Here's a post about the bike figuring in my avatar.

Riding bikes for 30 years, most of them were BMW GS or K (some of them were blue with sirens...)
I love the abilities of the GS to ride either on or off road, and love the confort and reliability of the K.
So I've been wondering why BMW never  made a K75 or K100GS, that would be a perfect long range trail bike.
It appears that apart some prototypes made for the Paris Dakar or bitzas made by some creative owners, this project never was made by BMW. So I decided to create it the way BMW should have done it. That means only with BMW parts.
And guess what? It's an easy job.Long but easy.

The donor bike is a 1985 K75C. Basic, with aprox. 100 000 kms, but in good genuine condition. I hade chosen this model because it has a drum rear brake, so easier to fit a R100GS spoke wheel instead of the disc brake later K75.
Why a K75 and not a K100? Because I want a 21 inch front wheel and I may have not room enough at the front engine with a 4 cylinder.
I ran a few months with the K75 in its genuine condition to spot defects, then a friend of mine borrowed it...and crashed. So the paint job was financed and I could start the modification.
The rear first: gear box paralever and final drive come from a K1100LT. I had chosen this instead of the monolever to avoid issues due to the higher suspension. With 2 ball joint articulations, the paralever is more tolerant to a wider angle.
At first, I wanted to fit a R100GS final drive on the paralever with K1100 driveshaft. Bit if it fits easily the swinging arm, the bevel shaft is different and has no circlip on the GS. I would have to open it, shorten the shaft and create room for the circlip. So I keep the K11 bevel, to see...

This option led me to adapt a rear disc brake and a R1100GS rim. Yet the caliper is different on R11 and K11, and I had to mill a bit its support to fit to the bevel case. Another issue is that the rear shocks is moved apart from the case, because there's not enough room for it besides the R11 caliper. A longer stud and washers solves it. I used the K11 genuine shock, longer travel and very soft but facing the big compressions easily.
I also had to mount a K11 footrest support, to fit the with of the paralever pivots.

The front, now.
The fork, the wheel, the bar come from a R100GS. Easy to fit, nothing special, the bearings are the same. I supressed the genuine useless direction damper.
I modified a right fork stanchion to fit it to the left and allow to have a second caliper. (Drill larger for the wheel axle, grind to adjust the caliper fixings and to give room for the disc rivets).
I kept the twin discs from the K75, narrowed them to fit the GS hub, bolt on, and made two new brake lines.



The front light and cockpit come from a R80G/S.
I cut the high part to put the original K75 instruments, on gum absorbers to prevent vibrations from destroying it. It works but the angle is not very efficient, I'll have to re adapt this.

This was looking weird. Looks like the Franco's spanish guards...

So a white GS windshield hides this fascist looking of the cockpit...

Then, with long travel suspensions, I had to lower the stands to fit the extra height of the biks. Longer studs and spacers, and it remains easy to put on stand and well balanced.


I also kept the exhaust system. I don't intend to fall, nor to cross rivers, and it allows to use the genuine panniers, so...Maybe I'll adapt a R100GS higher silencer later.

Then a new foam and seat cover, two knee pads painted in blues to evoque the genuine R80G/S color scheme, home made logos with the genuine police K75 GS and...that's it.


After a few rides, and 2 months searching for a bloody problem of pressure (the 2 inches long line that leads to the fuel filter into the tank was cracked! No way to see it, can't be detected when measuring pressure beacause the pressure drop is progressive, what a mess! I eventually found it because I inspected the inside of the tank, engine running at high RPM, and saw swirls at the surface...) it's a great trail bike.
First, on road, the extra wheel base due to the long fork and the paralever gives a grat stabilité to the bike. In spite of the Metzeler Karoo tyres, it handles very easily and there's grip on tar. The confort is excellent, better than on my K1100! Yet, the gear ratio is a bit long, but that's not a problem on road, and an advantage on highway.
Then, off road, the smooth suspensions are perfect for motricity. Anyway, they're designed to support bikes with a bigger weight and they'll cope with bumps or holes easily.
There's enought travel at the rear for casual tracks, and if it's too rocky, ride gentle and it wil pass.
I had some rides in the Alps, and never noticed defects for this use, but maybe this long ratio that sometimes makes delicate the ride in verry narrow pins. Well it's a trail bike, not a trial, and still easier than a R1200GS adventure...



The gummy footrests are not adapted to off road use, they're unprecise and should be changed for alloy spike footrests.
I'm considering converting it in a solo seat, with a long luggage rack.

Next ride, the Stella Alpina Rally in Italy, 2nd week end of July.

That is a very nice conversion!

