1978 BMW R100S

Purchase Date: April 2018

Another motorcycle? Yes, another motorcycle.

I've always admired the larger airhead BMW motorcycles. I wanted a black one for a long time but the prices can be just a little out of reach for a motorcycle I can't really justify owning.

A few years back I was the lucky owner of a fun little white R60 and have regretted parting with it. The bike was a great little grocery-getter, unfortunately it didn't make the cut driving on the fast freeways here in the CA bay area. The R60 was also the bike that my girlfriend Hillary learned how to ride on; because of the attachment she still gives me a bit of a hard time for letting it go.

A few years later, it's 2018 and a black '78 R100S shows up for sale on an email list that I'm part of. The price is good albeit the bike does need some work to make road worthy, this is the ideal scenario for me. I don't necessarily need the motorcycle but how can I pass this up? I think I can justify this one.

The "good deals" get snatched up quickly. We all know this, so I couldn't wait and "think about it", I had to make a move on the listing ASAP. That I did, and the owner promptly replied with photos. I was sold right off the get go.

The motorcycle was located in a small town, northern CA bay area - just under a 2 hour drive for me. Upon arrival I was welcomed with the owner and a few friendly dogs. We walked into the well equipped garage where I was immediately awestruck by the collection of over a dozen motorcycles, a few vintage cars and machining equipment all neatly crammed together in perfect harmony.

The owner and I immediately started to converse about all or the motorcycles and cars surrounding us. So many toys, the owner is a lucky man. It didn't take long before he and I made our way to the R100S resting on a lift waiting for my inspection. I didn't have much to look over, I knew I wanted the bike. The BMW started up with a rough burble and cough, I didn't even expect that much. Without hesitation I let him know I was interested. To make a long story short, we swiftly wrapped up the deal and I was on my way home with a 1978 BMW R100S in the back of the truck.

The 1978 BMW R100S has a 980cc opposed Boxer engine with 2 valves per cylinder. The air cooled engine puts out 56 ft-lb of torque R 6000 rpm. The BMW has a dry, single plate clutch and 5 speed gearbox. Top speed is a modest 118.5 mph. This bike can do the distance with the 6.3 gallon fuel tank. At 484 lbs wet, the motorcycle is equivalent in weight with modern sport touring bikes the same size.

After arriving at home I went to pull the large BMW off the truck finding out the front brakes were practically locked up. I've seen this before on airheads in the same year range, it's typically due to corrosion in the master cylinder clogging the passageways - not letting the fluid circulate. Anyway, I buckled my knee (a minor, painful price to pay for the BMW) while pulling the bike backwards off the truck. A few more struggles later, the motorcycle found itself tucked snugly against the garage wall, in line waiting for a 2nd life. The previous owner didn't drive it, he just bought it to fix up from the owner before that - which never happened; paperwork listed the bike purchased in '98, it's now 2018. That's a few years sitting; I'm surprised the battery held the re-charge just enough to start the bike.

A few weeks later I notice a rather large puddle of oil on the ground underneath the left cylinder head. Looks like a general seal / gasket change is needed, a good start to go over the bike. - Of course this will go along with the front brake master cylinder rebuild. New brake rotors are also in the not-so-distant future for this motorcycle.

The seat is barely hanging on to the frame, the lock and bracket holding the seat are both in poor shape. Something else to give attention to.

I really admire this BMW, I've been hoping to find one of these in the garage for some time now. I'm looking forward to bringing this one back to life.

June 2019

I've had this bike in the garage for over a year now and haven't done a thing with it. I finally have the Beemer on the lift and I'm starting to take a closer look at it.

Final Drive: The fill level screw is gone, just noticed this. And not gone in a good way, the threads are completely stripped - gone. Not to mention the drive has no oil inside. Another item to take care of added to the list.

Braking: The front brake master cylinder was not functioning correctly. I replaced the piston + orings and cleaned up the housing. All in all this was an easy cylinder rebuild. Parts from the Beemershop in Scotts Valley CA. A final flush appeared to do the job and the brakes work well once again.

