I bought a pair of forks from eBay last year as I couldn't keep oil in the originals.
They are the correct diameter, 41.3mm, and have the cast bridge and two piece guard.
At first I thought they were nice and firm and improved the handling. But lately I'm finding them hard work and spend most of my time avoiding manhole covers and anything above a few mm in height.
When I arrived home today after doing a couple of hundred miles, I measured the amount of travel between the rubber cap and the high tide mark.
It was only 40mm!
Dug out my originals and just pushing one down was able to get 90mm travel. It's really starting to put me off covering too many miles. The fairing is jumping about so much, I'm concerned that it's going to break a mounting (again).
I recently changed the oil and put 10w in thinking the PO had put really heavy oil in. Made no difference.
There doesn't appear to be an 'S' stamped anywhere either.
Not sure where to go from here. Looks like I need to change the springs or take out a spacer(?).
Comments please before I break out the spanners and wallet.

It all points in direction "Sport fork", the "S" should be stamped beside the filler plug.

But you also did get all parts needed as a retrofit kit, and then have to make this "S"
beside the filler plug yourself.

Some aftermarket springs, Progressive-brand for one, are meant to be preloaded, and often are shorter than the originals, and come with a length of PVC which is cut to length for application. Some folk wrestle the entire piece in which often results in a too-stiff spring.

It's important to know what version of fork you have as there are several oil capacity specs between the various early K models. The K75 'S' forks which I retrofitted into my K100RS take just 280cc per leg and this level rides to 440cc for other bikes/models. Far too much oil in the space will also result in a harsh ride and often blown out fork seals as well. One of the members published a chart some time ago showing how much oil goes into each models front suspension...

One way to confirm......take one leg of the bike, turn it upside down...
remove the bottom screw (support the stanchion, if you put the slider in the vice).

The sport fork have a 8 X 70 mm screw (due to a 50 mm spacer inside)
a ordinary fork would have a 8 X 20 mm screw.

Have a new crush washer ready.

Hi John, many years ago I bought some progressive springs for my solo. They came with 2 spacers which I fitted, but they were far too stiff. I seem to remember that the spacers were something like 3 inches long. After a couple of spacer shortening sessions, I eventually got the forks working sensibly.
By taking the fork top fitting off, you should be able to see if there is a spacer in there, it goes on top of the spring.

If (and it's a big if) that's the problem, then it's easy to fix.
Good luck,
Paul.

The sport fork got two springs in each leg, and a spacer between.

Definitely no 'S' stamped on the fork cap so think I can rule out the Sport option for the time being.
The forks were manufactured in 86 and 87 and the markings look like BMW rather than Showa. That would seem to indicate from the table that duck provided, that the oil capacity should be 330 or 360cc depending on being from a K75 or K100. I have 360cc in them and not convinced that such a small difference would reduce the travel by so much. Have been wrong before though.
Starting to look like the over long spacer with new progressive springs is the favourite. I seem to remember that the PO of the forks had bought them for his 16v and they wouldn't fit. But he said that they had been sold to him as refurbished. New seals and springs perhaps? 
Time to have a closer look.
Advice on removing springs, please.
How do you get the top off and do the forks have to be removed first?

John, you can get at the springs without removing the fork legs.
To remove the top plug, push it downwards until you can get at the retaining circlip.

Paul.

A wheel/gear puller makes getting th aluminum fork caps off easier:

If you have a helper handy (Thankfully I have a bored Dad floating around) it's not too difficult with two people, one person shoves down on the cap (probably with a T-bar pressing an allen bit in the bolt) and the other can shove the stanchion upwards to stop the cap taking it down with it, and then pluck the clip out. The cap has to go about an inch below the top of the stanchion, really impossibly difficult by yourself unless you have a tool to help like duck says.

Hmmm. Think I qualify as the bored dad now.
That's a job for tomorrow evening. If it is the spacer, sounds like it could take an eye out if you aren't careful.

Rather than too long a spacer, I'd be thinking no spacer at all where one should have been fitted.  Perhaps a short owner may have done this to compensate?

You say there is only 40mm travel available.  If a spring is meant to have a spacer to get the correct travel, a longer spacer will give the forks more travel (and will not make the spring harder, just higher).  If someone chose to fit no spacer, there is less travel available).