I especially like the high front mudguard and that you did not use one of those foolish "bird beaks" that BMW insists on putting on the GS bikes.

Love it! Thanks for posting those details JBT.

I'm always very interested in looking at customised K75 bikes.

Cheers

Now that is just too cool.  I love it!

Rick G didn't you do something like this a while back??

jbt, I put a single seat and rack on my K75 inspired by my R80G/S PD.

Here's a photo which might interest you.


The build thread is here.

club_c wrote:Rick G didn't you do something like this a while back??

It's been shelved due to more important things and expense of engineering reports to get it on the road as I wanted it.
It probably will see light of day as time permits.

Great series of posts JBT quite enjoyable. Non rubber foot pegs yes amazing what comes back when the road turns to a track.

Rick G:  The K75 mono would be unable to match the R80 Mono due to the engine not being turned up at the front. All the GS or even some of the St bikes had a nose up in the frame engine gearbox setup. How on earth would we do that to the K series to exact a similar amount of travel???????

I laid the shock over to 54° to match the R80RT. Part of the reason for an engineering report, at $500 for each mod it was getting a bit expensive.

Gaz wrote:jbt, I put a single seat and rack on my K75 inspired by my R80G/S PD.

Nice job, but I'll prefer a flat rack, I often carry large boxes.
By the way, I was searching yesterday a seat tail for a friend and was amazed by the weight of this part. More than 5 kg including the tail light and turn signals.
I think I could make the K75 lighter also.

I think that's lovely.
Please let me know when you are bored of it and I'll take care of it for you.
Nothing like hope...

Thanks KMiles,
I think that I won't get rid soon of this K75, but if you're searching one, I saw a K75GS for sale in Germany: https://www.ebay-kleinanzeigen.de/s-anzeige/k-75-gs-enduro/652832160-305-7413
I can build another one if you prefer...

I eventually found a pair of Fehling crash bars, jus fitted them in order to go to the Stella Alpina Rally this week-end. I'll reinforce them to fit a protection plate for the water pump and the sump cover.

OOh, thats nice too...
Thanks for the link.

So many fine bikes, so little time...

A little update about my K75GS.
I adapted a protection plate from a R80G/S on the sump cover. No big deal to fix it. It won't resist much if the bike stands on a rock, but I'm not planning to try it. And it will do the job about rocks jumping from the front wheel.
I'm thinking about another plate in front of the water pump.

( I know...oil is leaking from the crankcase cover. Not my fault...I lended it to a friend who crashed and changed the cover by himself).
I eventually found Fehling crash bars. Not available anymore and quite rare in France, but I managed to get a used pair. Some scratches on the chrome, so I sandblasted it and painted it in black, so they match the frame tubes. 
They seem much more solid than the BMW ones and their gummy mountings.
Later, I'll probably add a bolt-on front jonction between the two crash bars to support the plate dedicated to the water pump.

I also converted R80G/S old footrests to the K75. It required a lot of moulding and grinding to change the position of the axle and to strenghten them, but it's much better than the genuine ones.


Yet the angle of the footrest is not perfect. They're horizontal, that's OK, but they're not perpendicular to the bike. Nothing really disturbing as they're wide enough to provide a good support.

Definately

That 21" wheel and high mudguard are so sweet looking.  If I was to mod a K75, yours is the model I would follow.  In my few remaining years I would love to do a trip to Alaska, and that is the bike I would want to use.

Spring, at least!


Mountain passes are re-opening. Nice scenary on the Mont Blanc, from 3300 meters below...

Fabulous looking bike and what a view

Make sure you submit this one for the calendar!  I want a version of that bike more than ever now.  You are happy with all the tire, suspension and various modification choices that you made?

Well...yes! It's a very pleasant bike to ride, on and off road.
The transmission ratio is a bit too long off road, I should change it for a R100GS or even a R80GS bevel drive, but the shaft needs machining to match the paralever shaft. In an other hand, the RPM is very low on highways.
The main problem is the lenght of the bike and the fork that can't steer as much as I'd like to, because of the reduced offset of the GS triple tree (compensed by the wheel axis offset). The fork tube is touching the front of the tank too early. Not a real problem, I just need to notice it when I change from my R100GS, the manoeuvrability is different.
I could grind a few millimeters the tank rib to save space.

That's awesome.  Last fall a road was completed from Inuvik to Tuktoyaktuk on the Arctic Ocean here in Canada.  This is now my great motorcycle quest to ride to Tuk and I've been thinking a suitably outfitted K75GS would be the perfect bike for this.  That's about 7000 km one way for me so long distance comfort and reliability has to be really good.

