BMW R100CS: Airbox Conversion Part 1

[@andrewd7586]

Owning the 1980 R100S, which is absolutely original in specs & aesthetics, I’m still of the opinion to keep yours original. Once you go down the path of a mod here & there, before you know it, it’ll be nothing like it was originally. Having said that kudos for the detailed resto you’re doing!👍🏼😎

[@WildlifeMoto]

Thanks Andrew. I agree, original is best. For this build, I’ve allowed a couple of small updates to either improve performance or retain the classic styling from previous airheads. I’m keeping and restoring all the original parts, so I can always get back to 100% original at any time.

[@andrewd7586]

@@WildlifeMoto Smart cookie.👍🏻😎😆

[@Gambo916]

Nice find.......much more pleasing to the eye than the Tupperware airbox.

[@WildlifeMoto]

Yes I got lucky finding that starter motor cover in such good condition. I agree, the old design suits this model much better than the plastic airbox.

[@stewy62]

I always thought the plastic air boxes looked horrible, although as you say okay on a GS. In my opinion you’re doing the right thing for your CS.

[@WildlifeMoto]

I agree. It just doesn’t suit this lines of the engine and transmission. As my bike is a CS, I’m happy to bring her back to the original look as much as I can.

[@peterlamont1533]

The engine breather outlet into the RH carb intake was always a problem on my R75/6 so I obtained a pair of the R90S covers with the holes and used the holes to route out a tube feed and return so that an oil catch can could be incorporated. This can seems to work well and traps mainly water from the breather fumes.

[@WildlifeMoto]

I was planning on running the breather hose into the RHS and blanking off the left. Might need a bit of experimenting to get it right. Other option is to keep the T line and run into both sides.

[@peterlamont1533]

My bike leaks oil a little at the pushrod seals. When I tried a T piece to route into each carb., it resulted in more oil leak. This I interpreted as a higher crankcase pressure because of the reduced breather flow due to the T piece. I modified the breather outlet casting by fitting a 15 mm plumbing tube outlet on top of the breather casting and blocked off the original, horizontal outlet. Now, I have about 25 cm of large bore, flexible silicone tubing to the catch can and back to the air filter. This looks to have reduced the oil leak seepage. Yes, OK, I should replace the cylinder gaskets and seals - on the list! My local roads have cow pats, sileage and mud so the oil seeps serve a purpose.@@WildlifeMoto

[@AnalogDude_]

BMW R10GS has a paralever swingarm that almost looks like the R1150 swingarm, but the R1100 models have a pretty chunky swingarm. Both the R1100/R1150 final drive input shaft looks very much the same as the R100 paralever final drive input, one could be machined and use ina total other model. You should search a R1100 wireloom with ECU that came form a running engine, some location to hide a audi 100 or so fuel pump, fuel regulator end ECU It seams there is someone that sell alternators for R100 to make that conversion possible. Second hand throttle bodies are cheap relative to new price. Than it will run anytime and perfect, a bit more aggressive. the R1200, some RninT, R1250 and so have drive by wire, there is a motor on the throttle body. I got the R1150RS rear frame and handle bar controls from a donor bike to change to 6 speed with hydraulic clutch. the handle bar pumps look like new, accept you need a a lot of parts to be usable, they all sell them totally dismounted even without the actual handle. But you can buy them still new. just n time, i guess also gonna change the final drive to GS model to have the split screen / mudguard of the GS and some other benefit. I know a driving school in Germany that has R100 standing in the shops window and it looks pretty good.

[@blazesboylan7947]

I’d happily sacrifice a few horsepower for those. Nice find.

[@WildlifeMoto]

Cheers. I’m not sure it’s going to make a noticeable difference either way. I certainly prefer the classic look though.

[@dullbrass]

I was thinking about it as well. I wanted a /7 but ended up with an RT that's getting stripped :)

[@WildlifeMoto]

Thankfully it’s a fairly straightforward swap once you have the parts. If you are going for the /7 look, it’s a must. Good luck.

[@dullbrass]

@@WildlifeMoto Cheers. Looking forward to the installation video.

[@mikeclaessen2985]

Nice video! ;) I have a BMW R80RT that I’m rebuilding towards caferacer probably. But I was wondering currently my bike has the flat air filter box. Can I use the same air intake ducts to my bing 32mm carbs? If not do you have a part number for the correct ones? Thanks a lot

[@WildlifeMoto]

They’ll have to be changed. Best to give the guys at Motorworks or Motobins a shout. They might have so me used parts they can sell you. You'll also need to think about how you are going to route your breather hoses.

[@AnalogDude_]

I checked the parts catalog for your bike. Do you recall what crown / piñon gear you have in your final drive? 32:11? If you install 33:12 you have about 5.5% more torque and less top speed. there is also: 34:8 witch is huge leap in torque and much less top speed.

[@WildlifeMoto]

I have no idea. I’ll look into it. Cheers.

[@AnalogDude_]

@@WildlifeMoto on the R1100x's is stamped in the final drive casing as 33:11 or so, behind the breather hole. as is, It wont set any top speed records. but you can set the 70 ps to work and get along nicely with the current traffic. it seams the "33:12" gear set can be found in shops, no indication for the 34:8.

[@WildlifeMoto]

⁠@@AnalogDude_Mine is 32:11

[@AnalogDude_]

@@WildlifeMoto was it stamped on the final drive? i use the parts catalog of a German BMW dealer (Leebman), witch is different then the regular BMW catalog and there where 3 indicated. Just in case you didn't know, it means 33 teeth on the crown gear and 12 teeth on the piñon gear. using a some online calculators you can figure out how much percentage torque you gain, someone made an extensive BMW gearbox/drive calculator, are you going to try some detective work to see if you can source the other drives?

[@WildlifeMoto]

@@AnalogDude_Yes that was the number stamped on the drive.

[@stevesanelli90]

WM, I wouldn’t bother. Leave it as standard. Nothing wrong & just as beautiful being original ❤️

[@WildlifeMoto]

Cheers Steve. Original is probably best, although I really do prefer the look of the older airbox and rocker covers. All the original bits are being restored and saved so I can go back at any time.