I guess I need to complete the thread - it's done. I managed to fire it up, adjust the timing and carbs and put about 100 miles on it. No smoke, good power, no weird noises - it seems good. 

A few minor issues - I had a leak from the primary and the clutch wouldn't disengage fully (making finding neutral impossible). When I pulled it down, I found the infamous circlip behind the clutch basket deformed and out of position. Yes, I did only torque to 40ftlbs, but it still failed. When I replaced that, and the seal - the leak went away. 

I also found the neutral light switch was screwed in too far which also screwed up finding neutral. This adjustment seems kinda touchy. I think either my switch is going bad or the bump on the shift plate is worn. I managed to find a workable medium.

All in all, I'm very happy with the bike and hope to get many miles out of it. 

UPDATE: Replaced the neutral switch and also opened up the tranny. I gently smoothed out the neutral light "bump" on shift selector plate and spent a lot of time with the switch adjustment. I also shimmed the Hyde shift pedal (it was kinda sloppy on its pivot shaft). Now it finds neutral better, but still not as nicely as my other '75. I suppose there's more "fettling" to do...

Since I mounted the vintage Hyde rear sets AND decided to delete the electric start components - I kinda got myself into a corner. The stock kick start lever fouls the Hyde foot peg such that you have to mount it rotated underneath the peg. This would severely limit the total throw you'd get to kick it over. I didn't feel that would be very successful. 

Anybody into Commandos will tell you that the bike was apparently built around the horn. The stock location is deep in the center of the bike, difficult to get to - not the greatest place for a horn to make sound. My original horn ended up being bad, so I needed to replace it. Further the original Lucas horn was probably everything Lucas thought it should be, which as it turns out, is pretty much the same as how they designed and built everything.  So I wanted to upgrade to a pair of Fiamm Freeway Blasters located in a more strategic position .I also needed a place to mount my new fuse block,  the Fuzeblocks FZ-1. 

I decided to mount all this stuff aft the air cleaner, but in front of the battery. My first goal was to model the space in Fusion 360, so I could design a way to get everything located. Once I had that, I designed a sheet metal mount. It took about 5 iterations to get it to work. 

Once I had a design, I used Fusion's sheet metal tools to create an unfolded 1:1 plan of the part. I glued this to a piece of sheet metal, then cut and bent it along the lines. Once I had it bent up, I welded it together and painted it.

Everything pretty much fit as I hoped it would. 

Here's the thing partially wired. In order to mount it, I welded a could of pieces of angle to the battery tray and then attached some captive nuts to be used with some horizontal bolts to secure the horn mount (you can see a couple of slots in the picture above - bottom of the front rail). So the horn mount slips down on top of the rails and 4 bolts are inserted horizontally to secure it. 

And here it is mounted up. I'm pretty happy with the way everything ended up. The horn relay is a bit cramped, but normally not a service item. Now on the the next part of the project - the wiring harness!

This project started as the result of a failed earlier project. I had attempted to build a motorcycle logger - i.e. a platform to record as many things as I could manage during a ride. I had rpm, gear, head temp (left and right), oil temp, oil pressure, speed, GPS location and ambient air temp. I was hoping to add the AFR. Although I got it all working, it would crash often. I tracked it down the way I was capturing rpm - by using the coil negative. I was getting some sort of noise, either RF from the spark plugs or maybe back EMF from the coil or something. I could figure it out and it made the project unstable. 

Roll forward a few years. I ran across some info on this and found a reference to someone having a similar problem. They solved it by making sure the ground from the coil negative interface circuit went back to the battery, not the circuit board as the voltage spikes from the coil collapse and subsequent ringing would cause the processor to crash. 

I wanted to play around with this, but I didn't want to do it on the bike. So I thought I would create test bed for running ignitions. 

I came up with an Arduino that drives a DC motor. The motor is connected to a shaft that has a taper bored in one end to simulate the end of the cam. On the other end I mounted a magnet on a cross shaft. A hall effect sensor triggers when the magnet goes by and I use this to determine "TDC". I then cobbled together a couple of stock Lucas 17M6 coils, plugs, a motorcycle battery (as I need about 3W of 12V to drive the ignitions) and my trusty Tektronix TDS2024 scope. 

