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Old 02-24-2008, 05:10 PM   #1
redlineK4
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Fork oil change

My bike has just hit 20k km and I think it's high time to change the fork oil. Here is the question: Do I need to sparete top cap from fork using spring compressor (and block plate) in order to change oil or is it just enough to loosen the cap and turn fork upside down and drain old oil? Seals are in good condition and I see no reason to change them.

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Old 02-24-2008, 05:12 PM   #2
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Re: Fork oil change

If youre going to go to the lengths of changing the oil, you might as well open the entire fork up, inspect the springs, retainers, etc.
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Old 02-24-2008, 10:24 PM   #3
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Re: Fork oil change

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Originally Posted by redlineK4 View Post
My bike has just hit 20k km and I think it's high time to change the fork oil. Here is the question: Do I need to sparete top cap from fork using spring compressor (and block plate) in order to change oil or is it just enough to loosen the cap and turn fork upside down and drain old oil? Seals are in good condition and I see no reason to change them.
i have never done it with an inverted fork but i here it can be a pain in the ass
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Old 02-25-2008, 01:19 AM   #4
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Re: Fork oil change

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i have never done it with an inverted fork but i here it can be a pain in the ass
I agree. Id never want to have to use spring compressors, especially if I didnt have prior experience with them.
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Old 02-25-2008, 01:34 AM   #5
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Re: Fork oil change

You can just remove the top caps and remove the compression needle adjusters , drain the fluid. Flush with clean fluid and fill with new fluid.
  1. measure how much fluid comes out of each fork leg.
  2. replace with good fluid of similar weight
  3. changing weight will need shims to be changed as well
  4. Redline , silkolene , or Belray HVI reccomended oils.
  5. 489mls of fluid is standard from memory. in each fork
easy done , I hang the bike so the forks are fully extended and then the top caps don't fly of with heaps of force. you can compress the forks to help drain the fluid as well. it will take a while to fully drain.
good luck
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Old 02-25-2008, 03:30 AM   #6
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Re: Fork oil change

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Originally Posted by surreal5150 View Post
You can just remove the top caps and remove the compression needle adjusters , drain the fluid. Flush with clean fluid and fill with new fluid.
  1. measure how much fluid comes out of each fork leg.
  2. replace with good fluid of similar weight
  3. changing weight will need shims to be changed as well
  4. Redline , silkolene , or Belray HVI reccomended oils.
  5. 489mls of fluid is standard from memory. in each fork
easy done , I hang the bike so the forks are fully extended and then the top caps don't fly of with heaps of force. you can compress the forks to help drain the fluid as well. it will take a while to fully drain.
good luck

That's what I wanted to hear. I want my front end to be a little stiffer so I'll probbably put 15W oil ( a lot of track days this season). Why shims need to be changed along with oil weight?
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Old 02-25-2008, 08:31 PM   #7
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Re: Fork oil change

Changing the weight of the oil means it will flow slower through the valves and also flex/open the shims more easily, essential making the forks slower and softer in simple terms.

when you say you want the forks stiffer, do you mean they are bottoming out ???

Heavier springs will only stiffen the forks !!!
0.85Kg forks as standard , you could try 0.90's or 0.95's depending on your weight.

What are your sag measurements and how much preload do you run ????

if you want a simple but , only scratching the surface fix , just add a little more oil , reduce the air gap/spring in the fork , effectively making the last 10-15mm of travel alot firmer.

you want forks to be quick not slow, I would stick with a 5w or 7.5w oil personally. 15w I think would ruin your range of adjustabiltiy also.
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Old 02-25-2008, 09:18 PM   #8
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Re: Fork oil change

Quote:
Originally Posted by surreal5150 View Post
Changing the weight of the oil means it will flow slower through the valves and also flex/open the shims more easily, essential making the forks slower and softer in simple terms.

when you say you want the forks stiffer, do you mean they are bottoming out ???

Heavier springs will only stiffen the forks !!!
0.85Kg forks as standard , you could try 0.90's or 0.95's depending on your weight.

