Fork oil viscosity, experiences?

[kjetil4455]

Hi guys

I have already searched on the forum regarding this topic, but I have to ask anyway. I find the general consensus that stock fork oil viscosity is 5W, the Yamaha Fork oil 01 equivalent.
Well, my suspension is stiff as hell on that oil. Very, very stiff. When I got the bike, suspension was incredibly soft -- too soft. Comfortable, but not very off-road capable. I upper it to 15W, which was way too much and it hydrolocked. Took it down to 10W, still too much. Took it down to 5W -- expecting success, but compression is still very hard even at ZERO clicks (ie. max clicks out). Rebound is also a tad slow despite 0 clicks (again, max (10?) clicks out).

This has made me wonder if 0W or 2,5W is the true equivalent to Yamaha's 01 fork oil. The oil changes were done at yamaha and my fork is in mint condition. Unfortunately they don't have the stock oil available, and also (I live in Colombia) don't have a lot of experience with this specific bike.

Have anyone experienced what I am experiencing?
I am planning to bring it down to 2,5W and, worst case scenario, 0W. Already spent 300 bucks on erroneous trials.

 

[Tenman]

How’s your sag?

 

[escapefjrtist]

Check HERE for comparable oils. My latest change was Maxima 85/150 which (viscosity wise and fork action) compares with OE suspension fluid. When changing fluid, do confirm shop is purging the damper assembly before and after fluid change.

Good luck!

~G

 

[Jlq1969]

Check what Tenman says…..Preload (nut)….Sag/rebound (screwdriver)…or maybe a valve locked…

 

[kjetil4455]

How’s your sag?

sag is 6cm, it's correect. preload is zero

 

[~TABASCO~]

The "weight" is only one part of the "pie"..... how much did you put back in ? Did you check the distance from the top if the fork to the bottom of the oil? How exact did you get this ? I believe stock you do this with the springs still on the cartridge.... I believe the Ohlins you do this with the springs off (or vise versa).... You can change the weight and get results.... and you can change the 'air volume' or oil volume and get totally different results. On the Tenere I have played with both oil weight and volumes 8-10 times before.... I have a whole book of notes.....

If you have stock forks, and stock springs, Etc...... I probably would suggest the stock weight (5) and then increase the oil volume slightly... you can always increase or decrease the oil for different effects......... Think of that top air pocket as a second spring... an 'air spring'...

You can also keep the stock weight and stock height (oil) and then just change to a straight wound coil spring.... that will help the Tenere a lot....

Each time you mess with the oil make sure that its at the correct height with a "suspension syringe"... If you're guessing or "winging it" your quality of ride will be all over the board.....

Im a bit of a service nerd and particular.... I spend several hours getting all the air out of the compression and rebound cartridge (so I can get the most accurate reading) and then make particular care to get the correct volume in each leg, checking and re checking... I have past notes on what I had, what I might want to change and then write down the new notes..... It's important to have the "correct volume"........

 

[gv550]

Fork oil level is measured with the fork fully compressed and without the spring. I use kyb 01 fork oil and .95 constant rate springs from Sonic.

 

[kjetil4455]

Could it be that my yamaha tech poured too much oil in there?
Manual says 505mL per side, as far as I know, so we separated one liter equally into 500mL on each side. We didn't measure, only followed the volume specs.

However, it has been my understanding - and correct me if I am wrong - that oil volume has more to do with total travel, whereas oil viscosity determines the ease or difficulty of travel (ie. the amount of friction generated as the oil passes through the valving). How would reducing oil level increase traveling speed / ease of the fork? Thanks

 

[kjetil4455]

Sorry to double post, but I found this online

"What is the effect of changing oil height? Adding oil to your forks reduces the air volume. Since air is compressible, a smaller airspace is harder to compress than a larger airspace, which results in a stiffer fork. Since the compression of the airspace is gradual, lessening the airspace will be felt by the rider from the middle of the fork’s stroke to the point of bottoming. In essence, adding oil to your forks makes them stiffer from the midpoint on. The obvious corollary is that when you take oil out of your forks, you make them softer from the midstroke on. Adding or subtracting oil has a negligible effect on the first four inches of travel. " https://motocrossactionmag.com/how-to-fix-your-forks-with-fork-oil-height-tricks/

If this is true, then I am confused, because my fork is stiff from the get-go, not from mid-stroke and down. even small bumps feel stiff.

 

[~TABASCO~]

Could it be that my yamaha tech poured too much oil in there?
Manual says 505mL per side, as far as I know, so we separated one liter equally into 500mL on each side. We didn't measure, only followed the volume specs.

However, it has been my understanding - and correct me if I am wrong - that oil volume has more to do with total travel, whereas oil viscosity determines the ease or difficulty of travel (ie. the amount of friction generated as the oil passes through the valving). How would reducing oil level increase traveling speed / ease of the fork? Thanks

Could they put too much oil.......................... Yes. for sure.... There also could be air in the cartridge that can create a temporary 'air lock'..

What did they do for you ? Just changed the oil ? Did they fix a seal or clean up / clean out the cartridges ?

Do you know if they "re set" all your settings properly to where they were before you dropped it off ?
( keep in mind, that sometimes a rider might add more compression and rebound as the oil deteriorates.. Sometimes the settings have to be 'backed off' a little to compensate for new oil / weight of oil . If these are kept the same and some of these items changed the ride feeling will for sure change )
The air gap at the top is basically a second air spring. So that volume of air has an effect on the overall performance. (more or less oil, effects more or less air volume)

Yes the weight of the oil will have an effect on compression and rebound when going through the valves.. But also keep in mind the factory preload / compression / rebound settings......... Have these all stayed the same ?

