Contents
I replaced all the engine electrical components and wiring and you can read about that work here:
Condition of ATU and Original Dyna III Ignition
When I removed the engine electrical components, I found the points housing was heavily corroded and the timing advance unit, also know as the automatic timing unit (ATU), was also corroded and rusty. It looked like water got inside the points housing and sat for awhile.
Oil and Corrosion Around Automatic Timing Unit (ATU)
Points Housing Full of Crud
ATU is Rusty
The bike has a Dyna III electronic ignition installed. The Dyan III uses a sleeve with a magnet that mounts on the ATU cam tube. It interfered with the left pickup scoring the sleeve and left aluminum shavings on the pickup mounted on the pickup plate. Also, the pickup plate is corroded. The Dyan III instructions caution that if water gets inside the points housing, it can damage the printed circuit traces on the back of the pickup plate.
Dyna III Magnetic Rotor Shows Abrasion From Left Pickup Magnet
Aluminum Shavings on Left Pickup Magnet
Back of Dyna III Points Plate is Corroded
I disassemble and refurbish the ATU to get rid of the rust and install new advance springs as the original ones are rusty.
The Dyna III electronic ignition uses the stock ATU but has it’s own pickup plate that replaces the stock points plate. It’s easy to install the stock points plate and points should the Dyna III fail at some point. That’s an advantage to this design. I decide to replace the Dyna III completely with a new unit.
Parts List
These are the parts needed for this work. The tension springs are what is know as the “softer” springs. This means full advance occurs a bit earlier than with the older “Heavy Duty” springs (part# 12 11 1 357 546) which are still available.
| Part # | Description | Qty |
| Dyna-D35-1 | Dyna III Electronic Ignition for BMW R 1970-1978: Euro Motoelectrics | 1 |
| 12 11 1 357 627 | TENSION SPRING (to 09/78) | 2 |
Disassemble Automatic Timing Unit
The original Dyna III sleeve is secured to the ATU cam with two set screws. For the stock ATU, this sleeve would not be there, but all the other parts of the ATU would be.
ATU with Dyna III Trigger Magnet Sleeve Mounted to Advance Cam
I remove the Dyna III sleeve from the ATU camshaft.
Old Dyna III Trigger Magnet Sleeve Removed From Advance Cam
The ATU centrifugal advance arms are mounted on a pin, secured with a C-clip.
C-clip Secures Centrifugal Advance Weight Arm On Post
After removing the C-clip, I use a screw driver to gently pry the advance arms off their posts. I have to twist the arms outward a bit so they come free from the cutout they abut on the top of the cam sleeve assembly.
Removing Centrifugal Advance Weight Arm From Post
There is a fiber washer underneath the arms.
Centrifugal Advance Weight Arm Removed From Center Plate Showing Fiber Washer
Centrifugal Advance Arms Removed Showing Advance Cam Assembly On Top of Center Plate
I use a small screw driver to push the advance return springs off the posts. These are very small and hard to find if they wander off, DAMHIK. 🙂
Removing ATU Advance Spring From Camshaft Plate Post
ATU Advance Spring
Here is how the camshaft assembly mounts in the center plate.
Removing Cam Shaft Assembly from Center Plate
Here are the main parts of the ATU; top is the camshaft assembly, below it is the center plate it mounts in, on the left and right are the centrifugal advance arms.
ATU Main Components Disassembled
Remove Rust From ATU and Clean
I soak the ATU parts in Evapo-Rust over night.
Removing ATU Rust by Soaking in Evapo-Rust Over Night
The parts come out blackened. I use steel wool to remove the black residue. Then I wire brush the parts with a stainless steel brush, apply Auto-Sol metal cleaner and scrub with a toothbrush. I apply Auto-Sol metal polish and buff with a blue shop towel. The parts look much better and the rust all gone.
Cleaned and Polished ATU Components
Reduce ATU Full Advance
Since this engine has heads with dual plugs, the ignition timing changes from the stock settings. Since there are two flame fronts expanding across the cylinder it takes less time to burn the mixture. This bike has the 6 Deg “S” timing mark with a line above and below the “S” mark. These lines are 3 Deg from the “S” mark so the top line is 3 Deg BTDC and the bottom line is 9 Deg BTDC.
Tom Cutter at Rubber Chicken Racing Garage advises retarding the timing at idle by 3-4 Deg, so I can use the line above the “S” to set timing at idle. The stock advance range is 28-29 Deg and that should be restricted to 24-25 Deg of range which reducs the range by 3-4 Deg.
Here are the stock and revised timing settings for my bike with dual plug heads.