I ended up using a circuit published by MegaSquirt for ignition pickup - basically using a 1N4001 and a 4N32 (optocoupler). It’s simple but seems to work pretty well. I used a simplified version of this circuit  (no “John” Zener, no C31, C11 or C12. I may add the C11 and C12 in as I do get a bit of noise):

This circuit seems to work well. I think the key is making sure XG1goes back to the battery, not to the ground plane the uC uses  (i.e. don't jumper to XG2).

​The basic procedure is to mount an ignition, set it up so the spark happens before the magnet triggers the hall effect sensor and run a program I wrote on the Arduino. The program uses PWM to increase the motor speed by 1 (the Arduino allows 255 steps) and then determine the rpms and the amount of time between the spark event and the TDC event. This is converted to an angle and is the advance. By running from around 600 rpm to 6000 rpm and taking advance measurements, you can plot the curve. 

I happen to have a small collection of ignitions I've collected over the years. A Boyer MicroMKII, an Old Britts PowerArc,  an older and newer Trispark, and an ancient Lucas AB11. I have a decent AAU, but setting it up was a pain so I didn't test it.

​A note about the reported values. The RPMs are crankshaft RPMs. The Advance angles are crank angles. You also must realize the advance angles are somewhat arbitrary as they are offset to the manufactures spec. In other words, when I run my setup I really don't know where TDC is in relation to the spark. (I didn't have an easy way to accurately determine this in the test rig.) I just set it up to be somewhere before TDC using my scope to verify. After the test run, I take the raw data and look for a "calibration" point - i.e. I know the ignition should be set to 28 degrees BTDC at 3500 rpm. So I simply find my closest 3500 rpm point, calculate how "off" my raw number is from the spec and then subtract that from my raw data. This seems to work pretty well. 

HOWEVER - as DynoDave would probably point out, it's more meaningful probably to use cam shaft angles and absolute advance data. This effectively eliminates this attempt at aligning the advance with TDC. 

Here's the data I used to set this up:
Lucas 31 degrees @ 5000 rpm
Boyer  31 degrees @ 5000 rpm
Trispark  28 degrees @ 3500 rpm
PowerArc  35 degrees @ 3600 rpm (taken off the Old Britts Web page).

So in order of evolution:

Lucas AB11 - this is an old analog ignition. What is interesting is the coil is on - i.e. energizing - almost the entire time. The only time this isn't true is when a spark happens and it's briefly grounded to get the field to collapse. I would guess this uses the most power due to this. In the following image the yellow trace is my hall effect sensor. When it goes low, that's TDC. As you can see about 2.7ms before that on the blue trace is the coil negative line. It goes low for 0.1-0.2 ms. 

Next up is the Boyer MKIII. Another analog unit. It's coil on/off times are better, probably something like a 50% duty cycle (I forgot to take a picture). 

What's very interesting to me is the Lucas and Boyer curves are almost identical. 

I then tested two Trisparks. This is a digital ignition. I had an older one and a new one. (Apparently it was redesigned to better tolerate the heat in the timing cavity with more robust components.) They ended up with basically the same curve. You can clearly see the idle stabilization effects in the 1000 - 1500 rpm range. The Trispark seemed to manage the coil on times to minimize current load, but maintain a good spark. It seemed like they were trying to keep the on time to around 8ms. 

Last up was the Old Britts PowerArc unit. It used a completely different pick up method - optical instead of magnetic. It also used a very different approach to managing the spark. This unit actually sparked three times for each cycle. In addition the coil on times were managed for each segment of the advance curve. In this picture you can clearly see the 3 pluses in the blue trace. 

You can clearly see the digital nature of the ignition in the following graph. The increases in advance are very discrete. Since there 3 spark events per cycle, there are 3 advance curves. Four, if you count the coil on event. 

Of course, being digital means you can have more than one mapping, so Old Britts supplies a "sport" curve meant to be a bit more aggressive. 

It looks like the real difference is the 2nd and 3rd sparks are more advanced in the Sport version. ​ 

Here's an overlay of the two. Sorry about the jumbled legend ( I couldn't get Excel to sort it...)

I though it would be fun to overlay them all. I used the first spark event for the PowerArc curves, but as you can see  - it looks a bit fishy. Perhaps someone with more experience can suggest a better way to compare apples to apples.

