Front end and cooling pre-assembly

Since I finished and/or cleaned a lot of parts and got several new parts I decided to do some pre-assembly. It is just for fitting, as some parts still need to be sprayed or otherwise modified, but it is a useful exercise to see if everything is working out as I had in mind.

So, I put the frame back on the bike and refitted the fork legs first together with the new lamp ears that just arrived and the headlight that I had sitting around for some time.

Note that the fork legs have an unusual diameter of 41.7 mm which makes finding fitting lamp ears difficult as most are aimed at 35, 38 or 41 mm. I bought nice classic aluminum ones of 41 mm diameter and spend half an hour dremeling (is that a verb?) to make these fit over the 41.7 legs. Not a big deal.

I also refitted the instruments in order to see at what height the headlight should be. Since I dropped the front end 20 mm I had to slightly modify the plastic dash cover to make it fit.

Lowered the front 20mm
Dash cover fits

I also wanted to fit the blinkers, but I spend some time on the net to decide if I should put them on the same height as the headlight pivot, or below. Results were very inconclusive: Most BMW had them below the center of the headlight, but not always, Kawasaki in the seventies and eighties put them actually in the pivot bolt, so pretty forward. Honda has had them everywhere. Since fitting them on the lamp-ears is pretty straightforward I decided to do that. Just needed to drill two 11 mm holes to attach them. I think it looks pretty classic…. (I know they’re not quite level, just pre-assembly)

New headlight and blinkers

Finally I put the radiator and fan back into place and the fuel pressure valve in order to get a better idea of how much room I have actually left on top of the engine. I need to fit a new coolant reservoir there. Turns out there is quite a lot of space with the old airbox gone.

Radiator back in place (minus hoses)
Lots of space. Plastic container will be turned into coolant reservoir

Finally a closeup of the new coolant reservoir, ie. the reservoir to be. It is actually a fuel tank for RC aerobatic aircraft which I bought at Conrad. Nice thing is that it is fuel resistant, has vent hose connections and the main connection has a brass end piece on the end of the hose so it will always be in the fluid. I’m going to make a steel casing for it and mount it using some of the threaded holes which are left over from the original airbox.

In the steel case I will make some slits on the side so I can see the actual coolant level. Might even spray it in color….

Fork legs cleaned, painted and new seals

The bike had been sitting for a few years after being driven in winter conditions and the fork legs both had weeping seals.

I took the wheel and the brake calipers off (after I had already removed all K1 plastic), took off the brace plate which holds the brake line splitter and removed the fork legs out of the frame.

Make sure to work on one leg at the time, don’t mix parts. First take the top off, which is under slight spring pressure. It won’t launch itself at speed, just press down a bit when you unscrew it.

I then removed the spring, the spring guide, the spacer and the top shim.

Then I emptied them, let them drip out for an hour so most old oil was out. I then rinsed it with clean paraffin a few times, and gave it a final rinse with some clean fork oil. That left them oily but clean.

Next step is to get the seal out. On the K1 forks this is a bit fiddly as they don’t use normal circlips (the ones with the two holes), but a simple flat ring which is diagonally cut. It can take anything from 2 minutes to half an hour to get them out…

Once out just move the inner leg up briskly and the seal will come out. Don’t throw the old seals away yet…

Put them in a vice between some wood or soft cloth, and remove the large allen screw at the bottom to separate the inner and outer parts. If you just want to change seals this is not necessary, but I wanted to spray the lower halves.

I put the parts in numbered bags, and took the picture below for reference. Mobile phones can be useful….

Fork legs after disassembly and before repaint
Fork legs after disassembly and before repaint, note where the paint has been damaged by the plastic mudguard on the left leg

I subsequently cleaned and degreased the lower halves, and sprayed them like I did with the radiator (previous post). Same process, same paint.

They came out rather well as can be seen in the picture below that I took just before re-assembly, it shows all parts of one leg.

Fork parts, from top: spring cap, spring, lower fork leg, spacer, shim, dust cap, top cap, circlip, ring under seal, bottom screw, seal, inner leg

Assembly is not difficult. Check the inner legs for pitting, and make sure to get rid of any sharp bits before putting the new seal in. You can use a small hammer to softly tap edges of pitting flat and/or a whetstone to make sure they won’t damage the seals.

Then first put the inner and outer leg together again, then use some thin machine oil or fork oil to oil the new seal. Put the shim in (hollow part on the bottom), then carefully shift the new seal in place. I cut the old seal in half with a hack saw and used the halves to push the new seal in its proper place. You know when it is seated when you can see the groove where the circlip has to go.

Finally put the circlip back in, make sure it is seated in the groove all around and put the dust cap on. Done.

Finally the spring, spring cap, spacer and shim can go in (in this order) and the top cap can be screwed on. I did not fill them with oil yet.



Air intake and filters

One of the things high on the list for this makeover was simplification. Production motorcycles always seem overcomplicated, probably because they have to comply to many different regulatory rules.

What I always disliked about the BMW K-Series were the huge bulky plastic air boxes. Therefore I simply decide it had to go. After the complete disassembly I cleaned the throttle bodies and replaced the O-rings between the intake duct work and the cylinder head. These rings came out square and rock hard.

I did a lot of googling in order to find suitable pod filters. Real classic ones with just  a metal gauze filter I thought to be a bit to open, so I hunted for more conventional pod filters. Size wise I wanted them as large as possible, but they needed to sit fairly close together so they can’t be too big. I eventually settled for a set of four K&N pods (RC-2294). Quite expensive, but better quality than cheap Chinese knock-offs.


As you can see in the picture, I’m replacing all fasteners with stainless steel allen bolts where possible. Exceptions are those bolts with a strength rating above 8.8, like frame and brake caliper bolts.

Note that the fuel rail is still missing as I need to have the injectors cleaned before putting them back in.

Technically, I still have to find a good spot for the intake air sensor which used to live in the now obsolete airbox. There were also a lot of extra vacuum tubes all around the airbox. Basically these were using intake vacuum to suck oily fumes from the crankcase breather and feed it to air filter box where an oil/fume separator fed the oil back into the crankcase while the fumes were mixed with intake air. Given the oily mess in the filter box I don’t think this ever worked well…

I decided to make this much simpler. I’m going to put a crankcase breather  filter on the main crankcase breather outlet (havent done so yet) and leave it a that. I closed up both the vent where the oil was fed back into the crankcase (on the front of the engine) and the vacuum connection on the vacuum balancing hose on the back of the throttle bodies.

Radiator and fan assembly

Over the last weeks I have been quite busy with the dismantling and cleaning of parts I want to re-use. One of the things I finished is the radiator and the fan. After disassembly I spent a lot of time cleaning the radiator. I first simply washed it, then used compressed air from the back to blow out most road dirt and debris.

Although I thought I got most out, each time I handled the radiator more little pieces of gravel kept coming out of it. I spent a few hours to dislodge the larger parts with a toothpick, used compressed air again, and concluded that more was still coming. I repeated the process several times and then called it clean.

I degreased the whole thing with industrial degreaser and then put on a coat of 2k wash primer followed by a number of coats of 2 component high gloss black paint.

The fan assembly I just thoroughly cleaned and used Valma Plastishine to make it look like new. See below for the end result after putting the thermostat back in and  refitting the fan.



With regard to spray painting it is good to know that 2 component paint is now available in rattle cans in any RAL or car color from Spraymax. They use a clever system where you mix the components in the can just before painting. After mixing the shelf life is very limited, according to Spraymax just 8 hours. If you put the mixed can in the fridge it is safe to say you can double that. See below for a picture how these cans work.