HOW TO Change the Fork Oil on a GSX1400 (All Years)
NOTE: This thread is also available to download as a PDF file from the Downloads (General) Section
From reading the manual, many owners think this quite complex and beyond their capabilities but really it’s very straight forward.
In reading through this article, any quantities of oil for oil/air gap referred to are for standard springs. If you have fitted after-market springs like linear or progressive, use the oil/air gap advised with those springs. Note also that if progressive/linear springs have been fitted, then typically the plastic spacers I refer to below will have been removed also.
1. Get bike setup on Paddock Stand and Headstock stand
2. Remove calipers, front wheel and mudguard
3. Loosen off the two top yoke pinch bolts
4. Loosen off the nut on top of each fork (do not remove!)
You now can work on each fork at a time - so repeat these instructions for each fork leg
5. Loosen the pinch bolts on the bottom yoke of the fork you wish to remove and put and old cushion / blanket, bit of foam rubber etc. underneath where the fork will (almost) touch the ground when removed
6. Wiggle and twist the fork stanchion and slide it out of the yokes. You'll find it gets very close to the floor (hence the cushion etc. above to stop scratching it or banging it on the ground)
OK, the fork stanchion is now out of the bike and we can start on disassembly
7. Holding the top of the stanchion, undo the top nut that you loosened at #4 above. Once it is undone lift it straight up gently. You will see attached to the large nut a rod with a small locking nut underneath. Undo this locking nut and unscrew the rod from the large top nut.
8. Gently pull the small rod out of the fork leg and place to one side
9. Now compress the fork stanchion into the fork lower and pull out the spring and other bits attached to it (there will be a large plastic spacer. Note the order of assembly and which way up the spring is as you remove them (there may be a tapered end on the spring which needs to go back the same upon re-assembly)
10. Now get a bowl and turn the fork leg upside down and leave for about 5-10 minutes for all the old oil to drain out.
Dis-assembly complete â€" time to re-assemble
11. Holding the fork leg upright, depress the stanchion inside the slider (it probably already is anyway) and fill the fork leg up with fresh fork oil until the level of the oil is 108mm from the top of the stanchion (you can measure this by getting a plastic straw and marking it appropriately, holding it down inside the fork leg from the top).
NOTE: If using after-market springs, use the recommended “weight†oil and set the oil/air gap as recommended by the supplier. For standard springs, use 5w fork oil and set the oil/air gap to 108mm
12. Now, keeping the fork leg upright, and holding the slider, pump the stanchion up and down a few times - this gets rid of air in the inner fork. You’ll know when its full as the air bubbles will stop. Once you have done this, leave the fork leg upright for about 5 mins or so for the oil to settle and then re-check the oil/air gap is 108mm from the top of the stanchion (with the stanchion compressed into the fork leg). Adjust as necessary.
13. Now the oil is in, pull the stanchion out from the slider, and re-insert the fork spring and plastic spacer
14. Now get hold of the rod (removed at #8). From the end of the rod set the gap to the top of the small locking nut to 11mm. Once set insert the rod into the stanchion and keep hold of the top.
15. Screw the large nut from the top of the fork onto the rod so it just locates on the top of the nut (which we set the gap of at #25). Nip this locking nut up on the rod.
16. Placing a pad on the floor, and keeping the stanchion upright, screw the top nut into the stanchion. The springs will push back a bit, so you need to be firm in doing this. Once the large nut is located, screw it down into the stanchion but don't tighten it up quite yet.
17. Now insert the re-assembled leg into the bottom yoke and wiggling it again, push it upwards through the top yoke, so the top of the fork stanchion is level with the top of the top yoke.
18. Torque up the 2 pinch bolts in the lower yoke
19. Torque up the big nut on top of the fork stanchion.
20. Torque up the pinch bolt in the top yoke.
Assembly of Fork Leg Complete! Now repeat steps 5 through 31 for the other fork leg. Note in total you will use about 1.2L of fork oil for both legs. The oil/air gap is a better way of adjusting fork oil, as it allows for any discrepancies in manufacture of the fork leg itself.
21. Once both legs are done, re-assemble the mudguard, front wheel and calipers - not forgetting to pump your front brake a couple of times once the calipers are refitted - and just double check that all bolts are correctly torqued
That's it - job done! For someone who hasn't done it before, job should take about an hour or so to do.
Fork oil:
• 5W Fork oil recommended with standard springs
• 10W Fork oil typically used with aftermarket progressive / linear springs
Oil/Air Gap:
• Standard springs: 108mm
• Hagon progressive: K2-K4: 150mm, K5-K8: 160mm
• Ohlins progessive: K5-K8: 140mm
Regarding fork oil viscosity, there is no standard classification like SAE. Every manufacturer uses their own! Many don't even use xW. When deciding on a different viscosity, you need to stay with the same brand or determine your current oil's cSt-values. The table at the end of this page is helpful for this. Sorry, I think this is an old site but it will give you an idea,
http://www.peterverdone.com/archive/lowspeed.htm (http://www.peterverdone.com/archive/lowspeed.htm) One thing worth noticing on this page are the viscosity indices.