Conclusions:

Well it's pretty clear to me which one is best. Although the analog units have been around for a long time and seem pretty reliable, they really don't offer the best curve. It's well known the Boyer has issues with low battery voltages (I even saw this during my tests when my test battery went low.). The Lucas is no longer being made so it's more of a curiosity I suppose. The PowerArc I found to be very fiddly getting it set up (i.e. getting it timed correctly and fooling around with the optical wheel). You have to set it's version of TDC to your bikes. However when you strobe it, there is no easy way to adjust this and it's very easy to be off a couple of degrees. I also found mounted on the bike, it was susceptible to kickback when starting - there is mention of a start procedure on the Old Britts site you'd better follow if you want your ankles. This leaves us with the Trispark. I think this is an awesome ignition. It's easy to install, easy to dial in, makes the bike run great, seems to have a nice curve and you get idle stabilization that literally transforms your bike. 

Here's some links to information on curves I found around the net on this:
 http://www.accessnorton.com/commando-timing-advance-curves-compiled-reva-t6488.html
 http://atlanticgreen.com/boyerexposed.htm (also has Lucas Rita!)
http://www.pazon.com/files/PDF/info1/PAZONvBOYER3.pdf
http://www.accessnorton.com/electronic-ingition-that-maintains-idle-t14273-15.html
http://www.norbsa02.freeuk.com/goffypazon.htm
http://s699.photobucket.com/user/654cc/media/boyer_graph_2.jpg.html
https://www.oldbritts.com/51_150111.html

One of the last things I had to do was weld together a tail light/license plate bracket. I had to wait for the light to show up so I could figure out the relationships. Here's what I managed. (Note the last time it was registered - 2002!)

I got the bike on Nov 1, 2015 and it's pretty much done as of this week - Aug 7, 2016. I guess that's about 10 months. Since there were long stretches where I didn't do much, I guess that's not bad. The bike turned out OK. If was planning on making this my bike I would have gone further, but I was primarily interested in spending as little as possible to get it back on the road with cafe styling. My inspiration was something like these, but they have $1,000's in custom paint and body work. Maybe next time.

Mine turned out a lot more stock looking. It runs well, and seems to drive well. I need to get it registered and do some little tweaks and adjusting.

I probably should have written this in a more realtime fashion so I can remember all the bits. Once the painting ordeal was complete, the reassembly went reasonably quickly. I had been collecting bits over the months, so I had a lot of the parts I needed once I dug in. First up was respoking the wheels. I used Buchannans SS spokes and nipples. I also stripped and polished the rims. Things turned out pretty nice.

Next up was to get the engine back in the frame - without scratching things too much! I was working by myself, so I ended up putting the engine on it's side and then lowering the frame around it. I then replaced the lower mounting bolts, turned it upright and it worked great. It was simple matter to then bolt on the transmission.

I then mounted the swing arm and set up the wheel bearings. BMW's use a tapered roller bearing stack that needs the preload set up. I'd never done this before, so it was a bit fiddly, but in the end things seemed to go together correctly. I then mounted the tires and balanced the wheels.

I had decided to make a custom battery holder from the start. I used a blanking plate supplied by Boxerworks to eliminate the stock air cleaner and in it's place, on top of the tranny, I mounted the battery. I thought it came out pretty well. I also decided to put the crank case breather inside the starter cover. I hope it doesn't spew oil in there. I wanted to use peashooter mufflers, but couldn't find any in my budget. I ended up going with Dunstall replicas. Although they didn't look exactly like what I was after, they ended up sounding great.

I went through a bit of hell with the front brakes. The original set up had the master under the tank and was actuated by a cable from the front handlebars. Since the original master was toast (rusted and pitted) and the throttle control was trashed (corroded, teeth worn, etc) I needed to replace them. I also had read this set up suffered from a lot of issues (leaking fluid under the tank, poor braking due to the cable, etc. ) that I changed to a later style. This used a handlebar mounted master and simple junction block under the tank. I also upgraded to SS lower lines. It took a bit of fiddling, but came out OK.

I then started in on the wiring. I was able to use the original harness without much modification. All that was really changed was the ignition as it had a Dyna III and aftermarket coil. (I also had to fool around with the turn signals, taillight and horn.)

I was getting close to completion. Here's a shot just before turn signals, taillight, horns, grips, etc. I had originally considered painting the body work, but frankly ran out of interest and budget. Also the original paint cleaned up well enough I decided to use it. Unfortunately, the battery color didn't work. Oh well. 

