[Erman]

Once upon a time, I had an 84 Seca 750. After about a year of riding, I tore it down for a complete rebuild, but never got quite finished. This was my first time with a major mechanical project involving motorcycles, and safe to say I never did manage to sail home.
So last year, I heeded a friend's advice and bought another bike to ride while I was fixing up the Seca.
The choice fell on an '84 K100RS. It was running, it was cheap, it had injection, and it could potentially be kept running for a while.
Sadly, after discovering a thing or two about the true state of the bike, it quickly dawned on me that this bike would end up a rolling chassis unless a "deep clean" was performed.
So, October 2012, the adventure began....

 

[Erman]

1984 K100RS after purchase:

 

[Erman]

Sure, I _could_ ride it in this state, and I did for about a week before symptoms of neglect started showing...

Dripping coolant is never fun:

Replacing the seal in the water pump got more serious when I discovered that BMW had opted to change the impeller after only a couple of years in use...
So a new shaft and impeller were ordered:

 

[Erman]

Day three of riding revealed oil leaks from engine block, and I went ahead to reseal the engine with RTV:

I had the bike for an entire week before going away on a small trip with my ex, all the while a smoky exhaust did itself manifest. On my way back, I stopped for gas and that was the last time this bike ran. I had to leave it parked at the gas station - luckily a 24h shop. We picked it up the next day with a trailer, and I went ahead to look at various solutions of getting it to run again.
As nothing seemed to work, I took it to my workshop and began the dismantling process:

Ooops! That's a picture of my PC within a LEGO shell. How the hell did that get on here?

 

[Erman]

I had to build a new blasting cabinet to accommodate bigger parts. What better way to recycle Christmas lights?

To my ex's great dismay, this bike was going to be rebuilt for rider only. So there was no need for passenger footrests:

Also, the swing arm and final drive were blasted and primed:

 

[Erman]

Great attention was given to the throttle bodies. After soda blasting, these were covered with Eastwood Metal-Protect:

Some like it dirty. I don't:

Gearbox done blasting. Separate wet sump gearbox. Seriously, BMW, wtf!?

Engine covers:

And engine:

Engine and gearbox gun painted black with Bill Hirsch Engine Enamel:

Gearbox done and mounted with pedals and stands:

 

[Erman]

Frame being sodablasted:

The rear of the frame was cut and raised about 15 degrees. After paint:

 

[94yzf75fighter]

Nice start awesome bike

 

[Erman]

Thank you!

 

[Erman]

While the frame was drying, I spent time on converting the handlebars to clip-ons. I kept the original handles and controls (for now):

Time for a test-fitting:

 

[Erman]

After having raised the frame hiney, I could no longer use the stock tail piece, and a home-made style tail piece had to be made. Started out by sketching up in photoshop and created a rough model of cardboard:

However, this setup would become to problematic, and the seat pan / tailpiece were divided into two separate parts. As the cardboard model would make a too angular shape, another one was made out of Styrofoam and covered with red clay:

The fiber glass cowl was molded on top of a plate cut to the shape of the frame + the mold. The tricky part was making flat pieces of fiber glass (4 layers of stranded mats sandwiched between two layers of rowing mats) and laying one on the cut metal plate, laying the clay mold (now covered in aluminum foil) on top, and layering this with the same mat combination.
After drying, the rough model looks like this:

Next up, I cut an access hole and joined the parts together with more mats+resin, using resin to even out surface imperfections:

Looking back, I realize it would have been better to locate the access hatch on the bottom to improve looks and a literal pain in the ass. Come winter, I will make a new cowl with this in mind.

 

[Erman]

Next up, the tank and tailpiece were primed and painted in flat red (photo does now show the color faithfully), and then clear coated. I cut a plate to size and made it into a latch using piano hinges and a cylinder lock. The trim is black and white checker I got from Ebay. At this point, because I am going to redo the tail piece, I am not concerned with how hideous the latch is. My ass does a nice job covering is anyway.

 

[Erman]

The stock licence plate holder is just a molded soft plastic piece boltet onto the tail, and rear indicators were hardpoints on the tail piece. I wanted to convert indicators and brake light into LEDS, and got hold of a licence plate bracket from Ebay. I fitted this out with a standard brake light / running light, indicators with built in running/brake light, and a licence plate light. All E-marked and required by the authorities.

 

[Erman]

Because I removed the stock handlebars and went for clip-ons, it would be weird to keep the instrument panel stock. In time, this one will be converted to a Koso. There are two threaded holes on the lower triple tree and two on the upper. I made two L-shaped brackets to support two struts, onto which the dash was fitted. The stock option is too flimsy and vibrates even under slower speeds.

I finished up the front en with a cheap front fairing I found at the local import store. I relocated the horns to under and behind the front fairing. The plastic parts that look like they're carbon fiber were also painted red to match the tank and tail piece:

 

[Erman]

Trying out the airflow sensor with the stock manifold:

The stock setup included a lot of plastic parts - almost as if they wanted to fill out the space between tank and engine. These were removed and replaced with a custom air filter in front of the airflow sensor. Also a new, straight, manifold was bought to save space:

Coolant overflow tank on the stock bike was a black plastic container located to the right of the battery. This one was relocated next to the airflow sensor:

 

[Dougiealan]

Looks good.
http://www.customfighters.com/forums/showthread.php?t=65918

 

[TrevTastic]

That's really cool!

 

[Erman]

The build was practically complete at this point, and I took her out to fresh air one Saturday morning. The starter relay is diagnosed to be faulty, and I suspect that the bike refused to start at the gas station exactly because of this. A new relay is ordered, and I'm hoping this will end the need to fiddle with the relay every time I want to start the bike.
After idling with white smoke for a while, I decided to hop on and go for a ride. After all, what's the use of having a bike if you're not going to ride it?
The white smoke kept on for about a mile, and then died off. I suspect this was due to the new head gasket that needed to expand and set. Incidentally, the Seca also has a new head gasket, and a cold compression test showed lower comp. in the two middle cylinders. But I guess this will improve once I've put the engine through a heat cycle.

Anyway, some sore eye candy:

"What up, yo!":

 

[Erman]

One thing I immediately noticed after starting to ride the bike again, is that it gets hot under the seat (and tank), because the fan blows directly towards it. Since I can't re-position the fan, I went for heat shielding under the tank and seat:

And a new funnel had to be fabbed for the air intake. The residue under the air intake funnel is part dirt and part coolant. I noticed a few drops at the thermostat. Because it's not dumping coolant yet, I figure I ride until it does.

 

[Erman]

So that's it for this build. I will put up changes on the bike as they happen. Because the bike is so old, changes are bound to happen.

I also experimented with a hugger for the rear wheel, but this is impossible due to right side only swing arm. Later model R1200's have a hugger mounted at two posts on the final drive. Somewhere down the line, I may be able to make it work.

The current exhaust is fully usable, but big and hideous. I have plans on making an exhaust collector and sweep the headers to a muffler as shown:

Also the following are on my wish list:
- new tailpiece
- small battery in the tail piece
- solid state relays
- dual vertical headlights
- Koso dash
- variable clip-ons