My R100 Stock Settings
“S” on My Flywheel: 6 Deg BTDC
Advance Range: 28-29 Deg BTDC
Full Advance: 34-35 Deg BTDC
My R100 Dual Plug Settings
Line Above “S” 3 Deg BTDC
Advance Range: 24-25 Deg BTDC
Full Advance: 27-28 Deg BTDC
Tom told me he reduces the advance range by installing old advance springs over the pins of the cam assembly plate. The thickness of the springs reduces the advance range by about 4 degrees. Since I bought new return springs, I’ll use the old ones the same way.
But, I’m curious about how much thicker the pins on the center plate have to be to reduce the movement of the cam by 4 degrees. As shown below, the pin on the top of the cam assembly moves across the diameter of the large hole in the top plate. So, the diameter of the large hole represents 28-29 degrees of timing advance.
Pin on Cam Assembly Plate Fits Inside Hole in Center Plate
I measure the hole in the top plate and it’s close to 1/4″ or 0.250″. The diameter of the pin is 3 mm or 0.118″. Therefore the total distance the pin can move across the hole is 0.250-0.118 or 0.132″. If that much movement results in 29 degrees of timing advance at full advance, then each degree of advance is 0.132/29 or 0.004″. Now if the full advance needs to be reduced by 4 degrees, then the distance the pin moves in the hole has to be reduced by 0.004 x 4 or 0.016″.
When I measured the wire thickness of the return spring, it’s 0.016″ +/-. How cool that the advance spring wire is just the right thickness to reduce the full advance of the ATU by exactly what is required.
I clip off the loop on one end of a spring with wire cutters. Then I can grab the loop on the other end with pliers and pull the spring over the pin of the cam plate. It’s a tight fit.
Advance Spring Loop Cut Off on One End of Advance Spring (Spring on Left)
Installing Old Advance Spring on Cam Sleeve Pin
When I get the spring past the groove in the pin, I clip off the other loop with wire cutters. I test fit the cam in the holes of the top plate and adjust the position of the spring so it bumps against the inside of the hole. I remove the cam sleeve and put a drop of super glue on each spring to ensure they don’t slip. The coils are quite tight on the posts, but I figure some insurance is a good idea.
Old Advance Springs Installed on Cam Plate Pins to Limit Full Advance
Assemble ATU
I assemble all the parts of the ATU; as they say “Assembly is the reverse of disassembly.”.
First, I install the fiber washers, then the advance weight arms–and per the Dyna III instructions, the metal straps are creased in the middle–and then the C-clip is installed to secure the advance weight arms on their pins. Last, I use a small screw driver to push the ends of the new advance springs into the grooves on the pins.
Fiber Washers Installed on Advance Weight Arm Pins
Advance Weight Arms On Pins and Under Metal Straps
Slight Dent in Straps Over Arms and C-clip Installed on Pin
ATU Assembled and No Longer Rusty
Add New Seal to Points Housing, Drill Drain Hole
To help keep water out of the points housing, I add a new seal strip to the groove in the points housing. I put a dab of silicone seal at the two ends and at the sharp corners at the bottom. Then I trim the excess off with wire cutters.
Install New Points Housing Seal
I also drill a small drain hole at the bottom of the housing so should water get inside, it will drain out and not corrode the Dyna III pickup plate.
Drilling Drain Hole in Bottom of Points Housing
Drain Hole in Bottom of Points Housing
Installing Dyna III Electronic Ignition-ATU Cam Sleeve and Pickup Plate
Here are the components of the Dyna III electronic ignition I purchased from Euro Motoelectrics.
Dyna III Electronic Ignition Components
The black box at the top left is the electronic ignition module. I don’t install it now but will do that when I install the main wiring harness and the coils. I install the pickup plate at the top right and the sleeve with the magnets at the lower right next to the ATU.
The sleeve has a bushing on one side. This goes next to the advance weight arms when the sleeve is slid on the ATU cam sleeve.
Bushing on Dyna III Sleeve
There is a “D” shape to the hole in the ATU cam sleeve. You can see it at the 5:30 position in the picture below.
Orientation of Flat of the “D” – At 5:30 Position of Hole
The Dyna III sleeve is oriented so the two set screws are on either side of the flat of the “D” shaped hole. I position it so the set screws are about equidistant on either side of the flat and tighten the set screws. In the picture below the Allen Wrench is about even with the center of the flat of the “D” shaped hole (I tilted the wrench a bit when I shot the picture). The two set screws need to be snug, but I don’t over tighten them or I’ll dent the ATU cam making it unusable with the stock points.
Flat on ATU Cam is Centered Between Set Screws
Filing Lower Slot of Pickup Plate To Allow Full Adjustment
As I tested installation of the pickup plate, I noticed that the bottom slot in the pickup plate was not wide enough to allow full rotation of the plate in the clockwise direction. I filled the hole on one side until I get full plate rotation.
