BMW K bikes (Bricks)

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1Back to top Go down    Frame & Fairing Compatibility on Sun Jan 26, 2014 4:46 am

MikeP

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Spurred by a comment someone made about swapping bodywork, essentially turning a 16v K100RS into a K1 and knowing that there is a lot of "under the skin" differences between the two models, I thought I'd take a look at the compatibility of the frames.

Probably like many K-Series owners, I'd assumed that owing to the generic nature of the design and build of the K-Series (up to the 1200), mixing and matching between models would be a relatively simple task.

I knew that with the launch of the K1, the frame tubes were beefed-up (up to 32mm diameter from 30mm) and that the steering angle was steepened thereby changing the rake (27 deg) and trail (90mm).

The K100RS 16v was given the same, stronger frame but I can find nothing to confirm that the steering angle change was carried over, except that some specifications list the wheelbase as the same between two.

You'd think then that these two bikes would share the same part number for the frame but not so. It took me a little while to work out why:

The K1 doesn't have rubber inserts in the mounting points whereas the 16v RS does, plus, the K-RS 16v has the same swing-out lifting handle that has adorned all the K-Series from launch but the K1, owing to the bodywork covering the rearmost frame downtube, has a short horizontal tube that joins the downtubes above the gearbox mounting to assist lifting onto the main-stand instead.

The K1100LT shares the frame with the K-RS 16v but not the K1100RS. This surprised me at first but again it seems to be down to the lifting handle: The K1100LT has the 'traditional' one but the K1100RS has a fixed tube attached to the rear downtube running up to the rear frame (again a consequence of body panel arrangements).

The K100RS (8v) & RT/LT share the same frame but the K100C is different (I believe only inasmuch as the former have rubber inserts in the forward mounting points).

All the K75 models, C, S and RT share the same frame. Unlike the faired K100 models, the 75RT doesn't have rubber inserts in the forward mounting points (presumably because the triple is less prone to vibrations).

Swapping fairings etc looks therefore to be a much easier exercise for owners of the 8v K100 and K75 models (the K75 models have a slightly different fuel tank too except for the K75RT which uses the K100 tank).

Things are less simple for the 16v bikes and swapping some 16v bike panels over to 8v bikes is further complicated in the case of the LT by the fact that the whole fairing of the K1100LT was shifted forward by between 30 and 40mm (different sources quote different figures). This means that the support brackets are not compatible.

Of course, as some owners here have demonstrated, it is possible to swap the bodywork but it's not as straight-forward as the apparent similarities would make it appear. There are far more detail differences than I ever thought.


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1992 K1
1993 K1100R (used to be an LT)
    

2Back to top Go down    Re: Frame & Fairing Compatibility on Sun Jan 26, 2014 6:57 am

duck

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And then there's also the "missing" cylinder on the front of the K75 engine which further complicates matters as it changes the angle of the frame "downtubes" and radiator mounting.

Also, the K1100RS has a "Y" under the tank while all of the other Ks just have a single frame member.

I've never measured it but I'm pretty sure that the 4V bike frames also have a slightly wider rear section to deal with the added width of the paralever swing arm hump and stepped out backs of the peg plates.


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Current stable:
86 Custom K100 (K75C fairing, K75 Belly pan, Ceramic chromed engine covers, 32/10 final drive)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
93 K1100RS
94 K1100RS
93 K1100LT
91 K1
93 K75S
http://www.ClassicKBikes.com
    

3Back to top Go down    Re: Frame & Fairing Compatibility on Sun Jan 26, 2014 9:22 am

MikeP

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Apologies. I've just realised that I've posted this in the wrong section.


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1992 K1
1993 K1100R (used to be an LT)
    

4Back to top Go down    Re: Frame & Fairing Compatibility on Sun Jan 26, 2014 1:23 pm

SteveK1

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This is interesting information, not really available elsewhere. Thanks for posting.


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BMW K1 1990
BMW R60 /5 1973
BMW R100R 1992
Honda CB360T 1975
    

5Back to top Go down    Re: Frame & Fairing Compatibility on Sun Jan 26, 2014 8:23 pm

RicK G

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@duck wrote:And then there's also the "missing" cylinder on the front of the K75 engine which further complicates matters as it changes the angle of the frame "downtubes" and radiator mounting.

Also, the K1100RS has a "Y" under the tank while all of the other Ks just have a single frame member.

I've never measured it but I'm pretty sure that the 4V bike frames also have a slightly wider rear section to deal with the added width of the paralever swing arm hump and stepped out backs of the peg plates.
I am not 100% sure but didn't the LTs have that Y section after the big changes in late 1993. I seem to remember seeing a 94LT frame and thinking it was marked incorectly but found later that after late 93 all were the same.


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If everything seems under control then you aint goin fast enough:- Mario Andretti
Bikes 1986 K100RT, 1993 K1100 LT, 1994 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 & 1976 SR 500 Yamaha for now
    

6Back to top Go down    Re: Frame & Fairing Compatibility on Mon Jan 27, 2014 3:08 am

AL-58

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My '99 LT frame had the "Y" at the steering head. The shape under the tank was different to suit also.

Al


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'87 K100RS/HRD sidecar (1100 motor)sc25
'92 K100RS-16v (an ongoing renovation project, registered and on the road with original patina)

'87 K100RT with Paralever backend

"money cannot buy happiness, but it can buy another K and that's the same thing"

    

7Back to top Go down    Re: Frame & Fairing Compatibility on Wed Jan 29, 2014 4:39 am

Rabidchiwawa007

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Great info. On the same note, awhile back i owned a 1985 K100. Then i sold it after I bought my now 1992 K100 16v. Do the 16v bikes have a smaller frame overall? As I switched between the two, the 16v felt slightly smaller and my knees were a bit closer to the fairing. Also, there seemed to be a slight size difference when I set the two next to each other. The '85 just seemed a bit beefier.

Does this possibly have to do with different wheel / tire sizes among other things aside from frame?


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1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

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