fork preload

[ReapeR]

at the end of the summer last year my right fork seal was leaking, so i took it off and took it to my dealer to let them put a seal in it and i ordered new clip ons then too, when i got it back before i could put the new clip ons on it i had to lower the other side a little more, then put the other one back in i measured both of them and they are the same, but you know how it feels when you go across the lines in the middle of the road!? that wobble? it feels like that all the time, and its riding to the side of the tire. so how can i adjust the pre load on the fork cuz that side feels alot softer than the other side now, and im about 98% sure both of them are the same height, i measured before i put the bars of then from the inside of the bar after. i havent rode it in a couple months and got on it the other day and i had forgot about it and it almost threw my a$$. thanks for any help in advance if i cant get back on today.

 

[blu3]

at the end of the summer last year my right fork seal was leaking, so i took it off and took it to my dealer to let them put a seal in it and i ordered new clip ons then too, when i got it back before i could put the new clip ons on it i had to lower the other side a little more, then put the other one back in i measured both of them and they are the same, but you know how it feels when you go across the lines in the middle of the road!? that wobble? it feels like that all the time, and its riding to the side of the tire. so how can i adjust the pre load on the fork cuz that side feels alot softer than the other side now, and im about 98% sure both of them are the same height, i measured before i put the bars of then from the inside of the bar after. i havent rode it in a couple months and got on it the other day and i had forgot about it and it almost threw my a$$. thanks for any help in advance if i cant get back on today.

You can't adjust the preload on stock FZ6 forks.

Complete guess here, however, from what you are saying you took one of the fork's to get the seal replaced in which case the dealer more than likely replaced the fork oil while they were at it. Which means that you have new oil in one fork and old oil on the other fork, possibly with a different weight as well, maybe even a lower/higher amount than the other fork. That would explain the what you are experiencing. If I were you I would replace the fork oil on both to start off with.

 

[Erci]

Something else is going on here.. it's not because "one leg is softer than the other". Some forks use spring in just one side and all the damping is done on the other side.

I would start by checking the head bearing.. make sure there is no play in it and that it's not too tight.

Check the tire.. make sure it's in good shape and pressure it in proper range.

 

[Erci]

Oh and your bike looks awesome! :thumbup:

 

[ReapeR]

ok thanks, ill change the oil in both and try that. and thanks ive worked hard on it, it still needs some work but its one of a kind.

 

[MattR302]

One of your tires could be out of balance. Or the rear wheel's not aligned right.
If it was riding fine before the fork seal, I would change the fluid in both and see if that helps.

 

[FinalImpact]

A different thought:

If said repair left something out, the two forks may indeed be different. I'd opt for pulling them both and taking the tops off, dumping the oil, refresh both with the same weight and volume. Also compare the assembly stack confirming all the same spacers are present in the same order and neither of the springs are cracked/broken.

Its pretty easy, the fender is the only pain at all.

As Eric said, on some bikes; like MV Augusta, Brutale one fork is all about compression control while the other does only rebound control. Of course they are braced to take the added load and all that but for the most part, our fiz need only have the depth of the stanchion tube set equal as the damping is so weak you in both compression and rebound, I doubt anyone could tell the difference.

PS - It sounded like only one fork came apart. Hence the need to replace and measure the oil in both. << That was my thinking.. .. ..

 

[iSteve]

Like Eric said it should not matter if the preload is set different or the oil is different. You may have the forks twisted in the triple clamps or even tighten the axel incorrectly pinching the fork legs.

As a side note you can add washers under the fork caps to adjust the preload.

Here is a pic of a fork with spring in one leg damper in other.

 

[ReapeR]

i was looking at my bike today and was thinking, when i had that seal put in is when i bought my new clip ons, i had cbr clip ons on it before and it was lowered in the front but when i got the new ones i had to lower it more, so could that be it? im guna buy some oil and change both forks this weekend but could it be that is just too low in the front? it wobbles, and the front end feels very heavy, even when going slow it jus feels like it dont wana turn. dont know why i didnt think of that when i asked to start with.

