Changing Forks oil? Really!

[easyrider]

I read somewhere that the forks oil should be changed every so often , seasonally, or per mileage. To my thinking the forks are merely a shock absorber and the oil should be lifetime notwithstanding a seal failure resulting in leakage. The ones they use in automobiles never get changed and they are usually lifetime guaranteed. Whats the consensus ?? Curious to know.

[Old Grinner]

I think the fork oil can last a really long time . . ..

Some forks are a pain in the neck to change the oil because they don't have drain holes. You have to prop up the machine and remove the forks. The Kawasaki KLR is like that. I had a dealer replace mine some years ago. But then again the bike is going on 32 years old. My only problem with the front end has been an occasional need to tighten down on the steering head bearing. That said I figured the next time I replace it I'll do it myself. You just have to be careful removing the caps at the top.

Other forks have drain holes. At least with those all you have to do is remove the screws/plugs and push down on the front suspension to help eliminate it. Really have to make sure you get it all out though before you replace it. Just don't forget to replace those drainage hole screws . . ..

It's not like engine oil or final drive oil. But it can break down (thin out) and possible contamination exists. If you don't ride much in the rain or leave it parked outside all the time I'd say you reduce the risk of water getting through the seals. Keep the fork tubes clean/shiny and rust free and you won't have bumps eating away at the seals. I put fork tube protectors/shields on my Bandit. The KLR has gators.

Some people say change the fork oil every 10,000 miles or couple of years. It's a variety of opinions. On my XMax the owners manual says to check every 4K miles and look for leakage. Replace if necessary.

If you don't put a lot of mileage each year on your scooter and keep it garaged I think you should be able to go a long time on the original factory oil.

Here's more info from a previous thread here . . ..

viewtopic.php?f=22&t=5329

[easyrider]

Very helpful and well written reply. Thanks..seems like we are on the same page.. One also would think if it were meant to be changed regularly the manufacturer would provide an easy access drain plug or method for easy drain and refill without major disassembly work.

[Old Grinner]

I feel like an idiot . . ..

Correction:

1) My KLR 650 had the drain screws in the fork tubes. It's an early 1988 model. I think the newer KLR 650's after 2008 don't.

I had the OEM factory oil replaced back before 2000 by a dealer. I had to have a countershaft and sprocket replaced anyways so I figured I'd get the fork oil changed too. The early KLR's had smaller splines that wore out quicker on countershafts for the front chain sprockets. They changed the design not too long after. I've got almost 33K miles on it now and it still runs great. Here's a link to a vid (Part I) that shows the fork service procedure for an earlier KLR like mine. At around 2:00 minutes in he shows the oil drain screw but also continues with the process of emptying oil out through the top of the fork tube.




2)The Suzuki Bandit did not have the OEM fork oil changed yet. As you can see there is no fork oil drain screw on the 1998 GSF1200S.

100_6200a.jpg

I've got just over 30K miles on it now.

Either way just goes to show you I haven't changed any fork oil in years. But I do have official Suzuki oil on standby for when I do.

[springer1]

2)The Suzuki Bandit did not have the OEM fork oil changed yet. As you can see there is no fork oil drain screw on the 1998 GSF1200S.

I might be wrong but ..... is there a hole I see in the bottom of the fork leg, going vertical ? I’ve seen setups like that where the axle needs to be removed and then the drain plug is removed via screwdriver up through the hole and axle shaft.

[Old Grinner]

I might be wrong but ..... is there a hole I see in the bottom of the fork leg, going vertical ? I’ve seen setups like that where the axle needs to be removed and then the drain plug is removed via screwdriver up through the hole and axle shaft.

I think what you are referring to is what's called the "Damper Rod Bolt". It's not a drain plug per se. The hole to access it does go up through the center of the bottom each fork slider.

I've got the Haynes Service Manual that deals with both the 600 and 1200 Bandits at the time.

It states that fork oil replacement is a non-scheduled maintenance item in Chapter 1. It also states that the fork oil will degrade over time and lose it's damping qualities. In section 1-35 it also notes that "the forks fitted to these machines are not fitted with drain plugs . . . " and that basically you have to invert the forks to empty the oil out. The manual describes the whole process in Chapter 5 on how to remove and reinstall the forks for both models.

KLR

Drain Plug/Screw

100_6215a.jpg

Damper Rod Bolt

100_6221a.jpg

Bandit

No Drain Plug

100_6219a.jpg

Damper Rod Bolt Access Hole (axle needs to be removed)

100_6217a.jpg

[springer1]

Roger that.

[easyrider]

If the motorcycle oil degrades over time,then why do automotive shocks oil last a lifetime,and they support much more weight.?

[you you]

If the motorcycle oil degrades over time,then why do automotive shocks oil last a lifetime,and they support much more weight.?

Shock absorbers (dampers really) don't support any weight. The springs do, they are the shock absorbers.

A lifetime for a damper? There will be a huge degradation in performance by 10,000 miles but you won't notice or replace because you think they are lifetime. Somewhere between a mayflies and a tortoises.

[easyrider]

If you don't see any performance issue then they are still good.Most manufactures quote lifetime guarantees these days?? Shock absorbers do not support weight per se but do damper much more down force and lift forces than a fork on a 300 -400 lb bike that also has springs to support and dampen. My point is that if auto and truck shocks are lifetime with the same type of oil why do motorcycle forks which are shock absorbers essentially recommend oil changes .I suppose also todays shocks are gas shocks and have a different method of dampening. So then why don't motorcycles use gas forks ??

