Fork Strip-down

I've removed & stripped the front forks so I can have the fork lowers powder coated (the lacquer is starting to get a bit tatty & as I'm having the wheels done, I may as well get these done at the same time)  I'll replace the dust seals & oil seals - is there anything else it's worth replacing at the same time?  I'll measure the springs as well to check they're with tolerance.  Any recommendations on fork oil, or is it pretty much the same?

Cheers

One thing a lot of people do is to install progressive springs, its a recommended upgrade for many bikes as it improves handling and rideability. The progressive winding means that as the suspension becomes compressed the springs become stiffer. Its one of the things I am going to do with the GSX.

Andrew, excuse my ignorance, but how do progressives differ from standard.  When I took the springs out, I see that they're more tightly wound at the bottom than the top - I thought that's what progressives looked like - or are the standard springs like that but not progressive?

Do they look like these, if so they are progressive, I'm not sure if standard though.

I just downloaded the service manual for a VL800 (2001-04) and the photo shows progressive springs, so just ignore me

I'd just go with a slightly heavier oil to reduce the dive a little, other than that the vl forks give a pretty good ride with plenty of travel without bottoming out or being to harsh.

Andrew - at least you've just confirmed I'm not going mad !!

Sim - what grade would you say - I believe that standard is 10, the next one up is 15.  Reading around, the other school of thought is to stay on the same weight, but go for better quality eg. Silkolene.  

The manual says "The outer and inner tube’s slide metals must be replaced along with the oil seal and dust seal when assembling the front fork." - any thoughts ?  I was going to do the seals, but is the metal necessary?

And would you automatically replace with OEM stuff (seals, £15 a piece) or pattern (seals, £8.17 a pair).  I don't mind spending the money if I'm getting superior stuff, but is it all likely to be the same in a different packet?

Oil, Replace with 15w and if you find it to harsh? draw some out with a syringe and tube (say half) and top up with 10w, I'm only saying this because I always thought mine dived to much under breaking.

Me personally, I'd just replace the seals with OEM (you know they'll fit) and oil from the same manufacturer as each manufacturer is probably different.

ps.just in case your feeling flush 

http://www.ebay.co.uk/itm/Progressive-Fork-Springs-Ohlins-Suzuki-VL-800-C-800-Intruder-WVBM-2001-2004-/121099132203?hash=item1c32121d2b:g:LFcAAMXQJ3xRdP-H

However, when you consider that Suzuki original springs are £62 each, these are actually good value.  I'd always replace springs as a pair.  If mine need replacing, I know what I'll be going for

I've measured the springs today - they measure 550 mm, which is 10 mm over the service limit.  Kinda surprised me as I have less than 20k on the clock.  

Does anyone have any idea what the the standard length is   I've looked through the manual & can't find anything.  The Ohlins that Sim linked to say that they're 503 mm - 47 mm seems a helluv a lot of wear - almost 10%

I've no idea sorry?, I bet it'd be hard work getting that nut back on the top of the forks if the springs were much longer though 

I wonder if the Ohlins come with some sort of spacer with them only being 503mm?

Going to make a couple of calls tomorrow - they range in price from £66 for a pair of Wirth to about £100 for Ohlins.  In a quandary as to whether 10 mm is that critical - or as the forks are stripped down anyway, just to change 'em & save the hassle in a year or two

katsd wrote:

Going to make a couple of calls tomorrow - they range in price from £66 for a pair of Wirth to about £100 for Ohlins.  In a quandary as to whether 10 mm is that critical - or as the forks are stripped down anyway, just to change 'em & save the hassle in a year or two

Did you find any information Dave?

Contacted Suzukis (no) help (whatsoever) line - they're looking into it & are going to get back to me.  Easy enough for them to measure up a replacement off the shelf - I assume they still have them !!  I'm guessing it's going to be in the 540 region - if that's the case, I'm then going to contact an Ohlins stockist & ask about the difference in length - I'm guessing you're going to be right about the spacer.

katsd wrote:

  I'm guessing it's going to be in the 540 region 

Surely new springs would be longer than yours which measure 550, or am I missing something here?

