Topping out....

[ecoast]

It seems as though the front forks on my as-new gy-5 are topping out at full extension; with a hearty 'clunk'

annoying.

I have seen some of the posts on changing fork oil and/or adding pre-load spacers, anything else to consider?

Does not seem to be much dampening going on...

sounds kind of 'cheap' (because it IS, lol)

[Wild_Alaskan]

add two cap fulls of heavyish weight fork oil or some 10w-40 to each fork, this usually solves the problem

[SpudRider]

You can also increase the amount of oil in each fork. The Chinese forks seem to have very low levels of fork oil. :roll:

Spud

[ecoast]

...so add an ounce of 10-40 per leg and give it a go, eh?

[dmmcd]

If you're topping out, you don't want to add any preload spacers. Heavier oil will definitely help slow the rebound.

Can I ask how much you weigh? I am only 140 lbs, and have the opposite problem on my XF200. I've only topped it out over jumps, but it compresses quite readily and dives under braking. I keep meaning to change the fluid, but just haven't gotten to it yet.

[ecoast]

approx. 200 lbs, all up.


was not going to add spacers yet; looking to smooth operation at full extension first...

Who knows; may be NO oil in there...

[dmmcd]

Originally Posted by ecoast

Who knows; may be NO oil in there...

That's the way my forks feel most of the time. I'll open them up eventually, but the bike still goes so I don't feel like disabling it for a day or two while I fuss around with the forks.

[zingshoen]

wild alaskan said it. it s the oil, too little of it, it always is. :-) a manual would tell you how much, might as well fill em up properly. on the zong its 200 ml. i ve used a C4 auto transmisson oil with great success but they also have fork oil in the shops.

[david3921]

I know that some (like zingshoen, above) have used ATF with sucess but my opinion is to go with true fork oil. That way you know the weight in case you have to go up or down. I measured the fluid that came out of my XF200 forks and they were 330ml each like the manual says there should be. I went with 20w fork oil with some sucess...I was looking to eliminate some of the diving during braking. I will add more oil, a fluid ounce (about 30ml) at a time, if I need to fine tune the forks.

[Weldangrind]

I believe that fork oil is simply non-detergent oil. I've experimented with 10W, 15W and 20W non-detergent oil in forks with good results. It's usually half the price and twice the volume.

[SpudRider]

I agree with Weld, Zingshoen, and David.

If non-detergent, SAE motor oil works well in your forks, there's no reason to spend more money for fork oil. However, David is certainly correct. Fork oil is formulated to maintain a consistent, known viscosity over a wide temperature range. In contrast, SAE motor oil has a wide range of viscosities, as shown in this chart.



Also, fork oil has anti-foaming agents, and other additives to reduce fork stiction, et cetera. However, two, 10W fork oils can have very different viscosities, as shown in the following chart.



Therefore, some 10W fork oils actually have a lower viscosity than some 5W fork oils. 8O To make sure you are actually getting a higher, or lower viscosity, you need to verify the data.

I chose Mobile1 Synthetic ATF when it came time to change my Zong's fork oil, and it is working great! This particular ATF is so frequently used as fork oil, it's viscosity is know to be 34 cST at 40C. Like fork oil, Mobile1 Synthetic ATF has a high viscosity index, meaning it retains its viscosity over a wide temperature range. The Mobile1 Synthetic ATF also has anti-foaming agents, and provides low fork stiction. I also like Mobile1 Synthetic ATF because it helps to clean the old fork oil from the forks, doesn't get dirty like fork oil, and is less expensive than fork oil.

The 34 cST viscosity is working very well in my forks; they are less stiff than before. The Mobile1 Synthetic ATF is roughly equivalent to a 10W fork oil, so the original, Chinese "fork oil" must have had a higher viscosity.

In the final analysis, I agree most with David. If you want to fine tune your forks, it's best to use fork oil, since you can mix known viscosities, and produce the exact blend you desire. Also, fork oil does have extra additives which make it superior to regular motor oil. However, if non-detergent motor oil works well for someone, I don't see a reason to switch to more expensive, fork oil.

Spud

[Krasi_BG]

Originally Posted by SpudRider

...is formulated to maintain a consistent, known viscosity over a wide temperature range. ...

This seems to me like a definition for ATF, or power-steering fluid, or in fact any good hydraulic oil

[SpudRider]

Originally Posted by Krasi_BG

This seems to me like a definition for ATF, or power-steering fluid, or in fact any good hydraulic oil

Not all fork oils, ATFs, or hydraulic oils are created equal, Krasi. Check the viscosity index (VI) for the various fork oils in the chart I posted. You might also enjoy reading the information at the following link.

http://www.peterverdone.com/wiki/ind...spension_Fluid

Mobile1 Synthetic ATF has a good viscosity index, but many of the fork oils have even better VIs.

Spud

[SpudRider]

As I related earlier, Chinese motorcycle forks are notoriously low on oil. :roll: After reading conflicting information from several Zongshen service manuals, I finally decided to add 200ml of fork oil (Mobile1 Synthetic ATF) to my Zong's forks.

http://chinariders.net/modules.php?n...wtopic&t=13268

My forks are working great, but after adding 200ml of fork oil, the fork oil level is 11.5-inches, or 292 mm from the top of the compressed fork. :? Therefore, I’ve decided to add fork oil until the oil level is 150mm from the top of the fork tube, or the oil covers the top of the fork spring. I plan to raise the fork oil level about 142 mm. Therefore, I will probably add about 130ml of fork oil to each fork, for a total of 330ml of fork oil per fork. Incidentally, the Qingqi service manual specifies 330ml of fork oil for the QLink forks.

You can set the fork oil level to the desired height utilizing a turkey baster.



No, not that kind of turkey baster. :roll: This is the type of turkey baster you should use to establish the correct height of your fork oil.



You can employ the turkey baster in the following method, marking the baster for the desired height of the fork oil.



In my instance, I will see how much additional fork oil is required to cover the fork springs. Then, I might add as much fork oil as necessary to bring the oil level to 150mm from the top of the compressed forks.

Spud

[SpudRider]

As motorcycle forks compress, the amount of air above the fork oil is also compressed. Therefore, having too much air above the fork oil can allow the fork to bottom out too easily. Increasing the oil volume inside the fork also increases air pressure in the sealed fork unit, helping to prevent the forks from becoming too spongy. Of course, it's also important not to add too much fork oil, or the pressure could become too high inside the forks, damaging the fork oil seals.

Leaving 150mm (5.9-inches) of air space should not cause excess pressure inside my Zong's forks. However, reducing the air space from 292mm to 150mm will probably make my forks more resistant to bottoming out.

Spud