[you you]

A good performance upgrade used to be to dump the original fork oil as soon as possible and replace it with good quality oil a couple of grades heavier.


Lifetime is marketing speak as is gas shocks. When the oil wears due to shearing in a fork you change the oil because you can. When the oil wears due to shearing in a damper you replace it by replacing the damper.

[Inoplanetyanin]

If the motorcycle oil degrades over time,then why do automotive shocks oil last a lifetime,and they support much more weight.?

Automotive shocks don't last a lifetime at all. Not sure where would you get kind of notion.

The lifespan of a shock absorber depends on many conditions, like surface where the vehicle is driven, quality of material, unsprung weight of the suspension and on and on and on.

Most shocks need to be replaced anywhere from 60 to 90 thousand miles. In poor countries, in taxi cabs, they are replaced every few months.

I replace my scooter shocks oil once every few yrs.

https://www.strutmasters.com/when-to-re ... nd-struts/

[easyrider]

Everything has a wear factor , however I can only speak to my own experiences with shocks.. My truck was 11 yrs old and 150 k miles and the factory supplied shocks were perfect when I sold it. I suppose the oil in them was sufficiently doing its job and for many that would be considered lifetime of a vehicle. I suppose all cases are variable and relative to its environment but I think a routine change of fork oil may be overkill. I would think the springs would need to be considered as well as the oil once performance issues show themselves. Additionally , if the oil was to be routinely maintained one would think a drain plug would be provided.

[Inoplanetyanin]

Many big bikes, especially enduro and dirt bikes have drain plugs to drain the fork oil.

The oil in the fork gets contaminated when grit and dust passes the seals. Once dirty, oil starts to wear out the fork piston. Oil also breaks down, changes viscosity and prevents the fork from operating with designed parameters. Oil in the fork squeezes through narrow passages back and forth, providing damping effect. Contaminated oil and blocked passages, or oil that is too thin or too thick, can not allow the fork to perform as designed.

Hence oil change is necessary.

Please watch relative clips on youtube if you still have questions... https://www.youtube.com/results?search_ ... e+fork+oil

[easyrider]

Dirt bikes get dirty..hence drain plugs.

[you you]

Dirt bikes get dirty..hence drain plugs.

Fantastic clear statement.

So what is the connection from the expansive “bikes get dirty” .

Hence drain plugs?


Is it like dirt people, take showers, showers need drain plug.

Is that the argument solved?

[springer1]

I think the difference is ...... Auto / Truck shocks are sealed units and the internal oil compression pressure *IS* the designed dampening. A MC front end has a lot more travel / compression / volume and the designed dampening uses the small internal oil transfer ports at the bottom of the tubes, not just the oil compression pressure. .... and there's no way the larger volume of the compression in the top of the tubes doesn't result in some air bleed at the fork seals. That's why MC forks are only * Partially * filled with oil (designed to not foam) and partially with air. Anyone who has overfill the tubes with too much fork oil knows it will blow out the fork tube seals. So the minimal air bleeding in & out past the seals carries contaminants with it.

I figure the above is not completely correct, but some parts I know are correct.

[gn2]

Fork drain plugs have been removed as a cost cutting exercise.
Similarly grease nipples are gone.

[dick the den]

Its called progress.happens every where.

[Oyabun]

Some partially correct information, and some misunderstandings so far.
As someone mentioned, utomotive shock absorbers are sealed units, thus last londdr, but they are also not lasting forever. If you'd put a brand new and your "perfectly good after xx thousand miles" shock on a shock dyno (yes, there's such a device and professional suspension shops use them when working on racecars or motorcycles) you'd see a huge detoriation in damping effectiveness.
But the main difference is that of forks have a lot more functions and have to fave many more difficulties than shocks. Shocks have external springs and they are loaded only for axial stresses - read they only have to cope with forces along their axis. They also have lot shorter travel, usually more protected and have lot smaller sliding surfaces.
Contrary to this forks are
Internally sprung with long springs - which would buckle, if they would not be installed in the forks. But even if they cannot buckle, they are sliding on the inside of the stanchions, contaminating the fluid
Forks have whitstand all types of forces most of those would try to bend them while moving axially too so they get a lot more material removed from the sliding surfaces.
Forks have longer travel, larger sliding surfaces so they are contaminated faster.
Also they are less protected and flying debris and other contaminants (e.g. dead bugs) get swiped in to the fluid during suspension strokes.
And as others mentioned besides all of this the fluid has to provide not only lu rication,
ut damping also which shears the long chains of hydrocarbons while the fluid is pushed through the damping orifices. This hydraulic drag what provides damping, also heats up the fluid and all the contamination inside breaking it down and causing all kinds of issues like foaming, etc. what results in loss of damping and lubrication too eventually.
Therefore the fork fluid (and in fact shock fluid too) is advised to be changed in certain intervals. This interval depends on type and intensity of use just like your engine oil. Aftermarket shocks usually have 20-30k kilometers advised maintenance period and forks generally advised to be serviced also at these intervals if used normally. I usually suggest to change fork fluid every time when brake fluid is changed - which is every 2-3 seasons depending on use. But other applications have different regularity. For example track bikes usually have their suspension serviced at least every season, and dirt bikes much often than that especially if raced regularly.
Hope this helps.
P.s. Sorry for the typos and potential inconsistency, I'm writing from my mobile.