Al

Get your point, Al. But that would mean that the bike would be nearer the ground and, unless my legs really are getting shorter, I would probably notice it.
Think surgery is the only answer. That's the bike, not my legs.

Comberjohn wrote:Definitely no 'S' stamped on the fork cap so think I can rule out the Sport option for the time being.
The forks were manufactured in 86 and 87 and the markings look like BMW rather than Showa. That would seem to indicate from the table that duck provided, that the oil capacity should be 330 or 360cc depending on being from a K75 or K100. I have 360cc in them and not convinced that such a small difference would reduce the travel by so much. Have been wrong before though.
Starting to look like the over long spacer with new progressive springs is the favourite. I seem to remember that the PO of the forks had bought them for his 16v and they wouldn't fit. But he said that they had been sold to him as refurbished. New seals and springs perhaps? 
Time to have a closer look.
Advice on removing springs, please.
How do you get the top off and do the forks have to be removed first?

30 ccs of fork oil can make a big difference. Because part of that volume is taken up by the spring itself.  I had a K100RS4V once that rode like a jackhammer on the freeway. I drained 10 ccs from each fork and that made it much better.

Jackhammer is a perfect description of it.
Do you really think dropping it to 330cc would make that much difference?
40mm or inch and a half movement is hard going on anything other than a really smooth road.
Back to the K golden rule. Try the simple(and cheap) fixes first.

That's what I'd try first. (It's really not the volume of fork oil that matters but the volume of air in the fork as air is much more compressible.)

Looks like duck hit the nail on the head.
I drained the forks this evening and pushed the bike forward with the front brakes applied. Using a cable tie around the fork tube I measured 140mm travel instead of 40mm.
So looks like the springs aren't to blame.
Question now is how much oil should I put in?
Definitely no 'S' stamped on them and don't think they are Showa. I'm guessing that they are BMW and from a K75 or K100.
Using duck's table, I think 330cc rather than the 360cc that I had used.
What does the panel think? Would that be the answer?
10 or 7.5w oil?

Hi there, as per my experience and the Haynes indications, 10 is too much for real, pothole infested, roads. I am using 5.
Best regards
JAP

I use Honda SS-8 (which is a 10W) in all of my Ks.

From what I've heard on fork oils, they are not standardized so 10W from one vendor may not be the same as 10W from another vendor. 

I'd go with 330 ccs.  Just add more later if the front dives or feels too soft.

And in my 'S' forks and because I'm not too heavy, I use 5W. It helps make them more supple over the ripply bumps. 10W works ok too.

7.5 is a good compromise for good roads ...have mixed 30 % with 10 weight ...not so good on pot holey roads  but liveable

past due for replacement in gerty

Comberjohn wrote:Looks like duck hit the nail on the head.
I drained the forks this evening and pushed the bike forward with the front brakes applied. Using a cable tie around the fork tube I measured 140mm travel instead of 40mm.
So looks like the springs aren't to blame.
Question now is how much oil should I put in?
Definitely no 'S' stamped on them and don't think they are Showa. I'm guessing that they are BMW and from a K75 or K100.
Using duck's table, I think 330cc rather than the 360cc that I had used.
What does the panel think? Would that be the answer?
10 or 7.5w oil?

Comberjohn,

Any update on your fork oil dilemma? Did you opt for 330ml/fork or did you go for a lighter weight oil....or a bit of both? How does the ride feel now?

Reason I ask....I changed my fork seals about 10 days ago (I'd noticed the left one was leaking) and refilled with fresh fork oil (Castrol 10W), filling each fork with exactly 360ml as per Ducks table and the Haynes manual etc for a K100LT. Since then, while it is satisfyingly leak tight, the ride has become very hard - your description of jack hammer and avoiding the slightest bumps (easier said than done) sums it up pretty well. This is a big change from how the bike felt before. 

Incidentally, when I replaced the fork seals, I removed the forks from the bike but did not dismantle them so I know that I have not disturbed the springs or inadvertently removed any spacers etc so I am certain it is either oil weight or oil level that has brought about the dramatic change.

