I've started work on fitting a K1100 front end onto my 1985 K100RS. Some parts have arrived, others have been ordered. I purchased complete used Left and Right forks from the UK and on arrival began inspection and refurbishment. The front mudguard (fender) is held onto the fork legs with 4 M6 x 35mm high tensile  bolts. 2 of the four bolts were in situ, but badly rusted and the holes on the aluminium legs they go through had a big build-up of aluminium/steel corrosion deposit. The third bolt had been snapped off part way up the thread and the 4th had the bolt head snapped off with a small amount of thread protruding from the hole in the leg. It failed to respond to cleaning, lubricating or hitting. I eventually got it out by tightening a high tensile nut on the the exposed thread. Again the problem was the aluminium/steel combined corrosion formed a very strong chemical weld. 
The Front ABS sensor is bolted into a hole on the lower fork leg. Got the 2 holding bolts out Ok but the sensor would not respond to heat, lubrication or hammering. I have decided not to to fit ABS to my K100 so sacrificed the sensor by drilling out the centre of the sensor then belting it with a drift and hammer. It eventually came out. Again, an electrical/chemical corrosion had taken place effectively welding the sensor in place to defy removal. 
I guess the lesson is when you are reassembling a front end, carefully clean any lugs and holes and apply a quality anti-corrosion/anti seize - it can save a lot of future trouble.

redrockmania wrote:I guess the lesson is when you are reassembling a front end, carefully clean any lugs and holes and apply a quality anti-corrosion/anti seize - it can save a lot of future trouble.

Ab-so-bloody-lutely. That applies to all fasteners on a bike. Don't stint with it either because you can always wipe the excess off later.

Which reminds me I need to start a regimen of penetrating oil on my ABS sensors.  The last time I had to remove one I had to mess it up pretty bad to get it out.

yep copper slip etc can be a god send

good luck with the build mate ,

I should get your address properly and call in next time down that ways

cheers

Will you be using a 3.5 x 17 three spoke wheel, callipers and the 305mm discs from a K11, as well as the 20mm master cylinder and new style (K11) throttle cable? 

Calliper to disc spacing is different between 285mm standard discs with two pot Brembos and 305mm floating discs with four pot Brembos.

Some would say it's an issue - but only personal experience with it counts - because the Paralever swingarm is about 50mm longer than a Monolever swingarm, BMW 'tightened' the front end rake/trail numbers to continue with approximately the same wheelbase between K100/K75 & K1100RS. Your steering feel may be quicker than a K100 rider is used to if continuing to use a Monoelever swingarm with a 'complete' K1100RS front end.

I look forward to your outcome.

Yes, I'm fitting a 3.5 x 17" 3 spoke from a R1100R (20mm ID bearings) . Have found suitable 25mm ID bearings so I can fit the wheel to a K1100 spindle (axle). Have new 305mm floating discs that fit. Have a 20mm diameter master cylinder and have made up a custom throttle cable (used new pushbike brake wire (far less expensive) and machined brass cable nipples and a brass seating flange that fits into the bracket near at the back of the throttle bodies.
It will be several months before I'm on the road as parts are still arriving. Will report on the steering/handling response with a 17" as opposed to 18" front rim. The 3.5 x 17 rim enables a modern profile front radial to be fitted and a big range of tyre options due to its common size.

Good, thought it through. There are some niggling details to be sorted.

You'll be making a spacer for the axle due to the wider splay of a Telelever on an R1100R as compared to the Marzocchi forks of a K11, and the fact that the Oilheads use a speedo drive gear on the left hand side, and because there's a bloody great big recess where said speedo drive gear goes in the hub of that choice of wheel when it's not present. The new left hand side oil seal size will be 60 x your axle (spacer) diametre x 7) You might also need flat head brake disc bolts due to clearance issues. The original dome heads might not clear the inside of the forks with the Oilhead wheel. Check my Big Block thread for the BMW part number and description, including piccies, of the later flat head screws which are 8x27mm but fit no worries compared to the R1100R's 8x25mm brake disc screws. 

Keep in mind, too, that on an R1100R the right hand side bearing is 20 x 47 x 14mm but the left is a 25 x 52 x 20.6mm. Have a squiz at the bearing centring or preload 'pipe' inside the R1100R wheel because it is a different part number to a K1100RS' centring pipe and you'll want to be certain the axle of your choice fits through it snugly but allows for bearing preload on the inner races. So it's proper length and ID you're looking for. Pity you couldn't have located a K1100RS front wheel - you'd almost be laughing by now.

Another thing, before you bolt it all up be sure to measure the dimension from outside to outside of the brake discs to be certain it's near as 5" (127mm) as possible for proper centring of the callipers and pads over the 305mm discs - this is done, of course, before you fab up an axle spacer.

I think you'll find it's not the 17" wheel compared to an 18" that gives you the Very Quick Steering. It'll handle like a modern Ducati due to a much shorter wheelbase if you're not also swapping out yer gearbox and swingarm/final drive for longer Paralever set-up. Steering damper recommended.

Charge ahead! This is fun.

Many thanks Twowheelsbetter - excellent advice

I thought the K100 Triple  Clamps were 84mm from centre of head stem to front of forks and the K1100 was 80mm centre to front edge of forks.

Just stick a flat edge across the front of the forks and check the centres if you have both triple clamps there.

How that effects going down a size in the front I don't know.

For the K1100 front-end modification to my 1985 K100RS 2V, the Triple Tree has arrived complete with an apparently pristine in situ Ignition Switch with wiring and connector block. I believe the switch part no is 51252323004 (not to be confused with 51252308669 which is for K100RS4V; K1; and some K1100's). There are 5 wires to the connector block: Red, Green, Grey, Grey/Blue and Violet. Is it possible to do a simple wiring adaption so the the K1100 Ignition Switch works - Advice welcome - Thanks.

Should be possible.

Here is the internals of the K1100 switch off of a 1993 model.


compare that to the K100 equivalent to see how to hook up the wiring.

Rob: I'm assuming that's a split (two part) wiper? Not being a K1100 owner, what's the R position do?

Huh. One google search later and it seems that the R position (violet wire) isn't connected up on the K1100LT.

It's one bike, one modification in the end, so one conversation as we don't want to be looking all over the place for the info. Topics merged.