 

[kjetil4455]

Rebound, compression and preload are all set on 0 -- fully open (ie minimum). It is stil very, very ridig.
I am starting to think that there might be somethinge else going on here than mere oil viscosity. Maybe stiction (although the mechanic is very experienced -- but we can torque it), maybe oil level, maybe stuck valves (although the screws do seem to affect dampening, and they never had any issues before). The suspension was incredibly soft when I bought it. Technically I am now, again, on stock settings, and it is hard as well. Something's gotta be off.

We'll start by taking 10cc out of each fork and see what happens, it is the cheapest and easiest way to proceed at this point.

 

[gv550]

I have a friend who took her bike to a dealership to replace fork seals and maybe bushings too. Her forks were almost rigid and very uncomfortable to ride, took it back and the tech assured her it was repaired properly. I took the forks off and discovered the dealer set the oil level (air gap) with the forks extended. I reset the level properly and problem solved, actually too soft for my liking but just how she likes it.
505 ml oil volume is only the initial fill quantity, remove oil to obtain the correct oil level (airgap).

 

[~TABASCO~]

Rebound, compression and preload are all set on 0 -- fully open (ie minimum). It is stil very, very ridig.
I am starting to think that there might be somethinge else going on here than mere oil viscosity. Maybe stiction (although the mechanic is very experienced -- but we can torque it), maybe oil level, maybe stuck valves (although the screws do seem to affect dampening, and they never had any issues before). The suspension was incredibly soft when I bought it. Technically I am now, again, on stock settings, and it is hard as well. Something's gotta be off.

We'll start by taking 10cc out of each fork and see what happens, it is the cheapest and easiest way to proceed at this point.

I think I know what might be going on.... Ive seen this before..... What service did they perform ? Do you know what they did exactly ? Did they remove the spring off the cartridge for any service ?


Yes I agree... you have something else going on........

 

[kjetil4455]

I have a friend who took her bike to a dealership to replace fork seals and maybe bushings too. Her forks were almost rigid and very uncomfortable to ride, took it back and the tech assured her it was repaired properly. I took the forks off and discovered the dealer set the oil level (air gap) with the forks extended. I reset the level properly and problem solved, actually too soft for my liking but just how she likes it.
505 ml oil volume is only the initial fill quantity, remove oil to obtain the correct oil level (airgap).

That sounds like what might have happened here!

 

[~TABASCO~]

That is what might have happened................ (above post.... to much oil)

For folks that have removed the spring off the cartridge... There is a jam nut at the bottom of the top cap. If the rebound screws are not set a certain way before reinstalling the cap/jam nut it can virtually "lock out" the cartridge and give you the characteristics you describe.... To fix this, the jam nut needs to come back off, re set the rebound up properly for 're installation', and then re tighten the jam nut.. This will allow the compression and rebound to work properly again (On stock forks) (this rebound needs to be set up per the book for the installation, and after the fork is assembled then it can be adjusted to the riders preferences.... )

 

[kjetil4455]

That is what might have happened................ (above post.... to much oil)

For folks that have removed the spring off the cartridge... There is a jam nut at the bottom of the top cap. If the rebound screws are not set a certain way before reinstalling the cap/jam nut it can virtually "lock out" the cartridge and give you the characteristics you describe.... To fix this, the jam nut needs to come back off, re set the rebound up properly for 're installation', and then re tighten the jam nut.. This will allow the compression and rebound to work properly again (On stock forks) (this rebound needs to be set up per the book for the installation, and after the fork is assembled then it can be adjusted to the riders preferences.... )

That's very interesting. we did change the spring twice; maybe it locked the first time and the mechanic never noticed.

 

[~TABASCO~]

That's very interesting. we did change the spring twice; maybe it locked the first time and the mechanic never noticed.

It’s easy to get the jam nut re installed with the top rebound in the wrong position. Only after (someone) gets it back on the bike do they realize what is wrong- have to take it all apart again. You can always check to see if it’s “correct” by counting the clicks on the rebound. It should be the exact number from the service book. If it’s off even by one click- the jam nut is not correct……

 

[cyclemike4]

That is what might have happened................ (above post.... to much oil)

For folks that have removed the spring off the cartridge... There is a jam nut at the bottom of the top cap. If the rebound screws are not set a certain way before reinstalling the cap/jam nut it can virtually "lock out" the cartridge and give you the characteristics you describe.... To fix this, the jam nut needs to come back off, re set the rebound up properly for 're installation', and then re tighten the jam nut.. This will allow the compression and rebound to work properly again (On stock forks) (this rebound needs to be set up per the book for the installation, and after the fork is assembled then it can be adjusted to the riders preferences.... )

Next time in my forks I will have to pay close attention to that! thanks. I need to service them soon!

 

[kjetil4455]

It’s easy to get the jam nut re installed with the top rebound in the wrong position. Only after (someone) gets it back on the bike do they realize what is wrong- have to take it all apart again. You can always check to see if it’s “correct” by counting the clicks on the rebound. It should be the exact number from the service book. If it’s off even by one click- the jam nut is not correct……

That's interesting. Any chance you can show me what the jam nut looks like?
I seem to have some slight differences in clicks, don't remember exactly but I believe that both on compression and rebound that one had 9 and the other 10 or something like that.

 

[~TABASCO~]

That's interesting. Any chance you can show me what the jam nut looks like?
I seem to have some slight differences in clicks, don't remember exactly but I believe that both on compression and rebound that one had 9 and the other 10 or something like that.

Compression is on bottom and doesn't have anything to do with the 'nut'....... the rebound is on top and L & R should be the same (on stock forks) I thought It was like 13-14-16 clicks... (I would have to check in the book)