I have just ordered up some Castrol 5W fork oil from Amazon but would be interested to hear your views before I go and change the oil again. Failing that I will take Ducks advice and start with 330ml/fork and see how that improves the ride comfort

Hi Paul. Sorry, should have updated the thread.
I replaced the oil with 330cc of Castrol Synthetic 10w and now the forks are fine. Just bought it in the local Halfords.
Wouldn't have believed 30cc would have made such a difference.

Hi Comberjohn,

Really appreciate the quick reply and your update. 

While I wait for the new oil to arrive (it was easier to get it from Amazon rather than my local Halfords - slightly cheaper and free postage too), I'll see if I can drain off some of the existing oil to reduce the volume by about 30ml. If that has the same effect as you have noticed, then I probably won't bother to change the current 10W oil yet.

Thanks for your help

Post "post" edit.... just successfully removed 30ml of oil from each fork - carefully removing fork drain plug at bottom of forks and used syringe to draw off the desired quantity of oil (had a handy unused 10ml syringe with a printer ink refill kit). Minimal mess too. I'll see what difference that makes on the ride to work tomorrow (kept the drawn off oil, just in case I need to squirt a bit back in again!)

Not to hijack a thread, but...

Anyone have experience/an opinion on these? Luftmeister anti dive kit

I haven't seen or heard anything about the Luftmeister anti dive but if they are the type that virtually locks the forks so there is no dive I would not recommend it to anybody.
The first time I came across that type was with the ST1100 Honda and it was absolutely woeful because while the brake was applied you had almost no front suspension.
I gather that over the years they have been reined and many of the manufacturers have abandoned them.
Luftmeister usually make good equipment so I wouldn't imagine they would be junk.

Works Performance out of CA makes dual rate spring kits that get good reviews from K bike owners as well as owners of other brands.

http://www.worksperformance.com/

I recently bought a set of Wilber's fork springs for my 1985 K100RS.  At 42 K miles I don't expect the installed springs are so tired, but the Wilbers were available at a good price and I bought them.  It's time to replace the fork oil, so I may install the Wilbers springs as well.  I've never been in these forks, so I consulted a part fiche and it appears the OEM springs should be single rate.  The Wilbers have tighter coils on one end, which I take to mean they are progressive wound.  
Should they be installed with the tighter coils in the bottom or the top of the forks?  Does it really matter?

Traditionally (in Japan at least) the tighter wound end goes at the bottom, but I can't imagine it matters as long as they're both the same.

If you put the tight end down it will slightly increase the fork oil level since there's a larger volume of spring at the bottom.

Progressive springs is usually mounted with the tight coils up to reduce unsprung weight.

It's important to remember, if the bike is in the southern or the northern hemisphere the eon flux of the borealis either neutralises the oil increase or decreases the unsprung weight.
:suspect:

Point well taken    Time to move on to matters of substantial import, to wit, wrapping my brain around the advice given in post #11 for removing the caps/springs...

Kyle10 wrote:Not to hijack a thread, but...
Anyone have experience/an opinion on these? Luftmeister anti dive kit

We used to (think we needed to) use those in our Airheads back in the '80s. They're simply a short coil spring and a bit of thicker fork oil. In the '70s-era fork legs all they did was limit the suspension travel causing the springs to smash the daylights out of the rubberised bushing at the bottom of the fork, leaving bits of atomised rubber to clog up the rudimentary damper rods. Walk away.

Two Wheels Better wrote:It's important to remember, if the bike is in the southern or the northern hemisphere the eon flux of the borealis either neutralises the oil increase or decreases the unsprung weight.
:suspect:

It's the Australis in the Southern Hemisphere so if you use the Eon flux oil then it will go highly negative so you need to use the A-Eon flux of the Australis which will keep it neutralized until you cross the Equator when the swirl will be in the opposite direction and it will go crazy with positiveness and the front will almost float causing understeer.

Fork spring epiphany: place one spring tight wind up and the other tight wind down. This balances the universe.

brickrider2 wrote:Point well taken    Time to move on to matters of substantial import, to wit, wrapping my brain around the advice given in post #11 for removing the caps/springs...

I'd do it by using post ten.