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galenernest Mar 6th 2019 04:06 AM

Help! Fork oil level questions
 
6 Attachment(s)
Hi everyone,

The motorcycle is a Shineray X6, a 250cc four stroke dirt bike. Service manual doesn't exist as far as I can tell.

The front forks are made by a Taiwanese company called Fastace.

I blew a fork seal on my last ride, so I ordered new seals and fork oil and went to work replacing the fork seals. I found a site that said the forks take between 330mL and 380mL of fork oil.

I initially added 350mL of 10w fork oil to each fork. But, it didn't feel like there was any damping at all... I moved both compression and rebound damping to full stiffness and it didn't seem to change. So I went to the top of the suggested amount, 380mL and still it doesn't feel like there is any damping.


Should I add more oil? Did something go wrong? did I pour the oil into the wrong place? I poured oil directly down the aluminum upper tube (very light gold in color, the part that gets clamped by the triple tree) that can slide down once you remove the fork cap. There is also another cap (red, removed by turning the big rectangle inside the fork cap that when removed pulls out a short spring). See pictures.

I just think it's odd that I can't feel any damping after adding oil. Do I need to ride the motorcycle to get the oil to circulate? Or maybe try more oil? Help!

Sentinel Mar 6th 2019 05:35 AM

not more - heavier. IMO. oil flows through an orifice, a tiny hole. "more" oil won't slow that down. Heavier oil flows slower - more damping. More oil would shrink the air bubble above the oil, making the fork a bit stiffer as there is less compressible volume, unless it aint air tight, in which case it would just make it heavier. On all my old bikes I use a combination of old wasted oil and nasty water in my forks. Works great. </sarcasm>

mcrider007 Mar 6th 2019 06:31 AM

Quote:

Originally Posted by Sentinel (Post 53965)
not more - heavier. IMO. oil flows through an orifice, a tiny hole. "more" oil won't slow that down. Heavier oil flows slower - more damping. More oil would shrink the air bubble above the oil, making the fork a bit stiffer as there is less compressible volume, unless it aint air tight, in which case it would just make it heavier. On all my old bikes I use a combination of old wasted oil and nasty water in my forks. Works great. </sarcasm>

What he said....unless the recommended oil amount is so much understated that the current oil level is so low that the oil is not reaching the damping piston.

mgfchapin Mar 6th 2019 08:30 AM

10W is heavy stuff; the forks should totally lock up when the adjusters are screwed all the way in, ASSUMING they actually do something. I have seen plenty of expensive Japanese bikes with adjusters that didn't do much, so I wouldn't be surprised if those on Taiwanese forks are equally useless.

When you refilled the forks with oil, did you pump them up and down a dozen times to get all the air out?

I wouldn't go by a quantity of fork oil to add. Are you sure you drained all the old oil out? Is that spec with the forks completely dry and disassembled, or simply an "oil change" refill? The only sure way to do it the first time is to get or make an oil level gauge like this one: https://www.motionpro.com/product/08-0121 If you take the cap off, can you see any oil? Are you able to at least measure the current oil height with a thin ruler? The air gap from the oil to the top of the silver tube, depending on fork brand, is anywhere from 70 to 180 mm. More likely it's on the lower end of that, so maybe start with 90 mm and see how the damping feels.

Once you've set the height accurately, in the future, you can drain the oil into a graduated cylinder or measuring cup and put the same amount back in.

curve addict Mar 6th 2019 08:50 AM

Since you have already poured 380ml in; I would suggest that you open up all damping screws all the way and start pumping. If you start to get some damping, give it a ten+ minute rest, to bring bubbles to the top, and repeat.

My memory tells me that there are a couple types of forks that do require that x-amount of oil be poured into an upper chamber, during assembly. The viscosity of this oil can also be different than what goes in the main body. I have worked on that style, a time or two, in Arizona. I can't remember which ones, or their specs, right now.

DGA Mar 7th 2019 06:20 AM

As MG' said, measuring the height is the best way to go. If you've got a manual for that thing, it should say what the height is and what should be in the fork before taking it, spacer, spring, or whatever. And again, as said below, make sure to charge the cartridge with oil by pumping the assembly up and down.

Squidly Mar 10th 2019 09:33 AM

Lots of good advice here.

Air gap doesn’t make a big difference. Less air gap means the fork will be stiffer right before bottoming out which is good for bikes that hit bumps hard and things like that, but for 90% of the fork’s travel you won’t feel a difference in damping with different air gaps (within spec).

It sounds like theres air in the damper.

galenernest Mar 12th 2019 04:39 AM

Ok, thanks for all the advice so far, guys. I'm going to disassemble the forks again because both of them started leaking on my first ride since replacing the seals. So I did something wrong or I got really cheap seals... I can't think of anything that could go wrong, though... I used plastic bags to slide the seals over the fork tubes and everything went together just as it came apart... maybe I need to replace the bushings as well?

Headache, but yeah I want to get this fixed correctly.


Is it possible that I just pushed them too hard? The ride I did on Sunday was really hard on the bike... lots of rocks and boulders, and even up and down a staircase built out of rocks... I don't really know why they would leak again other than the seals were too cheap (I think I paid around $6 each for them) or I'm just hammering on the front suspension too hard when I ride?

curve addict Mar 12th 2019 10:07 AM

If the oil level was too high, and the air gap effectively disappeared when the fork bottomed-out, then hydro-lock could have pushed the oil past any seal. Generally speaking, Japanese manufacturers, at least, take this into consideration when recommending oil quantities, even if the parts were previously wetted. Even at maximum recommended oil fill, this would not normally happen. Without a doubt, knowing and sticking to a known, proper oil level will help prevent this; if the given specs are correct.

At this point, I would expect that the seals are sub-standard.

If this bike is a copy of something Japanese, I suggest that you find the appropriate, Japanese, service instructions for the fork and follow those instructions.

In the past, when doing spring and valving changes on older machines, I would measure the amount of oil that the new, dry spring displaced when dropped into a cylinder of oil (made out of PVC pipe and a cap). Then, I would assemble the fork leg, minus spring but including all other components, compress the leg fully, and fill the tube to the point where the bottom of the top plug would reach. Get all of the bubbles out, let it sit a while and do it again.
Then, I would draw out oil from the tube until it reached my intended, fully-compressed, air gap. Lastly, I would pull out the measured amount of oil that the spring displaces, dry the spring and put the spring in place, and assemble the unit. Using quality parts, I never had a failure that I know of.

mxmike Mar 13th 2019 11:42 AM

I'd disassemble one of the fork legs and take it down to a motorcycle shop or suspension tuner. The fork is probably a Showa or KYB knockoff with an inner chamber that needs some oil added to it. They can probably tell you what's going on.


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