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Guide to: Replacing Fork Oil [message #215344] Thu, 17 June 2010 13:23 Go to next message
Kermit is currently offline  Kermit   United Kingdom
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(22) Giacomo Agostini
Kerms Guide to: Fork Oil Replacement

Replacing fork oil is often overlooked when it comes to routine maintenance but for little more than 2 hours work and £10-12 for the oil, it can transform a tired front end so its worth having a go.

I'd recommend fork oil is replaced at least every 2 years or 8000-10000 miles. This guide covers a CBR929's forks, but most bikes with USD forks are very similar. If your bike has right-way up forks then its even easier as aside from getting the forks out, its more or less just a case of unscrewing the top cap, removing the spacer and spring then draining the old oil and refilling with the same quantity of fresh oil although its probably best to also do the oil level measurement to double check the quantity added is correct.

Tools Required
1. Abba stand or a front stand that lifts from the underside of the lower yoke (or some inspired hoist mechanisum)
2. Socket Set (mainly 10mm, 12mm, 13mm, 14mm and whatever size bolt holds your front axel on which is normaly 20-24mm)
3. Adjustable Wrench (for top bolt) unless you have a huge 20mm+ spanner that fits
4. New Fork Oil of the correct weight and quantity for both legs

A trusty old Abba stand comes in useful
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_68.jpg

Front Mudguard off and main axle & calliper bolts removed/loosened
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_69.jpg

Front of the bike lifts up quite easy with a small jack. There's not much weight on the front as the abba pivots close to the centre of gravity
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_70.jpg

Front Wheel Out, fork top caps are best loosened a little while still clamped then remove the fork legs
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_71.jpg

Forks out
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_72.jpg

After removal of a small circlip, the preload adjuster is the first bit to remove............
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_73.jpg

....followed by this tripod thing that can be hooked out with a piece of wire
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_74.jpg

Unscrew Top Cap, press down on the spacer/spring to expose the 17mm Damper rod, then counter hold the top bolt and undo
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_75.jpg

After the top cap is off, remove the washer, slim spacer and main spacer
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_76.jpg

The spring is slightly slimmer at the top end
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_77.jpg

[Updated on: Fri, 18 March 2011 20:01]

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Re: Guide to: Replacing Fork Oil [message #215346 is a reply to message #215344] Thu, 17 June 2010 13:26 Go to previous messageGo to next message
Kermit is currently offline  Kermit   United Kingdom
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(22) Giacomo Agostini
cont...

Draining Oil (pump damper rod and fork leg to help speed the process)
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_78.jpg

I got 400ml of oil out of each leg (so far) which is a good bit below the 488ml oem level mentioned in my manual but my forks have had the K-Tech treatment so that might be reflected in the oil quality they beleive is correct for fettled forks.

The oil below despite the picture making it look almost black looked quite good with still a hint of gold colour and didn't contain traces of metal particles like I've seen on other bikes I've changed the fork oil on. It could be the original Motul Factory line (like the new stuff to the right) stays in grade longer and doesn't blacken as much as mineral based fork oils as its slippier nature than mineral oils [a similar way to synthetic (or semi) oils in engines] reduces wear. So might be worth paying the extra £5 or so for synthetic fork oil but thats just a gut feeling

http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_79.jpg

Fork Bits
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_80.jpg

Fork Legs Draining for hours/overnight to see how much more oil comes out
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_81.jpg

Hi-Tech fork oil level tester

I've gone with oem amount of oil as the forks felt under-damped which is partly why I'm doing this job. I put approx 420ml in each leg then measured oil level. The CBR929 is supposed to have 90mm gap between the oil and the top of tube when the tube is s compressed and without the spring so thats what I went with. For other bikes check the manual.