I have to wait for a few bits, so I can't start it up and try to ride it. I'm hoping the transmission (which I didn't do anything to) is OK!

Where we left this project months ago was I had managed to get the engine back together after discovering shot rod bearings. Next was to put it back in the frame and get this project to a roller. I really want some of my shop space back!  That necessitated painting the frame and other bits.  

Let me preface this - I hate painting. It's not my thing. In the end I'm kinda aiming for a decent "5 foot" finish. (You know, looks good from 5 feet away or more?)

I've always wanted to try automotive paints and thought I would give a try on the BMW. I decided to use Eastwood paints - they target the DIY market and their stuff is a good compromise between cost, east of use, quality and variety. I chose the DTM Epoxy Primer and a Single Stage Black Urethane. But first I had to build a spray booth, sand down or media blast the parts, figure out a way to mount the frame so I could get at it, and acquire some safety gear (fresh air respirator, hood, suit, etc). 

There's tons of info on the net about building you're own small booth. I went with the painters plastic over a PVC frame, cheap box fans with furnace filters, and fluorescent lights style. 

What this is really for is two fold - 1) to contain the overspray and fumes, 2) keep contaminates out of your new paint finish while it cures. This style of booth is probably just OK at both, but better than nothing. I did notice there definitely was a positive pressure as there was overspray blown out all around at the bottom of the frame and floor joint creating yet another thing to try to clean up.

Here are some various bits masked off. I think this was the most enjoyable part of the whole thing. It's clean, easy and kinda looks cool when you're done. 

Ready for paint. Turns out kinda. Well lets just say I learned a lot. The overarching problem was the fact I had too much going on in here. The parts were too close together, they were too high to paint comfortably, I had a lot of trouble getting all the sides (I had to hold and manipulate with one hand while painting with the other. I got lots of runs. I got lots of overspray. I missed some places.

​It was horrible. 

Primer on. Another mistake, don't get black primer if you're going to shoot black as a color coat. You can't see where you need to paint. I should have used a grey primer. 

I ended up sanding the primer out on the frame sections (where there were runs and stuff) and respraying. (The other pieces ended up being good enough). This would have gone great had my stupid painting hood (which inflated due to the fresh air system and pressurizing and popping up the top a good 6 inches) not collided with my fresh 2nd coat. I'll have to sand that down and touch it up tomorrow. Sheesh!

Today I started in on the wheels. They're pretty ugly. 

I need to determine hub offset. The front was easy as the hub is symmetrical and it's centered on the rim so I didn't need to measure. The rear is also apparently centered, but the hub is asymmetrical, so I decided to measure where it sits. I just laid a straight edge across the hub flange and measured the distance to the rim. Looks like about 3.5/64 or 1.4mm. 

The nipples were pretty badly corroded, so I just used the Sawzall to liberate the hubs.

If you recall, when I drained the oil out of the final drive I found a bits on the magnetic drain and a chunk of metal that was a wee bit concerning:

After reading up on airhead final drives, I realized I could remove the inner cover without disturbing the gear setup. (That anti-seize lube crap is a bitch to clean out of the splines!)

Well I found the rest of it and I was able to put Humpty Dumpty back together again - sorta. I couldn't find a parts diagram for the final drive, so I have no idea what this is, but it looks like it's supposed be a trust washer that is located at the end of the needle bearing in the center of the drive.  

You can see here there is metal smeared on the shoulder of the flange and there is some blueing from overheating visible too. 

So this drive is toast. Too bad as the bevel gears actually look very good. This was a 32/11 drive with a ratio of 2.91. It's one of the tallest rears BMW made (I guess the R100S was supposed to be a powerful long range highway cruiser.) I've decided to replace it with a used 32/10 (3.20 ratio) unit off a '73 I found on eBay. This will screw up the speedo drive ratio, but who cares? Bonus is the brake pads are included - I hope they're good enough to use. 

Not so great news in the form of lots of metal fragments stuck to the magnet when I drained the transmission oil. I didn't take a picture, but it was more crap than I'd like to see. Nothing big or or chunky, mostly dust like with thin flakes. Probably the gear faces. 

The final drive was worse. Way worse. Big chunks of metal came out, including something rather significant. This really should be rebuilt, but not by me. 

It appears Uncle Ben was not too up on maintenance. The engine, trans,final drive and tires all showed signs of lack of attention. I expect this bike was just never serviced and ridden hard.