Hi to all I just purchased a 85 K100RS for my first non-Japanese bike to
rebuild. The previous owner had noise at low rpm's and decided to tear
the bike down to replace the output shaft. He found out it was a
bigger job than he though and lost interest in the project. So now I am
the next in line and I am kinda at a loss where to begin. The engine
has 144000 miles on it and I have been thinking I might re-ring it and
bore it out a little or at least hone the cylinders. I have been
looking on this site but I am having a hard time finding a "here's what
you need to replace thread" so if anyone can direct me to that I would
greatly appreciate the help. Here are some pictures of what I am
starting with. Looking forward to the build.



So this is whats been done so far. Now to make a list (with the help of the forum) get the parts ordered and start my winter project.

Not too many people in the US actually will rebuild the old K bikes. There are plenty around and they don't cost much. I know a lot of the guys down under are rebuilding them but I understand there are not many to be had and parts are costly. I have a garage full of what I call parts bikes I am sure some of those guys would be putting back in service. I am sure some day parts will become harder to get and cost more. But till then when one stops I just put my plate on another and keep rolling.

Hello and welcome to the site where you will find lots of information, The bikes are pretty much bomb proof, to the extent that there isn't a need to replace anything to really improve them. That said because our bikes are getting on a bit you won't go to far wrong with replacing the rubbers that are found lurking all over the place!

As for rings and boring.... The cylinders are nickosil lined which is incredibly tough stuff if you were to measure the cylinder bore with the current piston rings you will find that the clearence's will be spot on. The only time it's needed to replace rings is if your suffering from low compression that can be pointed to rings rather than valves.

The best thing to do is a real good clean up of everything or just build her back up and ride her to figure out if there is a problem.

The output shaft will be obvious if it is needing work, the rivets can come loose but if there not then it's all good....

noise at low rpm.... that could be a number of things which just a tune up may have solved.... an output shaft would have made noise at all rpms....

I have picked up all the above since joining the forum and rebuilding my K and I am sure others will have bits to add....

Twincarb

I understand the output shaft is a weak link and as you can see from the pictures the original one did have a few of the loose rivets. Ok I will not mess with the rings but what do you forum guys thing of rebuilding the oil/water pump? How about new valve stem seals? Any thing I should check with the valves them selves? Cam Chain and guide replacement? I will most certainly replace all the rubber bits, radiator hose and those rubber parts, lube and inspect the drive shaft splines. I wold like this bike to last me many years to come as I will be liquidating a bunch of the Japanese bikes I currently ride and just keep a select few.

You will find quite a few of us have stripped the water/oil pump I did mine because I had the bike apart, when putting it back together BMW have released some updated parts. Have a look in the How to Section to see some good examples. If you going to strip the top end down then it won't do any harm in replacing the valve stem seals. I replaced my Cam Chain because I had no idea if it had ever been done, I also had a rattle from the front end. The valves like all valves do wear over time but I don't think your engine has enough miles on it to be having any problems there... but a quick bedding in wouldn't do any harm esp if you strip the top end to see what it's like inside. They are simple to work on I have found.

I guess it's a question of how much work you want to put in before getting it running again to find out what may need working on. You could get the engine running now and rebuild the bike with the intention of riding her to find out if there is anything that isn't right by doing the following give her a good service, replace oil, filters, spark plugs, check the valve clearances, set up the timing and take it from there, possibly sort out the bodywork etc

Or you could follow Halo's lead and strip her down entirely and replace everything that could need replacing (that would include the rings etc) and have a bike that is ready to go in 6 to 12 months. It all depends on how far you want to go.

Have you had the pleasure of riding a K before? they are a very different beast to the jap sports bikes. Some people don't get on with them.

The gear box's are rock solid just don't use clutchless gear changes which you can do on Jap bikes. There have been a couple of instances of a grub screw in them coming out but it's not to much of a pain to sort it out. You may want to take a look inside to ensure there is nothing obvious wrong with the gear teeth... Again there is a write up in the How to section.

A popular mod is to put in relays for the headlights, this means that the full current isn't being routed through the handlebar switch. Have you got ABS on your's?

Hi Bomber 737 Twincarb is spot on I can tell you now the last owner really missed out on a good thing, these old girls are fantastic to ride and are bullrt proof don't worry about the top end now they are invincible. Just do the uasual suspects which you have already found with your good research, OP shaft, oil/water pump its a dual pump if it hasn't been rebuilt before (pump) there are just a couple of extra bits to purchase goto MotoBins web site UK based for fantastic parts at great prices with world class delivery

Halo

One that I forgot was the tank..... check the state of the fuel lines inside if they need replacing there is a specific type... The state of the fuel pump may be a slight concern mine died while I was working on the rest of the bike...