You have to pump the damper rod at least 10 times to make sure the dampers cavities take up their fair share of oil prior to the oil level measurement. Its quite interesting playing with the compression and rebound damping adjusters in between compressing and pulling the damper out to get a feel of what the damping each way is like without the spring tension smile
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_82.jpg

You can just about see the oil level
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_83.jpg

Spring in, spacers on and top cap on then tightened to some sort of torque that felt about right
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_84.jpg

Tripod thing already popped back in, then preload adjuster back on
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_85.jpg

Job done
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/CBR929_86.jpg

Took approx 1 hour to the point of being ready for fresh oil, then another hour to fill, get forks back together and refit to the bike.

[Updated on: Tue, 19 April 2011 21:22]

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Re: Guide to: Replacing Fork Oil [message #215977 is a reply to message #215346] Thu, 24 June 2010 18:40 Go to previous messageGo to next message
SPAL is currently offline  SPAL   United Kingdom
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Hi Kermit,

see u used 5w fork oil, is that whats recommended for 929's or is it to "soften" them up.

893 uses 10w as standard, don't know what difference changing from 5-10-15-20 would make?

Very oftem your told it will "soften" or "harden" but without experience in this area its hard to gauge.

Would think its less than changing springs though, or (as he types) he thinks surely oil & springs do different though connected jobs in a fork.

SPal
Re: Guide to: Replacing Fork Oil [message #215983 is a reply to message #215977] Thu, 24 June 2010 19:17 Go to previous messageGo to next message
andy_scouser is currently offline  andy_scouser   United Kingdom
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(16) Barry Sheene
We need this on YouTube smile

you really are very adept at all of this aren't you Kermit. Well done mate
Re: Guide to: Replacing Fork Oil [message #215986 is a reply to message #215977] Thu, 24 June 2010 19:49 Go to previous messageGo to next message
Kermit is currently offline  Kermit   United Kingdom
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(22) Giacomo Agostini
SPAL wrote on Thu, 24 June 2010 18:40
Hi Kermit,

see u used 5w fork oil, is that whats recommended for 929's or is it to "soften" them up.

According to my 929 manual the recommended oil is Pro Honda Suspension Fluid SS8 which I guess is a an 8 weight oil. I went with 5w as I have the invoice from when my forks were fettled by k-tech for one of the previous owners and its shows they filled it with 5w oil of the same type brand and type that I bought on ebay although I went with oem fluid levels while I suspect k-tech went with less as I needed about 40ml more in each leg than i drained to get it to the correct level.

Quote:
893 uses 10w as standard, don't know what difference changing from 5-10-15-20 would make?

I wish i could help but my understanding of it is all a bit vague although I suspect just a change from old 10w [which I guess degenerates to something maybe closer to 5w oil over time] to fresh 10w oil would help restore damping.

I'd guess that going up a weight in oil in effect makes the damping action in both directions firmer/slower where as a lower weight reduces the damping but I suspect thats a very simplistic view of things and I'm just thinking from the pov of the physics of squeezing oil through the damping passages as I imagine thicker oil will need more force to send lets say 150ml through a 4mm hole in a given time than a thinner oil and visa versa.

This does make me think that part of the purpose of k-tech and the like fitting alternative compression or rebound damping (or adjusting the standard openings) is if you simply rely on thicker or thinner oil to achieve more or less damping, its works equally on both comp. and rebound where as you might just want the effect on one or the other (if that makes sense Confused)

andy_scouser wrote on Thu, 24 June 2010 19:17
We need this on YouTube smile

you really are very adept at all of this aren't you Kermit. Well done mate

Thing is I didn't video any of it like i did with the exhaust so possibly not a very interesting video. What I need is someone to video me while I do it with bleeps in the appropriate places Laugh

Thanks smile

[Updated on: Thu, 24 June 2010 19:54]

