Teach me - fork oil

[tigersaw]

My Serow is over 20 years old. Slowly bimbling through checking everything.
Forks work and seem fine, but for a tenner its easy to replace the fork oil unless it lasts a lifetime?

What weight to choose - depandant on the rider weight, climate, stiffness required?
Type - Are all synthetic? Any brands to choose, Castrol, Rock oil, Silkolene etc?
Should it be a routine change, should it be combined with seals or not nescessary if they ok?

[fastdruid]

<deep breath>
Fork oil eh.

Firstly yes replace it. Fork oil is one of those things that slowly goes off, you wont notice it but you will notice the difference between old and fresh.

Secondly weight, lol. Weight isn't really the best of things to describe fork oil, its rather inconsistent and basically has issues.

Essentially though what you put in all depends on the type of fork you have, older forks (ie the serow) are pretty much going to be damper forks (rather like the SV) and take ATF rather than fork oil, this in itself has issues because ATF does not have a specified 'weight' but rather a range, admittedly a tight one, this means that different makes (and even batches) may have different 'weights', as a result you should make sure you use the same batch (ideally bottle) to fill them.

You may find this article helpful

http://pvdwiki.com/index.php?title=Suspension_Fluid

Unless the seals are leaking leave them be, ideally you should totally strip, inspect and rebuild but tbh just fresh oil will make a world of difference. Even if it has drain ports on the bottom you're still better off taking the forks off, removing the springs and pumping them to remove all oil, put some fresh fluid in, pump the leg a few times and then drain again, this should remove all the old oil. Then fill with fresh, pump multiple times until no bubbles then measure from the oil to the top of the tube with the spring removed and the fork fully compressed, that is you oil height, add or remove oil until you are at the recommended height, extend the fork, pop the springs in and measure again, that gives you a figure you can work with later to add/remove oil if you want to tune things without having to take springs out etc.

Druid

[tigersaw]

Thanks
I'm going to study what you have written and relate it to my bike.
I guess removing the spring is simply a case of undoing the cap and withdrawing it?
Pumping the fork, extracts the oil from the drain screw at the bottom or just tip it out?
Nothing will explode in a shower of springs and clips in the process?

Your link isnt bedtime reading lol.
The manual just states 10W fork oil - So I guess a 1L bottle of Silkolene will do the job?

Just found a youtube of it, well kind of. If only I read Japanese http://www.youtube.com/watch?v=tZJtrW39d1k

i have been thinking about doing this to the sv but wasent sure how to go about it :/

instead of making a new thread could some one answer a few questions

1. what weight oil should i get, i weigh in about 17stone (ish)
2.can i just syringe the oil out as i cant be botherd to drop the forks
3. how much oil should i use for each fork leg?
4. is it as simple as it sounds ? EG jack bike up remove fork caps pull springs and other bits and syringe oil stick springs back in and fill with corect amount of oil replace caps

thanks PS sorry for thread hijack

[fastdruid]

Originally Posted by barwel1992

2.can i just syringe the oil out as i cant be botherd to drop the forks

Well you can just syringe the oil out but you're not going to get rid of the crap in the bottom if you do that. Its better than nothing but no where near doing a proper job.

Druid

[fastdruid]

Originally Posted by tigersaw

Thanks
I'm going to study what you have written and relate it to my bike.
I guess removing the spring is simply a case of undoing the cap and withdrawing it?

On the serow I'm pretty sure yes, on bikes with adjuster screws in the top cap its a little trickier!

Pumping the fork, extracts the oil from the drain screw at the bottom or just tip it out?

Turn it upside down, and then pump it.

Nothing will explode in a shower of springs and clips in the process?

No

Your link isnt bedtime reading lol.

It *is*, should send you to sleep in about 20sec....

The manual just states 10W fork oil - So I guess a 1L bottle of Silkolene will do the job?

This is where weight is 'bad' (see that link), different manufacturers use different 'weight' scales. However on a serow I doubt it matters much.

Druid

[yorkie_chris]

Why ATF for damper rod forks? Just use whatever viscosity of fluid suits what you intend to do with them.

Also a thorough cleaning job on damper rod forks doesn't matter so much, not like there's a valve stack to get bits of crud caught in is there?

I just dump in a pint of paraffin and swish it about to get the worst of crap out.



Barwel don't be lazy, do job right. You need forks off to set oil height correctly.

So you can't get away with measuring the oil level with the bike on a front paddock stand suck the oil out with a pump and refill until at the same level as before?

[yorkie_chris]

No if you change height at all then you affect how it behaves on brakes. I'm just going through this with mine 'cos it's not using a load of travel on the brakes.

But I know I started with 125mm air gap, you don't know where you started, so what's point of doing something to "improve performance" if you are going to throw in another variable.

but if it's up on a paddock stand and held in situ then what can change.