Hello everyone.

My name is Tony and I come from (beautiful) Far North Queensland, a place called Clifton Beach, about 25km north of the city of Cairns. I own three currently non-running  K100RS bikes, two of them are donor bikes to restore my 1986 edition that was parked up by its owner only a few months after purchase. It was kept in a shed under cotton sheets and the finish has largely survived the decades pretty well (in fact after a wash it looked close to immaculate) but unfortunately generations of rats made their home on top of the engine and nearly all the wiring and all the rubber in that vicinity are destroyed (hence the need for donor bikes), also given that the intake ports are filled to the brim with rat detritus I hold no hope that the engine has survived in an easily restorable condiiton, but I will eventually investigate.
 
The K-bikes are currently at the back of the restoration queue, I expect to get to them when I retire in 3 or 4 years time.

I do admit to my being here at present is somewhat under false pretences, but I will explain below. My primary interest is BMW Airheads, I have a 1978 R100RS that I've owned since new and a 1984 R65 that was bought in 1995 with a blown engine to be the spares donor to repair my wife's R65/80 (1979 R65 with 1987 R80 engine fitted) that was backed over by a truck whilst it was in my care. Five years ago I decided to clean up the 84 R65 with the intention of cataloguing the bits that would shortly be for sale, somehow I ended up spending a minor princeling's ransom to mechanically restore it to rideable condition.

Ok, longwinded but the relevance to this group is coming shortly, I promise.

I am a member of a local restorer's club in which most of the members own early Honda 750s and Kawasaki 900/750/500 and a smattering of Suzuki and Yamahas, only one other member has BMWs - an R65LS and a R1100RT (which scrapes in on our 20 year old rule).

Now I rather like my R65, but it is frustrating when we go on club rides to the nearby Atherton Tablelands in that whilst the R65 will comfortably out-handle any old Honda-4 or Kawasaki of the same or older period, it just doesn't have the urge to stay with them going up a 19km long hille. Hence a plot was hatched to dramatically improve the R65 whilst keeping the modifications pretty much invisible to someone who does not know BMWs (the other BMW owning member is aware of the plot and is chortling from the sidelines). 

So the first step is a capacity increase and one of Messrs Seibenrock's 860cc kits has been procured. In addition, an R75 final drive has been obtained in order to tame the revs a little. 

But this still left me with a basic grip problem due to the narrow tyres fitted to stock R65's (well really all airheads of the era) and the realization that if I managed to fit a wider front tyre, the forks would flex enough to negate the grip advantage - hence a K100RS front end has been obtained and I am currently grafting it onto the Airhead frame - this is proving to be ridiculously easy by the way.  I had some queries about suitable fork fluid and a member of the R65 forum, who likewise suffers from what he refers to as "K-Pox", referred me here. 

Some people may be interested to hear how similar the early model K100 forks and internals are to the R85/R80ST editions, the K100 forks are truly nothing more than a scaled up copy of the R65 forks, which isn't a bad thing at all. The larger diameter tubing reduces flex and the wider front rim will mount a far greater array of desirable rubber than the snowflake ever could. Best of all, when coupled with an R65LS rear wheel, the K100 front wheel is sufficiently similar so that the casual observer will never pick the mismatch. I have obtained a pair of 4-spot Brembo callipers from a later model K100 to bolt on in place of the F08s and lastly have a fork-brace ready to fit.

So that's why I am really here - looking for technical assistance in pulling off what once would have been called "a wizard jape". 

Oh, one final thing.  I don't need advice along the lines of "you will upset the handling", "it will be unstable" etc. Firstly the front end geometry is remarkably similar and when fitted the geometry will change less than the stock bike would change with different loading/tyres fitted. Besides fitting K-bike front ends to Airheads is a well traveled path and is known to dramatically improve handling.

Welcome Tony, 

Glad to see you decided to pop in and say hello from the R65 forum. 

(Burt) the TacKler.

Welcome to the asylum.
Regards Martin.

Oh I do so like that idea Reminds me of the time two of us fitted a Honda FT500 engine into an RS250 frame. Difficult to tell the difference externally (it was the same shape as the 250 but had been injesting a few steroids) and went like sh!t off a shovel...

There's something niggling me about the 4-pots. IIRC you'll have to do some machining on the mounting bosses to get them to fit.

Dai wrote:
There's something niggling me about the 4-pots. IIRC you'll have to do some machining on the mounting bosses to get them to fit.

If that proves to be the case I won't use them, the F08s are capable of supplying all the brakes an R65 needs, fitting the 4-spots was/is nothing more than a vanity idea.

Dai wrote:Oh I do so like that idea Reminds me of the time two of us fitted a Honda FT500 engine into an RS250 frame. Difficult to tell the difference externally (it was the same shape as the 250 but had been injesting a few steroids) and went like sh!t off a shovel...

yes, there is an especial joy a=in building something that surprises the be-jesuz out off the intended target.

Not my first rodeo, in the late 70s I fitted a Pursang engine to a Metrella and that proved fairly exciting. At a much higher level of illegality I hung a headlight and tail/stop light connected to a total loss battery system onto a TZ350, that proved terrifying.

You will also need the 20mm master cylinder and that means a K1100 throttle setup. It is not as straight forward as it first seems. Many have found that a complete K1100 or K100 16v front end the easy way to go.
Two Wheels Better did do it using Suzuki discs but even that was not straight forward. There is a write up on here somewhere about it.

RicK G wrote:You will also need the 20mm master cylinder and that means a K1100 throttle setup. It is not as straight forward as it first seems. Many have found that a complete K1100 or K100 16v front end the easy way to go.
Two Wheels Better did do it using Suzuki discs but even that was not straight forward. There is a write up on here somewhere about it.

Nope, I won't need to do that, I have machine tools. 

if I need to do go to a larger bore master cylinder I'll simply bore and sleeve an existing airhead master cylinder and fit the most appropriate size pistons etc.

And yes, a nice set of Nissin 4-spots would look a treat, but would clearly not be BMW and give the game away don't you think? Remember, this is a "sleeper" build.

Yeah OK