Erm - good question.  I was working on the theory that a new spring is shorter & as it looses elasticity it become looser, therefore longer.  But do you mean that as they get more use, the coils compress & the overall length shortens ?

katsd wrote:

Erm - good question.  I was working on the theory that a new spring is shorter & as it looses elasticity it become looser, therefore longer.  But do you mean that as they get more use, the coils compress & the overall length shortens ?

Work on the opposite theory 

Doh - guess as soon as Szuzki get back to me, I'll know the answer.  On that basis, you've just saved me anywhere between £70 - £100 - cheers Sim

When (if) Suzuki get back to you on the new spring length? it'll probably only be a few mm at most, you can always use pvc pipe the same diameter as the spring to make spacers to regain the ride height, the spring rate won't have decreased over time, only the sag.

Yeh - I've read about using PVC pipe somewhere else.  I'll post as soon as I get an answer

This is an interesting read on springs if anyone has time to kill?

What is Spring Rate??
Spring rate is a measure of how stiff a spring is.  It describes how hard you have to push to make it move a given distance.  Spring rate units are Pounds / inch in the English system or Kg / mm in the metric system. So, if you rear shock spring is 280 pounds / inch (or 5.0 Kg / mm), you must compress it with a force of 280 pounds for it to become 1 inch shorter.  You would have to push it another 280 pounds to make it compress another inch.  Thus if you compress it a total of 560 pounds, it will compress 2 inches.
 
Do Spring Rates Ever Change??
No, Never.  Over time the spring may take a slight compression set (become shorter), but the rate will never change.  In fact when the spring makers wind a .44 Kg / inch spring for a 01 Suzuki or Kawasaki it is 470 mm long.  They can heat it and completely compress it for a set amount of time and it will "take a set" (shorten) by 10mm and become a Yamaha .44 Kg / mm by 460 mm spring.
 
What Do I Do If My Bike Sags More Than It Used Too??
Add Preload.  A highly stressed spring like our race bike springs will shorten slightly over time.  On your rear spring you simply turn the spring preload adjusting nuts to add preload.  On your front springs you would have to measure them and preload them with washers to make up for any slight compression set they have experienced.  (At Too Tech we always measure the front spring length before installing them back in the Forks.)
 
Do Suspension Springs Wear Out or Why Do Springs Break??
In our Motorcycle world springs rarely break.  A well designed steel spring will basically last forever.  How long a spring lasts is based on how much stress is produced in the wire when it is compressed to it's minimum length AND how many cycles (times) it will experience this load.  Engineers have charts to describe how many millions of cycles a given spring material can take at a different levels of stress before they fail. (See chart below) As the stress in the wire increases, the number of cycles until failure decreases.  The larger the spring wire diameter is, the less stress the wire will experience for a given spring rate.  Motorcycle suspension springs use relatively large diameter wire for the loads they see in service thus they seldom experience enough stress in the wire to cause breakage.  Some aftermarket companies try to use cheap wire which can't handle high stress levels without severely shortening their life expectancy.  But most of these companies have seen the error in their ways and now I am not aware of any companies with chronic spring breakage problems.
The chart below is used to predict how many cycles the spring can experience before it fails.  First we must determine which chart line to use.  This is determined by analyzing how the spring will be used.  The second picture down on the left side shows a spring cycling from no load to it's maximum load (or maximum negative stress).  Our springs have almost no load at full extension so the second picture best describes the stress pattern our springs will see (from 0 to max and back to 0).  This stress pattern is considered normal, so we use the standard graph marked "R=0".
The chart on the right is for some mild steel.  If it were a graph of spring wire it would look similar but the allowable stress loads would be higher. The X axis (horizontal axis) on the bottom denotes the number of cycles the spring will experience before it breaks while the y axis (vertical axis) describes how much stress the wire receives during each cycle.  If you follow any one of the lines you will notice that as the number of cycles increases, the allowable stress the spring wire can handle goes down.  Follow the "0" line.  Note that if we want to design for only 1000 cycles, our material could handle about 105,000 PSI stress in the material before it failed. If we want to design for 100,000 cycles, we can only stress the wire to 80,000 PSI.  Notice that at about 500,000 cycles the line levels out at a stress level of about 75,000 PSI.  This means that if we subject this material to a maximum stress of 75,000 PSI, it can be cycled indefinitely and never fail.  
If a steel spring is designed properly (utilizes the proper wire size) for a given application, the spring will never experience stress levels higher than the horizontal part of the line.  Thus a properly designed spring will last forever.    This is a unique property of steel only.  For instance aluminum, titanium, and other exotic materials continue to "age" regardless of their stress levels (there is no horizontal part of the line).  Because of this constant aging, engineers must use large cross sections to keep the stress levels in the material very low. As long as the stress levels are very low, these materials can last a very long time.  (Think about this as your aluminum bars get to be a few years old!!!)

