. Tip - use a spirit level in two axis resting on the fork tube top.
20. Replace the internal components in the fork lower. White lower collar, open end up; spring; grey upper colIar, large open end down.
21. Slowly pour in 550cc of new oil. Looking down inside the fork tube the top oil level should align with the holes in the tube.
22. Slowly raise the upper tube, approx. 240mm, whilst keeping the lower clamped, place a hand over the tube top and slowly push back down to the bottom. Some air will leak past your palm but as long as you create some pressure in the tube it will force air inside to be displaced by oil. Repeat 10 times.
23. Check the oil height - Photo 8. Add or remove oil as required (The dedicated measuring tool incorporates a tube & syringe which makes life easier here). I added a further 20cc approx to achieve the height of 134mm I originally measured.
24. Replace the damper assembly and threaded spring support and tighten using the dedicated tool .Photos 5 & 6. Some downward pressure is required to overcome spring force when engaging the thread. Ensure there are a couple of turns of engaged thread before releasing the downward pressure and take care not to cross threads. Unless you have another special adapter it isn't possible to use a torque wrench. I used the same spanner to replace as I did to remove and I set my right arm to give an equivalent degree of tightness - grade Bloody Tight.
25. Slowly raise the upper tube so that you can engage the thread of the top cap and, using the tool, screw down hand-tight. Photo 2. Final tightening can be completed when the forks, wheel etc., is all reassembled.
26. Having done both fork legs and reassembled onto the bike with all the bolts nipped up:-
Tighten Top Caps (Bars turned to full right lock)
One fork leg at a time - slacken clamping bolts and rotate/lift/lower the fork upper tube to adjust its position relative to the top yoke.
Tighten all bolts & screws to correct torque setting taking care to ensure the wheel spindle is correctly positioned - Photo 12.
Pump the front brake lever then check the front wheel spins freely.
Re-set damping and pre-load adjusters.

 

Wheel spindle positioning.

 

Cheers and I hope it gives others to have the confidence to complete the job. After all there are TTRs, like mine, that are approaching 5 years old so it’s realistically a maintenance task now. There are some good and not so good YouTube videos re. Showa forks but how can you be sure that they are the same as used on a Suzuki/Honda etc.

 

£5 each side

 

I have noticed I make a misleading comment re. ABS sensor shim. It is NOT fitted under the screw head, it goes between the sensor body and mounting lug. The shim is there to set the correct gap between the sensor tip and wheel mounted rotor. Sorry friends.