If you are picky about the viscosity you want, you can mix your own. Here a table from Motorex to get the viscosity you want http://motorex.bg/wp-content/uploads/Motorex-Viscosity-Blend-Chart.pdf (http://motorex.bg/wp-content/uploads/Motorex-Viscosity-Blend-Chart.pdf) with their fork oils.
If the forks are black inside from manky old oil then hold the bolt in the bottom with a finger & pour an inch or so of petrol into the leg. Swirl it around like buggery & pour it out. Repeat till clean.
Then allow to dry before adding oil.
Hi all, can I just ask which oil manufacturer most of you guys use for their fork oil change?
Was thinking of using Motul ?
Regards: Geoff
Quote from: Geoff Price on Wednesday, 09 December 2020, 08:49 AM
Hi all, can I just ask which oil manufacturer most of you guys use for their fork oil change?
Was thinking of using Motul ?
Regards: Geoff
Doesn't really matter Geoff, your choice.
Given this was your first post, it would have been nice if you could have introduced yourself - thanks https://gsx1400owners.org/forum/index.php?board=20.0
So, as expected, I'm half way through changing the fork oil/seals on the old girl and I've hit a snag.
All going well until I removed the adjuster rod and drained the oil. The inner (chrome) tube did move freely as I was removing the adjuster rod.
I've removed both adjuster rods and inverted the forks to drain the oil but when I try to 'stroke' the inner tube into the outer tube, as per the manual photo below, to drain out all the oil, neither fork tube will slide in. They both seem to be stuck at the full extension position.
I was considering not going further as I don't have the appropriate extracting tool and just refreshing the oil I've emptied and not replacing the seals but I'm concerned that if I put it all back together the forks won't slide it's all been a massive wast of time.
I could take them to a shop but my goal was to 'learn on the job' and save some coin.
Any ideas why the inner fork isn't sliding into the outer? Have I created an air lock or turned/twisted something I shouldn't have?😩
Thump it on the floor, not too hard but a decent tap. It's probably over extended & the bushes are jammed against each other. You can find they stick fully compressed too & need a solid tug to move again.
Thanks for the reply Hooli👍
I've given them both a fair ol thud on the concrete floor with a thick piece of cardboard as a protective buffer but still no movement. I fear any harder and I will break something. They both have a few millimeter of movement but come to an abrupt stop against 'something' if all it can be as you say, they have become jammed, wouldn't there be no movement at all?
...I'll build up some courage and give them another wack.
Cheers.
...when I say they have a few millimeters of travel I actually mean about 1/2 to 1 mil.
Your theory does seem consistent as they did move when I removed the inner rod and placed them upside down to drain, then 20mins later after doing nothing else to them, they are both stuck.
...I need a stiff drink before I try bashing them any harder.
Make sure that the inner rod can turn relative to the bottom tube. they could be hydraulically locked or jammed up with the old seals and scrapers and sliders. If they are skewed, try to get them straight to the bottom tubes and tap them in using a block of wood. Mine were pretty stiff as well.
Otherwise try pulling them out, the bottom of the tube is just flat and they should come out fully.
The chroming on the staunchions is pretty good, just be careful not to distort the tube from round.
Also the inner damper valves and its valve ports were blocked with cruddy oil. I sprayed them with brake cleaner/ wd 40 / crc whatever to remove the rubbish.
Thanks for replying Eric, that inner rod (that holds the adjuster rod) rotates freely and looks straight.
Is it this you suggest I hit down into the tube?
Not comfortable with all this bashing! Lol I'll give it a few more goes then I may have to surrender to the bike shop.
If only there was a video somewhere showing where exactly and how hard to hit, would put my mind at rest.
I will record what I do and if it works there will be a reference for the next poor soul who has to raise a hammer to their loved one 🙈
So youve drained all the old oil out?
And you have undone the damper (the inner slim cylinders from the bottom of the staunchion?
The chromed outer (large dia tube) should then pull out of the lower leg if you have removed the old seals
Phill, wish i could help but cant. I like to do all my repairs but never been interested in forks. I just take mine to local bloke, cost is is good, pay him a few bucks and refit. Just my way.
So, as I've already bought the replacement seals I went ahead and stripped the forks down completely. The tubes are seperate now, the damper rod, springs, 'that screw at the bottom' etc are all out.
I tried to dry fit the tubes to test if they would move over each other, as per my last post, but they still did not and the manual about re-assembly is not clear...to me.
I'm going to sleep on it and have another go tomorrow. I'm not confident I'll be able to fasten 'that bottom screw' tight enough as I don't have that special tool that holds the rod in place.
...so, if it doesn't come to me magically in my sleep tonight I'll have to admit defeat and call a man.
Oh, well, I had a crack and learnt a lesson...don't mess with things I don't understand that require special tools!
Thank you very much to those who gave advice.