 
Do I Change The Spring Rate When I Turn My Rear Spring Adjuster Nuts To Change My Preload??
No, only the preload is changed.  The spring rate remains the same.  Increasing the spring preload will raise the ride height, so the bike will be taller and ride higher in the stroke.  But it will not get stiffer any faster as you use up your travel.  For the shock to get stiffer as you use travel, you must change to a higher spring rate.
Why Does A Heavier Rider Need A Higher Spring Rate??
The bikes suspension is a combination of spring rates and damping rates.  It can be optimized for only one weight of rider and bike.  As the rider weight changes the spring will have to be changed to maintain the optimized combination. The relationship between the total weight of the bike and the rate of the spring determines the Natural Frequency of the system.  To maintain the same Natural Frequency ratio, if the rider gains weight, the spring rate would need to be increased. 
Natural frequency can be calculated or derived by measuring the static deflection of the bike when it is taken off the stand.  Measure the amount the front triple clamps move downward from full extension when the bike is removed from the stand and the rider stands on the foot pegs.  This sag, plus about 3/8" to account for fork spring preload, determines the SD or static deflection in the formula below.  Now put a heavier rider on the bike and measure the new static deflection and put it into the formula.  You will note that as the Static Deflection gets bigger, the Natural Frequency gets lower.
To maintain optimal suspension handling, you want the NF to remain the same so larger riders need stiffer spring rates.

NF = Natural Frequency in minutes (divide NF by 60 to get NF in cycles per second.
SD = Static Deflection of the machine (if the spring starts with no preload)

Yeh - I'd found that page as well - absolutely no idea what they're on about !

katsd wrote:

Yeh - I'd found that page as well - absolutely no idea what they're on about !

Hmmm, ok, I'm worried now! 

I'm quite simple-minded & suffer from information over-load. I'll give it another go tomorrow

Springs under compression get to the stage where they get coil bound & wont give you anymore ''spring'' movement where as springs under tension get weaker as they get stretched out & thereby get weaker.
The only way to get the original length & strength back is to have them heat treated by a proper spring maker or renovator who can get the spring to it's optimum power etc, only trouble is they will go lose or hard again but quicker as it's only a stop gap operation.
That's why it's cheaper to buy new springs to do the job.

Right - so in idiot terms - if the spring was being pulled apart, it'd get longer, whereas these are being pushed in, so they'll get shorted.