Cheers, Andrew

A little imrove of my K75GS: the OEM K1100LT shock was perfect for it, but I noticed that it was sometimes not stiff enough on big potholes when the bike was fully equiped. So I bought a used Ohlins shock for a K1, intending to fit it on the K75GS.

Two problems appeared:
- the soft line to the compression setting cracked and leaked. So the shock was rebuilt at a specialist nearby, and I got the spring resprayed.

- there's not enough room between the bottom of the shock and the brake caliper.
I thought it was easily solved by rotating the drive cover. But the holes are not symetrical, no position fits. The solution is to weld another fitting for moving the caliper back. I cut an old K100 cover to get the new fitting welded: 



The rear original fitting becomes the front fitting.


I asked many professional welders, but most of them refused to take the job as soon as they hear the magic word "brake": No, I won't take any responsability about brakes. Sad.
Eventually, I found a good welder who accepted. And made a very good weld. No finition required, nothing is too thick, it fits perfect.


I had to cut the breather that, now, is in the front of the caliper.

And my K75GS has now a beautiful and very efficient Ohlins shock.


The compression setting device is hidden behind the battery, protected but reachable.
The preload setting is just at the front of the shock.
I'm waiting for a new longer brake line before I can test it.

Amazing engineering, jbt
well done, congrats

Thank for the thread 
Great read

Thanks for your post! Good build
How was the Ohlins shock at the end? Better than the k1100 one?

Well, I stored the bike for the winter since I mounted the Ohlins without time to test it on road (or off road). 
Spring seems to be here now, as I'm rotating my batteries from winter bikes to summer bikes, I'll soon be able to test the new shock.

jbt wrote:Spring seems to be here now, . . .

Not quite here yet, but there's still plenty of transient delight to be had.

Yup
I can see that one little white flower over by the red door just ready to pop up!

Aaaah, spring...

Spring is sprung
The grass is riz
I wonder where the birdies iz.

Angry farmer wipes his eye
Says 'thank goodness
Cows don't fly'.




-Anon, but frequently incorrectly attributed to Spike Milligan.

jbt wrote:A little update about my K75GS.
I adapted a protection plate from a R80G/S on the sump cover. No big deal to fix it. It won't resist much if the bike stands on a rock, but I'm not planning to try it. And it will do the job about rocks jumping from the front wheel.
I'm thinking about another plate in front of the water pump.

( I know...oil is leaking from the crankcase cover. Not my fault...I lended it to a friend who crashed and changed the cover by himself).
I eventually found Fehling crash bars. Not available anymore and quite rare in France, but I managed to get a used pair. Some scratches on the chrome, so I sandblasted it and painted it in black, so they match the frame tubes. 
They seem much more solid than the BMW ones and their gummy mountings.
Later, I'll probably add a bolt-on front jonction between the two crash bars to support the plate dedicated to the water pump.

I also converted R80G/S old footrests to the K75. It required a lot of moulding and grinding to change the position of the axle and to strenghten them, but it's much better than the genuine ones.


Yet the angle of the footrest is not perfect. They're horizontal, that's OK, but they're not perpendicular to the bike. Nothing really disturbing as they're wide enough to provide a good support.

hello jbt, 
i just found this skid plate. what do you think about it?

https://www.caferacerwebshop.com/en/bmw-k75-k100-k1100-k1200-skid-plate.html

I will never get tired of looking at your bike.

@jbt and all the others
FYI

There's a guy in Germany named Gerhard - which would be 'Jerry' for english native speakers, I guess
I do know him from the forum Flyingbrick.de ( I do hope I a allowed to post that? )


he also converted a K75 to a K75GS and posted a clip a Youtube:
https://www.youtube.com/watch?v=4lPUswx_H1k

I like the hydraulic clutch mod!

Been thinking about doing something similar for a while. Someone on here mounted a hydraulic 'pull'-type lifter on the side of the frame and made a really neat job of it too. I have a similar type for my Guzzi 850-T3 California which lies along the gear box, but I'd like to try a Guzzi 850/1200 Stelvio lifter, if I can find one cheap enough to consign to the bin in the event of a complete failure.

Lorenzo17 wrote:[
hello jbt, 
i just found this skid plate. what do you think about it?

https://www.caferacerwebshop.com/en/bmw-k75-k100-k1100-k1200-skid-plate.html

Seems too thin to be useful.

Time for a new version of this K75GS.

As I'm know cursed to sleep with an air compressor to breathe, I can't rover without  finding a place to plug this device. And, of course, I have to carry it. It's not that big, but on a motorcycle, there's no extra room.
I 've been thinking for while about using an authority radio box, combined with a solo seat, to improve the carrying capacity of my bike.
I still have on a shelf these parts that were on my Comanche sidecar when I bought it.
So...let's do it.