What are your sag measurements and how much preload do you run ????

if you want a simple but , only scratching the surface fix , just add a little more oil , reduce the air gap/spring in the fork , effectively making the last 10-15mm of travel alot firmer.

you want forks to be quick not slow, I would stick with a 5w or 7.5w oil personally. 15w I think would ruin your range of adjustabiltiy also.
Redline, These are all questions that you need to answer before you do anything. Also, how much do you weigh? That could also having a bearing. You may underweigh or outweigh your springs.
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Old 02-26-2008, 12:54 AM   #9
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Re: Fork oil change

Most tuners recomend a 10wt for these forks. I had 7.5wt in mine, worked well.
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Old 02-26-2008, 04:22 AM   #10
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Re: Fork oil change

The standard oil in these forks is a showa ss-05 ( a 5w oil).

Yes alot of tuners reccomend 10w oil in these forks but with changes to the shim stack, to accomodate the different weight oil.

So I think you need to answer some of the questions for yourself before doing anything.

Just to add more confusion to the subject , a redline 5w will be different to an ohlins 5w oil and different to a silkolene 5w oil and so on.

To put it even more simply - not all 5w oils are the same viscosity, they actually very quite alot.
Also companies produce standard and racing fork oils of the same weights which vary greatly in there properties and Price !!

If you want the best oil to go in to just replace the old stuff.
Belray 5w HVI racing fork oil is the closest to the standard showa oil in there now but with much better properties and resistence to thinning from heat.
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Old 02-26-2008, 10:40 AM   #11
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Re: Fork oil change

Does that much heat really build up in the forks under normal loads? I can understand racing with the bike consistently being on angles.
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Old 02-26-2008, 10:57 AM   #12
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Re: Fork oil change

Quote:
Originally Posted by surreal5150 View Post
You can just remove the top caps and remove the compression needle adjusters , drain the fluid. Flush with clean fluid and fill with new fluid.
  1. measure how much fluid comes out of each fork leg.
  2. replace with good fluid of similar weight
  3. changing weight will need shims to be changed as well
  4. Redline , silkolene , or Belray HVI reccomended oils.
  5. 489mls of fluid is standard from memory. in each fork
easy done , I hang the bike so the forks are fully extended and then the top caps don't fly of with heaps of force. you can compress the forks to help drain the fluid as well. it will take a while to fully drain.
good luck
No offense, but this is not an effective way to change your fork fluid. If you want to do the job right, you have to at least remove the caps, springs, & spacers. When we do even a basic fork service, we also pull the cart. Not necessary, but makes the job alot easier, quicker, and more effective. Once you've pulled the spring & spacers, it's only one more bolt to pull.

If you just drain fluid out the bottom... the fluid in the cartridge... which is what really matters... doesn't get changed at all. You could let the forks drain for a month and the fluid in the cartridge would still be there. Unless you remove the spring, there's no way to stroke the damping rod, and without stroking the damping rod, there's no way to get the fluid out of the cart. If you don't completely flush & refill the cart, there's not really much point in changing the fork fluid at all.

If you attempt to compress the fork with the springs in place, the result is even worse, because what you'll do is introduce air into the cartridge. Air that you won't be able to bleed out with the springs in place. If your carts aren't thoroughly bled, the suspension action will be terrible.
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Old 02-26-2008, 11:22 AM   #13
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Re: Fork oil change

I would also recommend sizing your fork springs to your weight as the first step to upgrading your suspension. But I definitely would NOT bump up the oil level from stock, and would NOT go with heavier fork fluid.

The main problem with most production forks is that the oil level is too high to begin with. It allows the manufacturers to put in (relatively) soft fork springs, which most street riders find more comfy, while still maintaining some bottoming resistance. The problem with this approach is that the highly progressive nature of the air spring makes the bottom 1/4 of travel waaaay too harsh, while the lightly-sprung initial 3/4 of travel allows you to dive right down to it. So... you dive, then hit a 'wall'. The forks may not mechanically bottom w/ a high oil level, but the feel of them will be very close to the same. The result in either case is suspension that doesn't move. And when suspension doesn't move, it's not working.

I've yet to work a set of forks that, once properly sprung, didn't require the oil level to drop significantly from stock recommendations. We typically set anywhere from 120mm-140mm, depending on other variables.

