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.

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.

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

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

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.

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

Al

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?