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1Back to top Go down   K75 GS conversion Empty K75 GS conversion on Fri May 26, 2017 9:00 am

jbt

jbt
Silver member
Silver member
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.
K75 GS conversion K75c10
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...
K75 GS conversion K75gs_10
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.
K75 GS conversion 20150112
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.
K75 GS conversion 20150212


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.
K75 GS conversion Tdf_gs11
This was looking weird. Looks like the Franco's spanish guards...
K75 GS conversion Guardi10
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.

K75 GS conversion K75gs_10
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.
K75 GS conversion K75gs10

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...
K75 GS conversion 20160910
K75 GS conversion 20160912
K75 GS conversion 20160911
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.



Last edited by jbt on Fri May 26, 2017 10:45 am; edited 2 times in total

    

2Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Fri May 26, 2017 10:19 am

Point-Seven-five

Point-Seven-five
Life time member
Life time member
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.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

3Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Fri May 26, 2017 1:35 pm

Laitch

Laitch
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Life time member
@jbt wrote:
K75 GS conversion Tdf_gs11
This was looking weird. Looks like the Franco's spanish guards...
K75 GS conversion Guardi10
K75 GS conversion 44271


__________________________________________________
1995 K75 73,000 miles
K75 GS conversion Usa-lo10
    

4Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Sun May 28, 2017 3:04 am

Gaz

Gaz
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Life time member
Love it! Thanks for posting those details JBT.

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

Cheers


__________________________________________________
Gaz
1990 K75 6427509; 1987 R80G/S PD 6292136; 2010 G650GS ZW13381; 95 K1100LT 0232224
    

5Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Sun May 28, 2017 10:24 pm

Woodie

Woodie
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Life time member
Now that is just too cool.  I love it!


__________________________________________________
1985 K100RT
52667
"Keep your stick on the ice.  We're all in this together."  Red Green
    

6Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Mon May 29, 2017 12:40 am

club_c

club_c
Life time member
Life time member
Rick G didn't you do something like this a while back??


__________________________________________________
"There's never enough time to do it right, but there's always time to do it over."

1988 K100RS SE VIN 01477554
    

7Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Mon May 29, 2017 12:42 am

Gaz

Gaz
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Life time member
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.
K75 GS conversion Img_1720

The build thread is here.


__________________________________________________
Gaz
1990 K75 6427509; 1987 R80G/S PD 6292136; 2010 G650GS ZW13381; 95 K1100LT 0232224
    

8Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Mon May 29, 2017 1:00 am

RicK G

RicK G
VIP
VIP
@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.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

9Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Mon May 29, 2017 9:46 pm

K75cster

K75cster
Life time member
Life time member
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???????


__________________________________________________
Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

10Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Mon May 29, 2017 11:48 pm

RicK G

RicK G
VIP
VIP
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.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

11Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Tue May 30, 2017 1:45 am

jbt

jbt
Silver member
Silver member
@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.

    

12Back to top Go down   K75 GS conversion Empty Drooling on Sun Jul 02, 2017 5:24 pm

KMiles

KMiles
active member
active member
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...

    

13Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Mon Jul 03, 2017 3:31 am

jbt

jbt
Silver member
Silver member
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.

    

14Back to top Go down   K75 GS conversion Empty K75GS for sale on Mon Jul 03, 2017 8:47 am

KMiles

KMiles
active member
active member
OOh, thats nice too...
Thanks for the link.

So many fine bikes, so little time...

    

15Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Sun Sep 17, 2017 3:32 pm

jbt

jbt
Silver member
Silver member
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.
K75 GS conversion 20170711
( 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.K75 GS conversion K75gs_10
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.
K75 GS conversion 20170712

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.



Last edited by jbt on Sun Sep 17, 2017 4:16 pm; edited 1 time in total

    

16Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Sun Sep 17, 2017 3:59 pm

charlie99

charlie99
VIP
VIP
K75 GS conversion 112350


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OK75 GS conversion Au-log10

"redframe" rs "bitsa"  with many contributions from the k100 community ,,with many thanks
    

17Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Sun Sep 17, 2017 5:27 pm

Dai

Dai
Life time member
Life time member
Definately K75 GS conversion 112350


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

18Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Sun Sep 17, 2017 8:12 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
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.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

19Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Wed Apr 25, 2018 5:07 am

jbt

jbt
Silver member
Silver member
Spring, at least!
K75 GS conversion Img_5710

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

    

20Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Wed Apr 25, 2018 5:40 am

DeRodster

DeRodster
Life time member
Life time member
Fabulous looking bike and what a view


__________________________________________________
1992 K1100LT 6455194
1943 BSA WM20
1979 Yamaha DT-175
1974 Triumph 3TA / 5TA
1974 Honda 100
1969 Honda 50
    

21Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Wed Apr 25, 2018 7:44 am

Woodie

Woodie
Life time member
Life time member
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?


__________________________________________________
1985 K100RT
52667
"Keep your stick on the ice.  We're all in this together."  Red Green
    

22Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Wed Apr 25, 2018 9:30 am

jbt

jbt
Silver member
Silver member
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.

    

23Back to top Go down   K75 GS conversion Empty Re: K75 GS conversion on Wed Apr 25, 2018 7:52 pm

Woodie

Woodie
Life time member
Life time member
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


__________________________________________________
1985 K100RT
52667
"Keep your stick on the ice.  We're all in this together."  Red Green
    

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