lowering my K75, front forks

[jagarra]

Still working on getting my K75 comfortable when I stop.  I did install the lower seat option and that made a huge difference.  I just picked up a new Progressive shock with a 13 1/4" eye to eye length, is there a recommended distance one has to lower the front forks.  I made a rough measurement of the gap before it hits the handlebars and I figure I have about .400" to play with. 
Since I am asking about front forks. the PO installed Racetec emulators and maybe springs in bike, (feels kind of stiff), does anyone know the recommended fork weight and CC.

[The Mighty Gryphon]

In my experience you can lower the front about 10mm which is about 0.400".

I have Race Tech emulators and springs in my forks.  They really make the front end feel good and stable in turns without the harshness on expansion joints.  I don't recall what they specify for oil, I use regular old ATF in mine.  If you go to the Race Tech site you will find the filling instructions.  They don't specify a volume of oil but rather say to fill to a level.  I may be wrong, but iI think the level for my Showa forks was 6" from the top of the tube.

https://www.racetech.com/page/title/IP%20FEGV%20STD%20Emulator

[The Mighty Gryphon]

I put the emulators in a couple years ago after spending some scary days riding in the Rockies.

Downhill was bad with the severe brake dive the old forks had.  Going into a blind turn and then needing to scrub off some speed was not my idea of having fun.  The emulators and the single rate springs fixed all that, and as a bonus the harsh stiffness on rough pavement was greatly reduced.  They were some of the best dollars I put into my K75RT.

[The Mighty Gryphon]

I just checked their site.  For a 1987 K75S the oil level is 140mm from the top of the fork tube.  The amount of oil needed should be about the same or a little less than specified in the owner's manual.

The way I filled mine was to dump in enough oil to get a little above the correct level.  Then I stuck a tube that extended the correct distance into the fork and sucked out the excess oil.

[frankenduck]

You can get another 1/4" if you buy tires with an 80 aspect ratio next time.

[jagarra]

Thanks for all the replies, guys.  Looking at clearance issues it seems the best way to change fork oil is to remove each tube and deal with it that way.
 I am still looking for some guidance on the amount one raises the tubes when a lower rear shock is used, based the fairing I have on bike (Shoei) and its mounts plus bar position there is limited travel (.40") upward short of using bar backs to allow a higher positioning.

[The Mighty Gryphon]

That is correct.  The bars are the limiting factor on lowering the front. 

An alternative method to fill the forks would be to put in measured amounts of fluid in small increments and checking the level after each addition.  By adding up the amounts you put in you will have an idea of what it takes to fill.  Then you'll know for the next fork oil change.

The first addition should probably be about 3/4 of the amount listed in the owner's manual.  Then go in 10cc increments.  If I recall, my Showa forks took just a little less than the amount in the manual.

[jagarra]

Clearance issues require me to pull handlebars out of the way, will look at removing pad control panel and see what I can do to get clearance to access caps.  When I first got bike had to adjust legs to get axle to slide in smoothly, so being even on top did not equate to alignment at the bottom.  I do like the idea of making a 140mm pick up tube with a syringe on it to pull fluid down to correct level.  Figure I could make a plate to lay on top with a hole to create a stop for syringe and cut a tube to length so that 140 mm would protrude would under the plate.   

[frankenduck]

What's the Shoei fairing look like? Got any pics?

[jagarra]

The only picture I have is from the ad from which I purchased it from.  Tried to come in from top to change fluid, no go plastic caps too hard to get off.  Ended up pulling tubes and clamping in vise so I could drain and refill, way easier.  Looks like top retaining nut spins, do you have to hold cap bolt from end of slider to get retaining nut off, the top filler screw was no problem.  I have since the picture, put the correct Y spoke wheel on the front, plus new tires and pads and rotors. 

[Laitch]

Looks like top retaining nut spins, do you have to hold cap bolt from end of slider to get retaining nut off,

BMW calls that retaining nut the spring retainer (#5 in the attached drawing from MaxBMW's fiche). It doesn't unscrew; it's held in position by spring tension beneath it pushing it against a snap ring fitted into a groove above it. To remove the retainer, push down on it then remove the snap ring from the groove using a small screwdriver. Some here have used a gear puller anchored on the fork brace to push down on it.

There is a BMW K100/K75 service manual on this site that you can download to help you.