Not so bad.

But I don't like the luggage rack, too close from me. I don't want to be disturbed when getting on or off the bike, it's high and I want to pass my left leg above the rear, not above the seat.
So no luggage rack here, I push it to the back of the box. The top case sits at the top of the box, it may seem loud but it's always empty when riding, I just use it to store helmet and vest at stops. It prohibits to use the small hatch of the radio box, so I had to find another way to unlock the full cover from outside, by using two wheel spokes to make pulls to operate the hooks.



Hmmm... not easy to operate, still need two hands to open...I will definitely supress these hooks instead, and by the same time the small hatch. I've bought a second radio box that will be used, this one being dedicated to test solutions.
The next step will be to install a Lifepo 24AH battery into the box, with a battery separator-coupler, to operate the breather during the night and to charge the battery during the day ride. A K1100LT alternator will be installed also to provide extra Amps.

The seat is given to my pal Jose to enhance it and give it colors!




Great and very comfortable. But...too high. My feet still touch the ground, but I don't like the position, too much bent on the hands. I can't move the bar upwards no more, and anyway I'm feeling too high when riding, I don't like it. So I called Jose and arrange another meeting to reduce the height...



I had to cut a piece of the two-seats tail to maintain the rear of the battery covers.  





I found in my stuff a 600 Tenere luggage rack. It fits perfect the low fittings of the K75 frame. I intend to fit it behind the tail to support a tent, so it will be to high and won't interfere when I step on the bike.



Then, time for a bit of electricity.

The fuel pump harness had bad wounds: the wires had became rigid, the coat is peeling...and I had some random power cut issues.


I had a spare harness from a Peugeot J5, that has the exact same connector but with a thicker layer around the wires. So I soldered it to the original wires.



Then, I added 2 small LED headlights to strenghen the OEM headlamp, a bit tarnished.



Good lighting, but the charging light on the dashboard is telling me that the K1100 alternator is not an option anymore.



What's next? Well...I was planning to ride to the Balkans with this bike but family issues made me change my plans. So I'm still here. I'm going to end the battery installation before testing this new function.

I'm a bit ashamed, also, to alterate the shape of this K75GS. I don't like it as this, in fact.

I have to make another one.

You have exactly the GS Brick that BMW should have made.

Thanks, il was the motto at the beginning...

I don't believe your charging light. A 50amp alternator is 700 watts (about 650 usable watts) - even with a second battery and heated clothes you should not be getting anywhere near that amount. You can work out your power consumption by adding everything up with the headlight on high beam. Do not count the horn, the indicators or the brake lights as these are classed as 'intermittant loads' and you should only be counting 'constant loads' (headlight, tail lights, ignition, clothes, heated grips, etc.). A good rule-of-thumb figure for a twin-cylinder motorcycle with points is 0.5 amps for the ignition system. If you allow as much as 2.0 amps (24 watts) for the K75, I think that is way over the top and is a good safe figure.

I guess that the English for your night-time breathing problem is 'sleep apnea'. It is not a pleasant problem to have.

Well, the charging light is glowing, indeed, when I use both the headlight and the led lights. But the alternator pick ups may be tired, I should check them.
I have the same problem on my K100, with the single headlight. So you may be right, I should not trust the charging light.
Anyway, I've ordered a Led headlight. I'll test it tonight, but it doesnt seem to be very efficient...


Yes, I'm suffering of sleep apnea. It's very insidious, I was sure that I was sleeping well until I had surgery and the anesthesist told me that I was scarcely breathing.
I had a sleep test for one night at the hospital, and discovered that I had an average 120 apneas per hour. The doctor told me I was only breathing 2 or 3 times per minute. And indeed, I realised that I had a very low breathing rate, even when awake. When riding, I'm usually breathing every 10 seconds.
The first morning after I slept with this pump was incredible: I was 20 years younger! Energy, resistance, a real miracle.
So yes, this pump is a inconvenience, but the benefits largely worth it!

What's new about this bitza?

Well, I rode a few days in the southern Alps to test the new configuration of this cherished and lovingly cared and meticulously maintained bike  and...I had many problems.  

Erratic lights, leaking fork, electrical loom failure and, to the end the death of the radiator fan, at the end of a warm day, with plenty of high passes to climb to reach home.
Never stayed stuck anywhere yet, but I had to ride 300km in mountain without passing under 70km/h to maintain enough airflow to cool the bike. Remember the movie Speed?

