K75s and 2V K100s have a monolever final drive.
4V K bikes have a paralever final drive.
On a monolever bike, under acceleration, the push from the rear tire's contact patch causes the swing arm to rotate downwards. The contact patch moves slightly and the rear end of the bike is pushed up. This is commonly referred to as the "jacking effect." On a paralever bike there is a parallelogram formed by the swing arm and the strut to the transmission below it. This keeps the contact patch in the same place and the final drive does not rotate as it travels up and down. The result is elimination of the jacking effect and more consistent handling.
(In reality the geometry of the paralever setup isn't a perfect parallelogram and the paralever final drive does actually rotate a bit but nowhere near as much as a monolever final drive. I'm just explaining the basic concept here, not doing a detailed engineering analysis. For a more detailed description of the differences between the monolever and paralever systems you can read Anton Largiader's article on the topic
here.)
Converting From A Monolever To A Paralever Converting from a monolever to a paralever is a straightforward project. Here's what you'll need:
Paralever final drive
Paralever swing arm
Paralever strut
Paralever drive shaft (front and rear halves)
Longer shock compatible with the paralever system (like one from a 4V K)
Transmission from a 4V K bike (to support the front end of the paralever strut)
Since, aside from the strut mounting tangs, the transmission casings of the 2V and 4V Ks are identical, installing a 4V transmission on a K75 or K100 is bolt-on-n-go. (Some of the 2V transmissions have undrilled mounting tangs so drilling/machining those is also possible.)
The paralever swing arm has a bulge in it that will hit the rear of a right side K75 or K100 peg plate. You can deal with this by either shimming out the rear mounting bolts to angle the rear of the peg plate outward a bit or by using a right peg plate from a paralever bike. (You'll need an additional mounting bracket if you use K1100 peg plates.)
Your existing monolever rear brake rotor, ABS sensor and caliper will fit on a paralever final drive. The master cylinder will fit on a 4V right peg plate. (Except for K75 models with a rear drum brake.)
That's all there is to it. :mbird
Transmission Gear RatiosFor K100s the transmission gear ratios of 2V and 4V transmissions are the same. If you're converting a K75 then the first four gears are the same but the K75 transmission has a fifth gear ratio of 1.67 while fifth gear on a four cylinder K bike has a gear ratio of 1.61 - about a 3.6% difference. This means that you'll have 3.6% less torque in fifth gear and your RPMs in fifth gear will be reduced accordingly as well.
Final Drive Gear RatioOn monolever final drives the gear ratio is stamped into the final drive on the top front where it meets the swing arm. On paralever final drives the gear ratio is stamped into the flat surface around the breather cap on the top of the final drive.
Two of the more prevalent gear ratios (there are a few others) in 4V paralever final drives are 31/11(2.82 - commonly found on K100RS4Vs and K1100RSs) and 32:11(2.91 - commonly found on K1100LTs.) The higher the gear ratio the more torque will be available at the rear wheel. You'll get lower RPMs for a given speed and slightly better mileage with a lower gear ratio.
Since K100s usually have a similar gear ratio and 90 hp the torque at the rear end will be the same if you use a paralever with the same gear ratio.
Most K75s have a 32:10(3.2) final drive which is significantly "shorter" (has more torque) than the highest gear ratio available in a paralever final drive, 2.91. So if you convert a K75 to a 2.91 paralever final drive then the amount of torque available is reduced by about 10%. Since a K75 only has 75 hp there is a noticeable performance difference between the 3.2 monolever final drive and a 2.91 paralever final drive. On the flip side you'll get correspondingly lower RPMs for a given speed.
Theoretically on a K75 you should see a noticeable improvement in mileage but I really can't say for sure because I use my paralever K75 as a city bike and run it in lower gears at high RPMs to make up for the loss of torque. That and I never bother tracking mileage when city riding anyhow since there are so many variables involved.
Here's a couple of examples of K75s that I've converted to paralever final drives. I wouldn't bother on a K100. I'd just buy a 4 valve K since they have better brakes and suspension as well as radial tires and 10 more hp.
K75S: (K100RS4V peg plate)
My K75 Frankenbike: (K1100 peg plate)
edit by scott_ 10-19-13 to update missing photo's