[johnny]

greetings...

its not complicated...

raked front end... how low you wantts to go...

j o

[Laitch]

raked front end... how low you wantts to go...j o

If you go too low, coffee from the cup in the cupholder could splash onto the instrument cluster during hard braking and possibly de-calibrate both the speedo and the tach making it appear that you are moving faster than you actually are, when you are moving, that is.

[frankenduck]

Why do you want to get the retainer thingy off? If you're just draining/refilling there is no need to remove that - only the filler plug.

Add fork fluid SLOWLY as it takes a while to seep in.

An 87 probably has the early forks - 330 CC per side.

A kitchen syringe is handy for filling forks:

[jagarra]

Thanks for clarifying how to get that retaining plug out.  The specs for the S calls out filling it to 270-290 ml of oil.  Standard 320-330 or so.  I ended up filling them with 280ml of 7 wt fork oil, in the process of putting everything back together now.  Will finish up tomorrow and install shorter rear shock and give her a test run.

[frankenduck]

S forks have nothing to do with the model designation. They were used in many later model K75 standards, S's and RT's.

It's very easy to identify the early forks vs. S forks.

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/k75forkoil/k75forkoil.htm

[jagarra]

Wow, thanks.  Luckily, I just set the tubes back into place and have them secured with only the lower bolt.  Can pull and adjust them pretty easily in the AM. 

I had to contact RaceTech via email as their 140mm measurement just didn't add up.  even when I added 330ml of fluid in one of the tubes it was still 200mm from top, don't know how they came up with that 140mm on their web page.   

[Laitch]

I had to contact RaceTech via email as their 140mm measurement just didn't add up.  even when I added 330ml of fluid in one of the tubes it was still 200mm from top, don't know how they came up with that 140mm on their web page.   

To verify, you've installed RaceTech emulators and you are follow the attached instructions to fill your fork tubes?

[jagarra]

Thanks that makes sense now.  but I am not pulling springs, I will just fill with prescribed amount from manual.

[Laitch]

Thanks that makes sense now.  but I am not pulling springs, I will just fill with prescribed amount from manual.

Are you installing emulators?  Which style of fork are you modifying?  It's still unclear to me what you're doing. 

[The Mighty Gryphon]

I would suggest that you slow down and make very sure of what you have and what you're doing.  A little extra time and attention to detail now will assuredly prevent pain and additional effort in the future.

Take one of your fork legs off the bike and remove the cap.  Dump all the oil that is in it into something that can measure how much was there. 

Remove the spring.  Is it straight wound or progressive wound?  The OEM spring is progressive wound and the Race Tech spring is straight wound.  Turn the leg upside down, the emulator should fall out if there is one.

Now is a very good time to clean out 35 years of shit that has gotten in the leg.  Get some kerosene and dump 5-6 ounces in the leg and work it up and down slowly a couple times and dump it out.  Repeat until it comes out clean.  Let the leg sit for 10-15 minutes upside down to allow all the kerosene to drain out.  If it was my bike I would completely disassemble the leg.  The emulator needs additional holes drilled in the bottom of the internals and I would make sure that whoever installed the emulator actually drilled them.  There needs to be no resistance to oil flow at the bottom of the leg for the emulators to work properly.  You mentioned stiff action, that could be the cause.

Once you've checked all the internals, put the leg back together with emulator back in along with any spring spacers.  Download the Race Tech instructions and follow them. 

With the leg still off the bike follow the instructions for filling with fork oil.  Carefully record how much you put in.   This is how much you will use the next time you replace the fork oil.  I recommend that you change the fork oil every two years.  I also recommend using ATF.  It is similar in viscosity, is more temperature stable with regard to viscosity, and has additives that help keep seals soft.

[jagarra]

Dumping oil was done yesterday, forks flushed out with some fork oil and blown out with air pressure.  forks filled with prescribed capacity of 7 wt fork oil. forks reassembled, Progressive shorter shock installed and test ride provided a better ride and feel than with the Ikon rear shock, in fact I really disliked the overall ride with the way the suspension was set when I got bike.  Ride was pretty harsh, not very compliant.  I am happy with how bike now feels, now to ride a mountain pass to see how it goes in the corners at speed. Side stand still works proving a good  lean, I can still get bike on center stand without using a board under rear tire, so that part OK, no shorting required.

I didn't pull springs because I am still working out a way to hold the cap down while removing the clip.  Was thinking of using press with a threaded long 8mm rod screwed in the cap where the filled plug was and use the ram to push it down.  Maybe next time I have them off.

[frankenduck]

You can use a wheel puller with the fork in the upper tree.