Fork Oil Level

[TahoeBound]

Looking for confirmation on fork oil level with the bike on the centerstand, caps & springs removed and forks fully compressed (or as fully compressed as can be on the centerstand).

Is there a large difference in oil level versus when the forks are pulled off the bike and fully compressed?

My intent is to change/experiment with different fork oil weights, but would not want to completely pull the forks in order to experiment. However, going in from the top is not too bad. Then just suction out and refill with different weight. Good or bad idea?

TIA

 

[FJRay]

I don't think you can change fork oil with the forks in place. You might get some of it but not all. Mine are hanging upside down at the moment while the Kerosene used to flush them drains out. It is easy to remove the forks so why not do it right and then you experiments will be usefull.

 

[Geezer]

I don't know how much you can get out by suctioning it out from the top, but as long as you measure the level before you remove any, then top it off to the same level when you put in the new stuff it should work for you.

 

[yamafitter]

...My intent is to change/experiment with different fork oil weights, but would not want to completely pull the forks in order to experiment. However, going in from the top is not too bad. Then just suction out and refill with different weight. Good or bad idea?

TIA

Bad idea. The forks should be removed and with the caps and springs removed it is important to "pump" the forks at least a couple of times since the valving in the forks causes some of the oil to be held up. The time tested way is to stroke the fork while inverted to get the oil out and then flush with solvent again stroking the fork to remove any residue.

Fork oil gets contaminated fairly easily and it is important to start out with nice clean oil or you are basically wasting your time IMHO.

 

[SLK50]

IMO, "experimenting" with different weight fork oils is a waste of

time and money since the fork is adjustable for compression and rebound.

You can simply adjust to compensate for the change in oil weight

thus negating the effect of the oil alone.

Is there as aspect to this that I have missed?

 

[08FJR4ME]

IMO, "experimenting" with different weight fork oils is a waste of

time and money since the fork is adjustable for compression and rebound.

You can simply adjust to compensate for the change in oil weight

thus negating the effect of the oil alone.

Is there as aspect to this that I have missed?

Never thought of it that way but it makes sense.

Dave

 

[HaulinAshe]

There are significant characteristics associated with various fork oil weights on the FJR. It is true that the OEM/stock valving provides enough range to compensate for most of the differences between UltraLight 2.5 wt oil, all the way to Heavy 15 wt oil. It's at the extremes of the spectrum that fork oil weight makes a huge difference, and valving has little effect.

You will find that UltraLight(2.5 wt) to Light(5 wt) grades provide the most ride comfort for the top of the travel. When you install higher rate springs (> .90 kg/mm) the lighter weight oils don't provide enough rebound damping to counter the stronger spring rates. That's typically when people try using heavier weight fork oils (10-15wt). Unfortunately they find they have traded the ride comfort that soaks up pavement ridges and slab pounding for better performance in the deep strokes of hard twisties.

Your original question was about replacing the fork oil and checking the level without removing the forks. It can be done. You will have to drain the oil, pump the damping rods to expel fluid, and repeat the process many times to remove all the old fluid. Refill and pump the damping rods several times again to remove all the air and ensure the cartridges are completely bled of air.

As for oil levels... You will find that it takes about 20mm change in oil height to feel a noticeable difference in fork behavior. I would stay within a range of 85-120mm, with 100mm being the most commonly used level. Assuming stock springs... Above 85mm and you risk hydraulic lock in heavy strokes. Below 120mm and you expose the top of the cartridge in rough conditions, causing air to bleed into the cartridges and excessive upper cartridge bushing wear.

Shoot me a PM if you want advice on how to possibly accomplish a specific change you're after. Suspension setup is all about compromising in one area, to achieve what you want somewhere else.

 

[spike747]

I don't think this is a good idea at all. I'm not sure how many fork oil changes you've ever done, but you'll never be able to get all the old stuff out from the top, even if the forks are fully compressed. With all the moving parts inside there's a bunch of "material" that can build up at the bottom of the fork. Otherwise the oil would come out looking brand new. You probably will only be able to remove about 70% of the oil. And the rest at the bottom is the dirtiest of all the oil. You wouldn't drop 70% of your engine oil at oil changes. Why do it for the forks.

Also, after I've drained all the old oil out I usually put about 1/2 litre of new oil inside the fork and pump the cartridge a bit. When that 1/2 litre of oil comes out, its usually VERY dirty. Again, syphoning from the top won't get any of this material out.

I bet changing oil like this won't save much time at all. Not to mention the mess you could make all over the bike. I'd take the time to pull the front end off. It's only about an extra hour. And if your reasoning for doing this is cause you're not sure how to hold the front end up with no front wheel, there's lots of idea here on how to hold your front end up. There's only about 30-40 pounds of weight on the front when on the center stand.

There's lots of areas you can cut corners on repairs on these bike, but I don't think this is one of them.

 

[spike747]

IMO, "experimenting" with different weight fork oils is a waste of

time and money since the fork is adjustable for compression and rebound.

You can simply adjust to compensate for the change in oil weight

thus negating the effect of the oil alone.

Is there as aspect to this that I have missed?

This is true to a certain extend. The valving is designed to work with a specific range of oil weight. Even the primitive inners of the FJR forks. The clickers are a way of fine tuning the dampening so they have a limited range. If you went too thick in the oil, you'll get hydrolock where the oil can't physically flow quick enough through the orifices. If you go too thin and the valving's not really doing much at all.

But I do agree that experimenting with different weights is a waste of time. First thing I do on a bike (dirt or street) is replace the springs to match my weight. Dollar for dollar, the absolute best mod I've ever done on suspension. And when you consider fork springs usually go for about $100 a set, its a cheap upgrade too. Suspension needs to be setup so that sag is 1/3 of the way into travel when you're on the bike. Once that has been attained, the valving can actually do its job the way the factory intended.