Soon as Suzuki can be arsed to get back to me - I'll know where I'm at

in my manual it says service limit 540mm ( 21.26in )

If you needed spacers to pre-load some tired springs these can be made from a range of materials - metal or hard Nylon type plastic tubing. Some bikes have spacers as standard & if around the right size can be used. I've even known of surplus car engine valve springs being used as 'spacers' (even thought they were compressible).
When I stripped my VX forks the other year the standard components were not present - & I think the springs were from a Bandit 1200 - these are longer than the standard VX springs & as that bike is a similar overall weight they seem to be a reasonable upgrade. It does take care & effort/force to re-assemble the spring caps though !

mally wrote:

in my manual it says service limit 540mm ( 21.26in )

Thanks Mally - what I really need to find out is what is the original length of them when new.  From what Sim has told me (in my ignorance) is that mine are still within the service limits.  Which leaves me with a dilemma - until I find out how much they have worn, I won't know whether to replace them - if they were 555 mm at the start, they've only shrunk by 5 mm - if they were 570 at the start, they've lost 20 mm & I'd sort it whilst they are stripped down.

If they are slightly worn, I'll probably go down the spacer route - if they're more than 50% worn, then I'll be replacing them with a pair of Ohlins or Wirth.  But until Suzuki get back to me, I'm stuck (mind you - the lowers are still at the powder coaters, so I can't do anything yet !!)

sorry miss understood i will try and find out

I had a great idea this morning    it was to measure the length from the bottom of the fork shroud to the bottom of the fork leg whilst holding the bike upright but not sat on it, then get someone with a newish Intruder to do the same (johnboss), thus giving a rough measurement on difference from new to old? before we all die waiting for Suzuki to reply     then I remembered your bikes in bits   No use whatsoever I know, Just show's my minds always working though 

I'll give it a go !!!!

katsd wrote:

I'll give it a go !!!!

A couple of hours and you'll have it back on the road 

Finally got an answer back from Suzuki - unfortunately, it was somewhat ambiguous.

"Dear Mr Reeder
 
Thank you for your recent telephone call regarding the Fork Spring original length.
 Having checked with our Technical department I can advised that the length was 540mm 21.26 inch`s.
 I trust this information has been useful to you and should you need any assistance in the future please do not hesitate to contact us on 0500 011 959 we would be happy to help you where possible."


So they basically told me the length that it states in the manual - not whether mine at 550 mm need replacing.


I went back to with 


"Thank you getting back to me.  Can I just clarify some please - as the manual quotes a service limit of 540 mm, does this mean that (as they are that length originally) there is absolutely no deviation from the original length allowed ie., they have to be changed as soon as their length differs from 540 mm.  Mine are 550 mm, so I assume this means that they have to be changed?  Sorry to be a pain about this, but it seems a bit strange that they have absolutely no tolerance from the original length.  Or am I misinterpreting the service instructions?"


The reply cam back


"Having liaised with our Technical Department and checking the Service Manual,  I can advise that the following,
 
Measure the fork spring free length.  If it is shorter than the service limit, replace it with a new one. 
Front fork spring free length service limit: 540mm (21.26in)"


So the springs compress with use - You were right Sim, I was wrong.  On the plus side, mine are still within service tolerances 

That's what I told you also Dave. A compression spring cannot grow longer unless someone has altered it or replaced it. Just put it back in & forget it.

So we're still none the wiser to the original length  

peardrop3 wrote:

That's what I told you also Dave. A compression spring cannot grow longer unless someone has altered it or replaced it. Just put it back in & forget it.

I know, I know - you managed to put Sims lecture into "easy for the idiot to understand language" for me

Sim - yeh, it's as if it's some kind of industrial secret.  Guess we'll never know unless someone has to buy a new spring at some point - or of a member with a brand new bike bike fancies stripping their front fork down to satisfy our curiosity (Johnboss?) !!!!

Sorry Dave, I'll go away now

peardrop3 wrote:

Sorry Dave, I'll go away now

Seriously mate, your way of explaining it made me understand

I try Dave! In fact Rosie says I'm very trying

peardrop3 wrote:

I try Dave! In fact Rosie says I'm very trying

Welcome to the club!!!