 

[YZF73]

i was looking at my bike today and was thinking, when i had that seal put in is when i bought my new clip ons, i had cbr clip ons on it before and it was lowered in the front but when i got the new ones i had to lower it more, so could that be it? im guna buy some oil and change both forks this weekend but could it be that is just too low in the front? it wobbles, and the front end feels very heavy, even when going slow it jus feels like it dont wana turn. dont know why i didnt think of that when i asked to start with.

From what has been mentioned previously I think you're along the right lines with oil height likely being the problem, considering only one fork has been serviced. It is important that the oil height in the forks is equal, otherwise you may experience symptoms like those you've mentioned.

When you replace the fork oil make sure you do so by height, rather than quantity. You would be surprised how far off the height can be if you do it by quantity alone. Bear in mind that it's the height that effects the forks function, not the quantity.

Also, remember that the height is measured from the top of the chrome tube, with the fork completely collapsed (to mechanical bottom, be sure you reach this as the FZ6 has quite a stiff hydraulic bottom out even when the fork is empty), with all the internals removed (preload spacer, washer and spring). I find it best to get the help of a friend to hold the fork as upright as possible, then myself measure the oil height with a rule.


Hope this helps,

Yamahaboyz

Edit: From re-reading you're post above it seems that you may have pushed the forks up through the triple clamps, if so how far have you gone? This can well cause instability if taken too far. I run mine around 8mm through after replacing my fork internals to maintain the steering geometry.

 

[iSteve]

By lowering the front end you change the geometry of the bike and shift the weight balance slightly more to the front end. This will definitely make the front end feel heavy and less stable. But it also make it turn in quicker.

 

[FinalImpact]

By lowering the front end you change the geometry of the bike and shift the weight balance slightly more to the front end. This will definitely make the front end feel heavy and less stable. But it also make it turn in quicker.

I was gonna say lowering the tubes in the triple will make it turn in easier. Tire pressure, tire type, tire wear, all impact turn in. Wobble is more of set up and if you hit 80mph and don't feel comfortable, id start by a simple check list as oil level difference from fork to fork seems unlikely to make a difference on these.

Assuming mechanically all is well, oil levels matched, ride height for you is good, these would be reasonable steps.

Set stanchion tube depth No more than 10mm matched side to side
Set Tire pressure
Get your sag measured front and rear

Test drive and report back. Can you tell what all was done to the bike suspension wise and what tires are on and pressures??

 

[iSteve]

I don't think oil amount makes much difference until you get to the bottom of the travel. Also he only changed a fork seal so tire type, wear and pressure should be the same.

With the fork being lowered the amount of rake is less, less rake (camber) and the front starts to act like a shopping cart wheel with greater turning radius but unstable. Likewise a chopper doesn't turn well but is very stable.

Lowering the front end by raising fork in triple clamp can be compensated by adding preload. But then you loose some stability on bumps. A easier solution may be to lower the rear to match the front. This will make it feel more like stock but may bottom out before the full travel is reached.

For every action there is a reaction

 

[YZF73]

I was gonna say lowering the tubes in the triple will make it turn in easier. Tire pressure, tire type, tire wear, all impact turn in. Wobble is more of set up and if you hit 80mph and don't feel comfortable, id start by a simple check list as oil level difference from fork to fork seems unlikely to make a difference on these.

Assuming mechanically all is well, oil levels matched, ride height for you is good, these would be reasonable steps.

Set stanchion tube depth No more than 10mm matched side to side
Set Tire pressure
Get your sag measured front and rear

Test drive and report back. Can you tell what all was done to the bike suspension wise and what tires are on and pressures??

Raising the forks up through the clamps can cause instability, normally in the form of headshake under acceleration. Absolutely make sure that the forks are an equal amount through the clamps, otherwise the bike could well feel unstable generally.

