What models and years driveshafts will interchange with 20 spline K100? Looking through Fleabay it looks like K1100 an K1200 might fit. Also, it looks like R1100 might also fit. May need to lengthen the s.a. to suit. I am looking for something that will fit. Any info?

92KK 84WW Olaf wrote:20 spline refers to 2v Monolever shaft used in some 2v K100 and all 2v K75. Not 4v K100 and also not K1100/1200, they are Paralever. Also early K100 have16 splines.

My mistake. I had an early 85 K100 and I understand that the spline was changed later, but I don't know what the cut off was. And to show my further ignorance, I don't know whether we are talking about splines on the transmission end or the fd end.

Hi mate, I don’t the answer. How ever can I ask if you are wanting to replace a worn out drive shaft or wanting to change the final drive ratio? 
I recently serviced my 85 K100rt, it was still in good shape and I always neglected it. 
Porto

20 spline refers to the final drive end. The gear box end did not change. Be aware you can actually buy a new splined end for 20 splie shafts and have it welded on to the drive shaft at a machine shop.

At 1985 you may have a 16 spline shaft, you need to check this out more. If you do, they can be harder to find. I have 2 Ks on 16 spline final drives but also have 2 31/11 ratio spares for them.

You can find a 20 spline final drive and 20 spline shaft and just pop them straight in. Mostly the final drive ratios are 31/11 for RS and 32/11 for RT/LT. Its a small difference and I would go on condition/price rather than focus on the small difference in the ratio. A K75 one for rear disc brake will also fit BUT the ratio on those is usually 32/10 but thats a bit out for you at 10%. The ratio is stamped on the top of the final drive casing.

OK. I am confused. I thought the early mono lever K's had the 16 tooth spline, but I was perusing Fleabay and found an 89 driveshaft with a 16 tooth spline. So, which is correct. The final drive I have is a 20 tooth spline.

IIRC it was part way through 1985 that the change to 20 spline shafts was made. If you have seen a 16 spline shaft from an 89 model then it has replaced a 20 spline along with the final drive from the earlier model. Remember all the K100s are at least 30 years old so most have had many parts replaced with used parts from wreckers. I doubt that there would be many if any that have all original parts.