Valves / Cylinders: I removed the valves and cylinders to "freshen it all up" and found all kinds of fun mistakes done by a previous owner. This includes: stripped threads, cracked - over torqued connections, gaskets where there shouldn't be gaskets, exhaust side adjustments with zero clearance; and I keep finding more errors as I go along. The good news is the cylinders are in good shape , holding to specification. Nothing major wrong surfacing from the tear-down just yet.

September 2018

Valves / Cylinders continued: Valves have good seating, springs were out of spec - I replaced them with OEM springs from Wunderlich. I also replaced the worn rings with an OEM set from boxer2valve, along with the new gaskets and seals tidying it all up. I personally use blue hylomar gasket sealant, I found that it works best for me.

Starter: The starter on the BMW was tired. Instead of rebuilding I ordered a new one, an eBay special. The price was right although fitment was sub-par. I found myself making a new grounding bracket along with adding some all-thread for the main mounting hardware. I also discovered a spider nest in the starter handlebar switch along with a faulty wire connection to the relay. I cleaned up the cobwebs and rewired the relay assembly with a new old-stock relay.

Final Drive: The final drive assembly is all cleaned and freshened up, the stripped threads were not as bad as I initially thought.

Wiring: Someone with poor wiring skills had their hands on this BMW at some point. The added / removed / poor wiring that was completed outside the factory harness is poor. Frayed wires, loose connections and un-terminated connections are plentiful and a major headache. I'm correcting and cleaning up everything I come across. At some point, if this motorcycle turns into a long term bike I will replace with a new complete wiring harness.

After closing up the engine cases, re-installing the carburetors, and wrapping up some of the loose wiring, I attempted to start the bike to find out where I currently stand with the mechanics. It didn't take long for the gas to reach the carb bowls and the vapors found their way into the cylinders when the bike fired right up. It only took a few seconds and the liter bike found itself humming along at a nice steady idle. Ah, what a successful feeling - standing back from the BMW as it sits at a steady idle. The engine is burning off various oils and chemicals on the cases, exhaust odors and the smell of gas, smells good to me!

October 2019

Seat: The seat did not sit correctly on the bike. The seat pan is bent and cracked so bad to the point that the brackets holding the seat to the bike are misaligned. For the mean time, I shimmed the brackets with washers and longer screws for an easy re-alignment, voila - the seat fits again.

Ignition: Currently, the ignition circuit runs well. I am still working out all of the bike's electrical gremlins. I replaced the condenser; the new points are on hand ready to be replaced another day. After everything else checks out.

The BMW has been shuffled around the garage all too long. I'm beginning to get both impatient and excited to get this bike back on the road. I still have to wrap up some wiring on the front end, re-establish mounting for the fairing (original was bent out of place), lube all of the cables, and change the remainder of the fluids. After that, a few test rides - then to clean it all up. I will re-lube the spline, install the new points (+check timing) and re-torque the heads at the same time after some miles have been accumulated.

November 2019

Ignition (continued), Carb Sync: The carburetors were out of synchronization. I re-sync'd them. Installed new points and re-set the timing (using the static, timing light method). Before these updates, the bike had what sounded like a bottom end knock. I initially thought it might be a bad bearing, luckily the sound disappeared after the adjustments.

As usual with these projects, I gave Beemer the a complete service including new plugs, new battery, lubed cables, new fluids, etc...

December 2019

Brakes: Something is going on with the front brakes aside from the master cylinder rebuild; brake fluid is corrosive stuff and it can wreak havoc sitting over the years. I installed new pads and the left side adjusting shaft appears bent, or the lower fork leg is bent, I'm not quite sure at this point what is off. I'll re-assess this problem in the near future.

Test Drives: Upon initial test drives there are some issues. Not surprised on this one, I've been finding one problem after another. The bike runs smoothly, there is a low end knock upon initial acceleration, this may be normal for the year - I'll have to do some research on this before diving into bottom end bearings (no metal filings in the oil filters).

More problems; another electrical short in the wire coming from the starter button housing, not surprised by this being the short is coming from a small bundle of electrical tape that I have yet to inspect.

And the wobble! A horrible front end wobble, I believe this is due to dragging left brake. Something is bent or needs a rebuild. The BMW is being pushed aside to work on another day.

Photos and details of the R100S will be added as the project matures.