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Re: Guide to: Replacing Fork Oil [message #215991 is a reply to message #215986] Thu, 24 June 2010 20:07 Go to previous messageGo to next message
andy_scouser is currently offline  andy_scouser   United Kingdom
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(16) Barry Sheene
When I first got the gixxer, i was too brutal with the throttle and id get head shake. The std damper has 10w oil in it and is non adjustable so a cheap mod was to undo a screw and push all the oil out. Once empty, immerse the damper in 15w oil and pump the damper till no air bubbles came out, then put screw back in, all under oil level. This would give a much stronger dampening effect, so ... id assume the same applies to suspension as its basically does the same job.
Re: Guide to: Replacing Fork Oil [message #216010 is a reply to message #215991] Thu, 24 June 2010 21:07 Go to previous messageGo to next message
SPAL is currently offline  SPAL   United Kingdom
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(13) MotoGP Champion
Yeah,

All sounds very clever and I guess the only real way would be to experiment with different oil in the same fork without changing any other variables.

That way you would be sure what effect the oil viscosity has, not in therory, cause obviously a thicker oil pushed through the same size hole, as kermit says, should stiffen the fork up, but by how much?

Oh the wonders of the universe.

Now to ponder something simpler (world peace) Laugh

SPal
Re: Guide to: Replacing Fork Oil [message #216142 is a reply to message #216010] Sat, 26 June 2010 10:26 Go to previous messageGo to next message
the beer hunter is currently offline  the beer hunter   United Kingdom
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(17) Kevin Schwantz
Cheers for this Si.
Been meaning to do mine, in fact I should be collecting a 2007 set of forks today (eBay £90) for the DRZ. smile
Wouldn't mind checking the bushes & replacing seals too but I've never done anything like that before.

Been reading up on mine & the stip-down looks similar but with a pushrod, needle & spring that falls loose. The bleeding process looks like an art too. smile

Thumbs Up
Re: Guide to: Replacing Fork Oil [message #216179 is a reply to message #216142] Sat, 26 June 2010 21:13 Go to previous messageGo to next message
the beer hunter is currently offline  the beer hunter   United Kingdom
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(17) Kevin Schwantz
I was concidering using these guys (Brook suspension) 'cos for 100 notes they strip, check for wear, fit new seals, oil etc.
Only 55 miles from me.

I may give Kais a call as they're nearer & see how much they charge. Anyone had dealings with either company?




Re: Guide to: Replacing Fork Oil [message #216376 is a reply to message #215344] Mon, 28 June 2010 22:40 Go to previous messageGo to next message
Kermit is currently offline  Kermit   United Kingdom
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(22) Giacomo Agostini
Quazi wrote on Fri, 11 June 2010 20:32
That oil look bad enough Kermit, it won't end up like engine oil. smile

See, I told you it still had a hint of gold colour in it Grin

As I didn't have an empty container to put the old oil in, its sat in the tupperware for over a week has settled out to the point that I could almost reuse it Laugh
http://i498.photobucket.com/albums/rr345/KermitX/CBR929/SuspensionOil_1Week.jpg

Interesting?

[Updated on: Mon, 28 June 2010 22:41]

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Re: Guide to: Replacing Fork Oil [message #216377 is a reply to message #215344] Mon, 28 June 2010 22:44 Go to previous messageGo to next message
Quazi is currently offline  Quazi   United Kingdom
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(22) Giacomo Agostini
I used to use old engine oil to paint my fences with, the smell went after a couple of weeks. Laugh
Re: Guide to: Replacing Fork Oil [message #216380 is a reply to message #216377] Mon, 28 June 2010 22:47 Go to previous messageGo to next message
SPAL is currently offline  SPAL   United Kingdom
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(13) MotoGP Champion
Cheeper than creasote. Laugh

SPal
Re: Guide to: Replacing Fork Oil [message #217108 is a reply to message #215344] Tue, 06 July 2010 20:17 Go to previous message
DrMartin is currently offline  DrMartin   United Kingdom
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(18) Geoff Duke
This is what I put in my Blade forks when I changed to the Ohlins (+ 10% stiffer) springs.

http://i244.photobucket.com/albums/gg17/Panther_058/New1/Image021.jpg

I can't remember now where I got the advice about using 7.5 from (probably here) but it all seemed to work well.

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