So...time for some corrections!
The fork was completely overhauled, with new stanchions and sliding bushes. Much more precise now...and no more leaks.
The light switch was autopsied and found out of order. A new one resolves the problem!
The fan motor was also dismantled and I found the guilty: a melted bush holder.
All the cooling circuit was carefully cleaned and checked.

The seat, too high was another time modified to lower it a bit.



I also modified the instruments cluster position: it was perpendicular to the fork, but not really facing me when riding. So I modified a K100LT instruments holder, with silent blocs, to adapt it to the light cockpit. And it solved this itching misalignment of the previous set.


Last but not least, I integrated the 2 lithium ion battery into the pizza box. An electronic coupler is managing the charge and allows to jump start the main battery if needed. I used a R80 battery holder with 2 straps, easy to remove and protecting by the same time the cable screws of any unnecessary contacts.
A cigar lighter plug allows to take power from the battery, and il can easily be taken off the bike in case of need to be used into a remote tent.


And there's enough room into the box to store the air pump and its accessories.


First road test: DAMN! The temp light is brighting red!   No, don't tell me it's a faulty head gasket!
No...I just forgot to plug in the brand new fan.  

So new test at dawn to seek some cool air on the plateau du Retord...it's OK!


Next stage: to install a Hepco & Becker tubular cases carrier, to fit heavy duty large aluminum cases on.

You have, without a doubt, the sweetest looking Brick I have ever seen.  Every detail is perfect.


Does it handle off road as nice as it looks?

Well, it's pretty good for off road. As well as a R100GS: I also have one so comparison is easy.
As long as you don't expect it to do what it's not designed for, you can cope with the dirt, smoothly.
The suspensions are good: I'm heavy but they never go to their bottom. The stand, yet, sometimes smashes the ground on (modest) jumps, but it's because the springs are too weak I think.
The biggest problem is the long final ratio that comes from a K1100LT: I wish sometimes I have a shorter 1st gear.
Maybe I'll try to transplant the OEM k75 bevel drive into the paralever case.
Another issue is the width of the tank at its junction with the seat, that is inconvenient to ride standing, the position is not very comfortable. But apart from smashing it with a hammer, there's nothing I can do.

lovely motorcycle you've got there, jbt
quelle moto adorable

all the best to you
salut

I'd swap it with your ecomobil anytime!


BTW, the friend of a friend is about buying one. I saw that you were having yours servicing: is it a challenge to find parts and qualified mechanics to service or repair it?

mon cher jbt, you can't compare your 75GS with an Eco.
Any Brick is a motorcycle, any Peraves is a vehicle. Worlds apart.

Well, as with every ageing machine, there are minor issues.

Mechanically, pretty everything is BMW.
Used parts are plenty and affordable.
All the manuals are available on quite a few forums
All the rubber parts of the intake system should be replaced every few years.
The battery has to be kept fully charged when not riding for more than a few weeks. It is essential for the correct function of the outrigger wheels.

Compared to a motorcycle, the Eco needs more and continuous TLC . You can't let it stand around for months without it.

There are two Achilles heels:

Nr 1:
All the electric connectors which ale plenty. These are ageing much faster than the mechanics.
Oxidated connectors are the enemy of every electric circuit. Game over.
That's why I stopped riding in winter season:
The salt on our roads just pushes the oxidation into a very, very fast forward.


Nr 2:
The 4+R gearbox built specifically for Peraves CH:
It is too weak and prone to mechnical defects with time.
A new one - if your are lucky to get one from Peraves CZ - is some 4'500 €.

After my gearbox failed, I decided to have it replaced with a used K1100RS five speed one for some 200 €.
These are said to last forever.
I have to do without the reverse now.
This is no big deal: It is in forward motion 99.8 % of the time anyway
As for parking, it's about the same as with a sidecar: Gearbox in N and pushing.
Hard, horizontal and flat ground is on your side.

An average mechanic with the necessary place, tools, good knowledge of automotive electrics and some common sense can easily maintain an Eco.

A lifting platform is a must because of the specific layout of any Peraves vehicle:
4 by 1.5 meters with a rail in the middle for the main riding gear, able to lift some 400kg to a height of 1.2 m.
Hoisting points in the front to strap it down, as it is tail-heavy w/o passengers.
You need 2 m open space above these 1.2 m which means a room of 3.5 m height.

BTW I think I remember somebody telling me that Ecos are not street legal in France?!

Nothing is street legal in France. But we are latin people.
Actually they never were imported here; One guy managed to register one monotracer.
But today it's possible to register it as a veteran, which allows it to be street legal.

I thought that Peraves CZ was out of business?