fork oil

[tjdziuba]

I bought a '94 Ninja 500 with about 12k miles on it. It's been running great for me.

The owner's manual says that the fork oil should be changed at 12,000 miles. I'd do it myself but I've read enough threads on people fucking up their suspensions and that such a thing should be left to professionals.

Anyhow, my question is, is the owner's manual just ballaching about changing the fork oil or should I really do it? Secondly, if I take it to a shop, how much would this cost me?

[altomista]

You should change it. Crap gets in there somehow and it needs to be changed periodically.

I had elskipador do my forks, and he took two hours to redo the entire thing (fork oil, springs, valve emulators). It should take less if you're just changing the fork oil.

[wsmc831]

100+ dollars usually, depending on the type of forks. yes, it's just as important as changing oil, brake fluid, coolant....better suspension = more control = safer.

[paroxysm]

Dave Moss once told me I should change fork oil as much as I change my engine oil. It works just as hard and needs to be taken care of. I think my mechanic charged me a little over an hour to do mine (just drain and re-fill, right?)

[ST Guy]

If you use high guality, synthetic, racing grade fork oil, for street use you shouldn't have to change it very often. Maybe once every 2 years. Or if you're fanatical, one a year. If you're looking for maximum performance on the track, then change it more often.

Use the very best oil you can possibly get. Amsoil makes some super good synthetic. Or if you just want to go to your local shop, ask for a synthetic racing grade. No reason to be cheap with fork oil as you aren't replacing it that often, it's really not that expensive, and you don't use that much.

Finally, do not simply drain the fork oil and put in the amount the factory says the fork requires. That's only a number to give you an idea of how much fork oil to buy. The ONLY proper way to do it is to follow the instructions in the manual and fill the forks to a specified level as measured from the top of the fork tube. This is most usually done with the springs out and the fork fully compressed. A lot of riders don't realize that small changes in the fork oil level can have a huge impact on how the fork works and feels. This is because as the fork oil leve goes up and down, so too does the volume of air trapped in the top of the forks decrease and increase. As the forks compress, this air compresses and acts as a second spring, supplementing the main coil spring. Fine tuning of the oil level in forks can be an effective means for fine tuning fork performance. For instance, if you're basically happy with the spring rate of your current springs, but find that the front end is a little closer to bottoming out on driveways, you could raise the fork oil level just a bit and effectively get a increase in resistance to bottoming towards the end of the fork stroke. Of course, you'd also be affecting the rest of the stroke, but the effect would be most noticeable towards the end of the stroke.

'Hope that helps.

[ST Guy]

Oh, I forgot to say why you don't want to simply drain and refill with a prescribed amount. That's because you can never be sure if you get all the old oil out. There's a lot that stays in the fork in spite of pumping and hanging upside down, etc. So when you put the "prescribed" amount back in, you're likely overfilling. Then each time you do it, the fork oil level gets higher each time.

The same goes for measuring the amount of oil that comes out and then putting the same amount back in. How do you know the fork oil level was correct before you drained it? It could have been set wrong at the previous fill. Or the level may have gone down from the original level due to leakage. Even with perfect fork seals, there's always a bit that get's by the seals as the fork is working. After many miles, the fork oil level will always drop.

So, always, always do it right and measure.

[tjdziuba]

Originally posted by ST Guy
Oh, I forgot to say why you don't want to simply drain and refill with a prescribed amount. That's because you can never be sure if you get all the old oil out. There's a lot that stays in the fork in spite of pumping and hanging upside down, etc. So when you put the "prescribed" amount back in, you're likely overfilling. Then each time you do it, the fork oil level gets higher each time.

The same goes for measuring the amount of oil that comes out and then putting the same amount back in. How do you know the fork oil level was correct before you drained it? It could have been set wrong at the previous fill. Or the level may have gone down from the original level due to leakage. Even with perfect fork seals, there's always a bit that get's by the seals as the fork is working. After many miles, the fork oil level will always drop.

So, always, always do it right and measure.

Yeah, I have decided that there are too many ways I can screw this up, so I'm going to leave it to a pro. I called Werkstatt this morning (BARF sponsor!) and they estimate about $158 for the job. Sounds fair to me.

[elskipador]

plan on 2~3 hours of shop time to do the job. i'd probably put 20wt fork oil in it to firm up the damping on those forks.

[MackeyStingray]

(just drain and re-fill, right?)no

[jim lindemann]

bring the forks in, we get about $60-$70 including oil. They are pretty easy to do yourself, might givver a go. I would recommend a set of springs while you have the caps off biggest single improvement you can make on that bike. $100.