Back to oil level, an unequal level can cause instability, unlikely to be evident at high speeds though, more so at lower speeds and whilst braking. However, considering only one fork has been serviced, are we even sure that the same oil was used as is currently within the unserviced fork? Even if the same weight was used this is still likely to cause issues, as not all manufacturers weights tally. Again it's well worth replacing the oil in both forks and ensuring that the heights are correct.

I don't think oil amount makes much difference until you get to the bottom of the travel. Also he only changed a fork seal so tire type, wear and pressure should be the same.

With the fork being lowered the amount of rake is less, less rake (camber) and the front starts to act like a shopping cart wheel with greater turning radius but unstable. Likewise a chopper doesn't turn well but is very stable.

Lowering the front end by raising fork in triple clamp can be compensated by adding preload. But then you loose some stability on bumps. A easier solution may be to lower the rear to match the front. This will make it feel more like stock but may bottom out before the full travel is reached.

For every action there is a reaction

I agree partly with this, however the terms you've used are slightly confusing your explanation.

If the forks are pushed up through the clamps (more fork showing above the top clamp) the rake changes through the lowering of the front of the bike relative to the rear. This affects the mechanical trail, the distance at which the tyre contact patch trails the steering axis' intersection with the road surface. The larger the mechanical trail, the higher the self centring torque developed by the resistance of the tyre contact patch to rolling along the road surface. Lowering the front end effectively reduces the trail number, hence self centring torque, with raising the front increasing the number, and therefore the self centring torque.

Increasing ride height in the front to compensate for the fork position is not really advisable, ride height (sag) should be set to the correct value (35-40mm for street) to allow the suspension to work within its most compliant mid stroke. This also allows geometry to be best maintained when the fork is in operation.

Lowering the rear can be done to correct the mechanical trail, however this is not really recommended as, as you've mentioned, travel will be lost, plus the bikes 'flick-ability' will be reduced. Again the sag should be set to allow the suspension to work within its mid stroke (30-35mm for the rear on the street).


Yamahaboyz

 

[FinalImpact]

I don't think oil amount makes much difference until you get to the bottom of the travel. Also he only changed a fork seal so tire type, wear and pressure should be the same.

With the fork being lowered the amount of rake is less, less rake (CASTER) and the front starts to act like a shopping cart wheel with greater turning radius but unstable. Likewise a chopper doesn't turn well but is very stable.

Lowering the front end by raising fork in triple clamp can be compensated by adding preload. But then you loose some stability on bumps. A easier solution may be to lower the rear to match the front. This will make it feel more like stock but may bottom out before the full travel is reached.

For every action there is a reaction

Off hand I'd suspect the overall setup of the clip-ons has simply made it uncomfortable. Perhaps they are not true thus creating a feeling of listing??

Its not like the fizzer forks are super strong brace wise. So I don't see oil, a few mm of spring preload or anything but the stanchion tubes being off several mm from side to side as the CAUSE of bike listing as is his complaint. And he specifcially said he measured those setting them equal.

Rake is a function of caster not camber btw. Perhaps put the original clip-ons back on???

 

[FinalImpact]

FWIW: I have R6 forks with them pushed up through the triple 8mm. Of all the positions from flush to about 14mm, I found this to be the happy spot for my style.

The OEM forks sag so much - i.e. me at just over 200lbs with gear had 44+mm of sag. Its now at 31mm and 29 in the rear. For my style, i like it there!

 

[iSteve]

Yes, I know it should have been caster just like the wheels on a cart but I wrote that at 6:30 am I may have been still sleeping.

 

[deeptekkie]

Yes, I know it should have been caster just like the wheels on a cart but I wrote that at 6:30 am I may have been still sleeping.

I must have been asleep as well because that's the way I read it. : )

 

[ReapeR]

just got back to work and read all the replies, as soon as i get a chance ill measure and let yall know how far i went down, its more than 8mm i can tell u that now. ill get back soon.

 

[ReapeR]

ok its kinda hard to measure with the clip on on it, but its rite at 1 1/4'', the clip ons are 1 1/2''.