As far as oil weight goes... going w/a heavier oil may make the bike 'feel' like it handles better, but only because you've bumped up the compression damping, giving the bike a more solid platform. Turn transitions feel great... until you hit a bump or need responsive traction when loaded up in a corner. Then the suspension can't react fast enough, causing you to lose traction, and in the weeds you go. Proper valving coupled w/ proper springs, proper oil weight, and proper oil level can provide both a solid platform during transition as well as the ability to soak up pavement irregularities. But just bumping up the oil weight w/o doing anything else will generally make the compression damping too harsh.

FYI - there are benefits to going with lighter fluid weights, assuming you valve accordingly. The most common weight most suspension tuners use is 5wt (which, as surreal accurately pointed out, can vary according to brand).

If you're up to getting your forks revalved & resprung, rock on! Oil weight & level will be dictated by who does the work and what method they use to achieve their goals. But I'd leave the oil weight stock if you don't revalve. And if I did anything with the oil level, it would be bring it down, & get springs to match your weight & riding style.

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Old 02-26-2008, 11:33 AM   #14
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Re: Fork oil change

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I would also recommend sizing your fork springs to your weight as the first step to upgrading your suspension.

Think I already said this
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Old 02-26-2008, 11:36 AM   #15
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Re: Fork oil change

i'm sorry if I didn't give you the credit you deserve, 1K. You most certainly did say the same thing, and it was excellent advice. That's why I said "I would also".... I was crediting what you had already said, even if I didn't mention you by name.

So...

right back at ya

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Old 02-26-2008, 01:20 PM   #16
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Re: Fork oil change

The thing is I am very agressive on the brakes. I prefer doing all my braking before the corner rather than in it. I'm 198lbs and after setting static sag properly(23mm-3 lines showing) I use almost all the fork travel (2mm left). I probably exaggerated with 15w weight. Do I need different springs or a little higher oil level would be enough?

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Old 02-26-2008, 01:58 PM   #17
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Re: Fork oil change

Using damping to compensate for insufficient spring rate is a common mistake, but a big no-no. You want springs that will support the loads, which will allow the damping to be used for what it should be... control.

At your weight, I'd suggest .95Kg/mm springs... quite a bit heavier than what you've got. These will support your loads better, and keep you off the fork bottoms. Stick w/ the 5wt, and run an oil level of approx 130mm to start (keeping in mind that you'll want to fine-tune things as you go along). revalving the forks would help immensely, but you'd still want to start w/ the springs & oil level regardless.
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Old 02-26-2008, 02:17 PM   #18
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Re: Fork oil change

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Originally Posted by sportbike solutions View Post
i'm sorry if I didn't give you the credit you deserve, 1K. You most certainly did say the same thing, and it was excellent advice. That's why I said "I would also".... I was crediting what you had already said, even if I didn't mention you by name.

So...

right back at ya

Thanks! I wish you were a little closer. You seem to really know your suspension shiat. If only PA and AZ were neighbors....
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Old 02-26-2008, 04:17 PM   #19
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Re: Fork oil change

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Originally Posted by redlineK4 View Post
The thing is I am very agressive on the brakes. I prefer doing all my braking before the corner rather than in it. I'm 198lbs and after setting static sag properly(23mm-3 lines showing) I use almost all the fork travel (2mm left). I probably exaggerated with 15w weight. Do I need different springs or a little higher oil level would be enough?
first off: you are at td's so you must be wanting to hone your skills.

all your braking is not to be done prior to entering, just a majority of it then trail braking to the apex (for most corners)
-that is aggressive on the brakes.

otherwise it just sounds like you are improperly riding the bike and improperly using your brakes and just over braking for no reason.

I'm 210 and i use all my fork travel but i race and do a lot or hard riding with 7w oil and race tech internals that include .98 springs. Basically what you do is add a spacer (which I am going to be having done this weekend) to include more preload into the bike since mine is bottomed out and i still use the entire fork travel after last weekends race.
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Old 02-26-2008, 06:07 PM   #20
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Re: Fork oil change

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all your braking is not to be done prior to entering, just a majority of it then trail braking to the apex (for most corners)
-that is aggressive on the brakes.
Trail braking is not something I do not use but there are places like long straight followed by a very tight chicane where a lot of overbraking manevrous usually take place. All that matters there is who's got a larger pair of coconuts and brakes later. That's where my front suspension gets max load with rear wheel off the ground.
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