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humpness

fork oil amount

13 posts in this topic

should i go different from what the manual says? I have 2liters of belray 5w waiting. I am wondering this because i weigh a little heavy on the stock springs. 190-195 wo gear. trails + mx. i hope i have enough oil.

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  1. We don't know what you're thinking of doing differently than the manual
  2. We don't know what kind of bike you're working on (year/model?)

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Right.

I want to know if I should put more or less oil in the forks than the manual says. 2007 yzf450f.

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Well, I've got an '09 and I run 360ml in each outer tube. The 2nd last time I serviced my suspension I thought I'd start with 350ml but found it was too soft & I had to increase my comp. dampning. I bumped up to 360ml (compressed/released the fork(s) and added 10ml through the air bleed screws) and am happy there.

I weigh 210Lbs and am running DSP springs front 0.50kg/mm and back 5.8kg/mm. I ride MX only. I thought the suspension was good stock, then I put the springs in & now I LOVE it !

If you're just putting fork oil in the tubes, 1 liter is more than enough.

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In the damper cartridge, you cannot put more than it calls for because it calls for being completely filled. If you put in less, then there's air in it and it doesn't work right.

See:

Bleeding KYB Fork Cartridges

Jam nut "gap" explained (hopefully)

In the outer chambers, the manual calls for 350cc of oil. The fork is very sensitive to changes in this level, and more oil makes it harsher very quickly, while less makes it it plusher, but can cause bottoming. If you use a 2.5 to 5wt oil, start with 340, and add 5cc at a time if it bottoms excessively or harshly.

What I do is use a heavier oil in the outer chambers and run less of it (315-325cc). The oil in the outer chambers does no damping, so the heavier oil has no effect on the feel of the fork. But it does lube the main tubes and it provides the cushion that prevents harsh bottoming in the last inch of fork travel as it is forced through the oil locks. Lowering the oil level gives a plusher ride, while the heavier oil increases bottoming resistance to make up for the reduced "air spring".

I also recommend this simple mod to reduce the possibility of breaking the free piston:

http://www.smartperformanceinc.com/YZMODASSEM.htm

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The 07 calls for 340cc of fork fluid in each outer chamber. 2 liters is plenty of oil, you'll have about half a bottle left if you do the inner and outer cartridges in both fork legs.

Try starting at 325cc in both outer legs. Ive tried 340 and it always felt stiffer than stock, regardless of the oil weight 7w or 5w I was using. If you want less dump the oil back out into a ratio rite and suck out 5cc at a time with a syringe. If you need more just take the top cap off again and add it. Tusk , makes a set inner and outer fork cap wreches for 20 bucks from rockymountainmc.com Awsome. It fells great to do it yourself and save the 280 bucks that a shop charges.

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i had to stop early because my tool is a motion pro fork wrench and it didnt come with a nut for inner cartridge. any ideas? im headed to the hardware store tomorrow to look around. so far i got the seals on but im dead in the water until i find something. ill need a four sided nut at 1" or an 8 sided nut at 1 3/8". come to think of it i bet a 5/8 DA nut would fit.

Edited by EOYZF

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Again. Tusk , makes a set inner and outer fork cap wreches for under 20 bucks from rockymountainmc.com Best deal around.

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i gotcha. again, i screwed up and got the wrong wrench without the nut. for now i want something that will "work" as far as taking it apart. if not ill just put it back together without draining the inner cartridge because i want to ride. ill get that tool later. follow?

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Here's a redneck cheat for you:

One of the members here states that he used one of his rear axle blocks inserted end-wise into the base valve pocket and unscrewed it by turning the block with a crescent wrench. Not recommending it, but....

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hell ya i think that makes since now. so if you the put the block in "upright"? I dont want to do this but atleast now I have options if i cant find something at the hardware store. thanks gray.

is the inner cartridge completely sealed off? I am wondering if any oil may have drained out in case i cant get it open and want to put it all back together.

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The inner cartridge is totally sealed, BUT, they can leak in a couple of places in a couple of ways.

The seals of the free piston (white plastic piston in the mod link I posted) can leak and let the piston fill with oil, eventually causing it to break. The rod seal can leak fluid out the bottom into the rest of the fork, but they're usually pretty durable.

Much more commonly in those forks that are bottomed often, the rod seal lets outer chamber fluid into the cartridge, which temporarily overfills it. This happens as the nose of the cartridge is rammed down into the oil locks that prevent metal-to-metal bottoming. The pressure against the seal increases sharply when that happens. Normally, the excess is simply blown out the top through the bleed holes, same as in the bleeding process, and it's a non-issue. If you use two different oil weights, though, this does mean that they become mixed over time, and may need to be changed more frequently.

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is the inner cartridge completely sealed off? I am wondering if any oil may have drained out in case i cant get it open and want to put it all back together.

Yes, the inner chamber oil is completely seperate from the oil in the fork tube (outer chamber). The only way oil can migrate is if you have a leaking ICS seal or a leaking cartridge (dampner rod) seal. If either are leaking you'll know for sure when you remove the inner cartridge from the fork leg/tube. If you compress the rod into the cartridge and it only returns a few inches, then you've more than likely have a seal that's blown. If it returns all the way, or pretty damn close then you're good.

:thumbsup:

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