Great thanks for in information guys. Is there anywhere to source parts at a descent price in the states? I have been happy with kenda challengers for rubber on many of my other bikes. Any thoughts on tyres for the beast? So now I am planning on rebuilding the oil/water pump and replacing the timing chain and checking the vales. Along with the other normal maint stuff. One thing the prev owner did tell me was the second low fuel warning stopped working. Any fix for this? I am sure there is more but I don't have the bike in my shop just yet. One last thing, can you swap the 12 rivet out put shaft into an 85 with a 6 rivet out put shaft?

G day Bomber you certainly can swap to a 12 rivet output shaft
Im running Dunlop BT 45 tyres on my RS not bad wear and traction but
the rear will light up in corners if you give it a fistful ( hmmm nice black lines )
Not sure about sourcing parts in USA but we get ours from the UK here in Oz fraction
of the price of the steelers.

cheers Tony

Hey all, as far as I know it does not have ABS and I am very comfortable tearing things down. I have the whole winter to get this K back on the road so while I have it torn down I thought I would do it right. I don't think I will go to the extreme and make it a concourse resto. I just want a rider I can enjoy for the rest of my riding life. I think it will make a great bike to compliment my Suzi GS which I absolutely love. As for the ride quality I think the BMW fork springs are .85kg/mm while the most of the stock Jap springs are set at .45kg/mm so I am sure this bike will be more to my liking. I like a stiffer/less front end dive fork. Becuase of this I was forced to put cartridge emulators and 1.1kg/mm straight rate springs to make the ride descent in my GS. Has any one here done cartridge emulators in their forks? If you have how does you bike ride compared to stock?

I got my new (new to me) 85 K100RS home and had a chance to look it
over. It seems complete but I wont know for sure until I start putting
it back together. I know already that I am missing the windshield but
that's about it. It did some with a BMW tank bag and hard sided
luggage. The previous owner replaced the out put shaft already so I
know that's good and he included the old one and a spare. I have
replaced the fork oil and put new tires on the rims so far. I did not
tear this bike down I am at a loss where to begin with this rebuild
other than what I have done already,. Any thoughts? Below are some
pictures of where the bike is right now. There seems to be a crack
right behind where the shock mounts and I am not sure that the two
things on the right side of the frame are for. And the 4 bolts on the
head stock. Any help would be appreciated. I am planning on re welding
the crack and putting in a doubler plate.

I look forward to what you guys and gals think and any help you can shoot my way.
Thanks in advance

Bomber, take a look at this thread of a rebuild: http://hrsbstaff.ednet.ns.ca/bvogel/K100/K100.htm

I can't see the pix yet, you may still be loading them. Judging by the first photo you posted I would be reassembling the engine first, starting with the bottom end, output shaft area. Can you get that far or need more guidance?

bomber737 wrote:and I am not sure that the two things on the right side of the frame are for.
And the 4 bolts on the head stock. Any help would be appreciated.

As Club C says, no pix yet.........make it bit difficult to guess what you have in mind at the right side of the frame.
But the four bolts at the headstock is for the fairing bracket.

I am working on getting the pictures up. Having trouble with it. It has a new(used) output shaft installed. Well it seems they are up for your pleasure. Thanks for the rebuild thread. I will be looking it over tomorrow when I am sitting on a beach in Punta Canna

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Here are some more. I dont know why these mounts have had the paint ground down..
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Whataya talkin' 'bout?? It looks almost completely assembled...

Seriously, you are about 2 full days away from fire up...

bomber737 wrote:Here are some more. I dont know why these mounts have had the paint ground down..

The mounts is for the radiator cap/filler neck.......
it probably been a leak at the cap........coolant attacks paint.

welcome Bomber RJTucker has tons of good used parts he has saved my bacon once already also check with ibjman he has some parts too between to two should find all the best used stuff Where are my glasses need the for the small pic

Looks like you have yourself a great project there Bomber, from the pics it looks pretty clean.

Good luck and welcome to the forum.

Thanks for the welcome. Sorry the pictures are small but if you click on them they open a new window or should and then they get large. At least they did on my computer. I guess I will start with the electrical and move on to the cooling etc.. I can't have the paint looking like that so it will get repainted behind the collant filler and there seems to be a leak where the brake line goes into the tripple tree. The crack behind the shock mount is bothersome. It was welded before and I am not sure if I re-weld it if it will crack again. Has anyone else had that webbing crack there? Thanks a lot for the users to get parts, I will be contacting them when I know exactly what I need. Turns out this bike has 149,000 miles and it came with all the maint records from the previous owners.

Grind the old weld down and then v groove the crack, re-weld, see if it is possible to weld on both sides of the crack.