Pickup Plate Rotates Fully Counterclockwise
Pickup Plate Doesn’t Rotate Fully Clockwise
Pickup Plate Rotates Fully Clockwise After Enlarging Bottom Hole
The wires of the pickup plate don’t have the tough outer sleeve that is used on the stock points wire. The sleeve protects the wires from chaffing when the metal clamp on the bottom plate screw is secured over the wires. Out an abundance of caution, I put some heat shrink tubing on each wire where they will be clamped and cover them both with a larger diameter of heat shrink tubing. The last thing I want is a frayed wire under the clamp cause problems on a dark and stormy night 🙂
Adding First Shrink Tubing
Adding Second Shrink Tubing
I route the red and white pickup wires through the black tubing, route them behind the diode board. I push them though the “D” grommet and orient them so they are behind the large engine electric harness.
Routing Pickup Wire Through Rubber Sleeve
Routing Pickup Wires Behind Diode Board
Routing Pickup Wires Through “D” Grommet
Pickup Wires Behind Engine Wire Harness
I like to replace the slot head screws used to secure the points plate with M4 x 10 Allen head screws. These are much easier to get to when adjusting the timing.
New Allen Head Screws To Secure Pickup Plate
To avoid water being trapped in the points housing, I drill a small hole at the bottom so it can drain out should the grommet on the rubber points wire tube or the edge seal fail.
Drilling Small Drain Hole in Bottom of Points Housing
Location of Small Drain Hole
Here’s the Dyna III sleeve with magnet and pickup plate mounted in the points housing. From this angle, it look just like the stock points assembly.
New Dyna III Sleeve and Pickup Plate Installed in Points Housing
Aloha Brook!
I have exactly the same assembly on my ’78 R100/7. Unfortunately the paperwork is long-gone and Dynatek has yet to respond to my query concerning maintenance and product capability.
It seems to be a maintenance-free system which standardizes the timing and increases the voltage through the coils. But I am wondering if there is anything to be done maintenance-wise to the Automatic Timing Unit? Anything to lube, for instance, like the felt in the now gone contact points? I will be ordering some extra of those small springs for my back-up parts that I always carry with me …
Also the stock coils are being used on mine but I read on the website that the coils should have at least 3 volts running through but hopefully 5 volts. Do you recommend alternate coils and which please?
Your photo-journal so much puts my mind at ease as I know what to expect when I recondition my ignition.
Thank-you again!
Hi Matt,
Yes, it’s pretty maintenance free.
If water gets inside the points enclosure (leaking enclosure gasket and/or badly seating, missing cable seal) the back of the hall effect sensor (the round plate that replaces the mechanical points) can corrode on the backside. Contact of the backside of the round plate to the engine block provides the ground, so corrosion there is the source of weird problems.
No lubrication is required since there is no physical contact between the rotating cylinder with the magnet that mounts on the end of the cam shaft and anything else.
For a dual plug ignition system, you get better performance if you run a spark plug wire from each coil to each cylinder. That said, it works fine if you don’t do that.
I’m glad the material has been helpful to you in keeping another airhead on the road. 🙂
Best.
Brook.
Brook, this was a wonderfully clear and well documented procedure. I only wish it went farther!!! I have a 1975 R90/6 so it’s much like yours in terms of lay out. I installed the Dyna III system on the bike and all went according to the book UNTIL I hit the connections with the two coils. The problem is that the wiring of my coils was not like the wiring in the instruction sheet. I know a coil has an inner coil and an outer one, the inner provides the spark, however I’m not sure what wires go where. The diagram with the Dyna says to put the brown wire to the right coil where the old condenser went, that’s easy. But then it says to put the red wire to the left coil where the 12 volts from the ignition switch is. Ok, HOWEVER, the point to where the ignition wire goes to the coil has only that ONE led. The other, which has a blank and the crossover led to the left coil and the instructions specifically state to NOT attach the red wire to the terminal with the crossover wire. In order to make this happen, I would have to take the crossover led and move it to the terminal with only one attachment point and then move the ignition line to the other terminal point of the same coil (the left one) thus freeing up the two contact terminal in order to attach the red wire from the Dyna black box and the ignition line to the same terminal. Is this ok to do? Each coil has two terminals and of course a central line to the plug it serves. I don’t know how the two outer terminals interact, but it seems clear to me that the Dyna folks do NOT want the red line attached to a terminal that also carries the crossover line. Thoughts? Hal
Hi Hal,
This document has a clear wiring diagram for the twin coils when installing a Dyna III ignition on an airhead.
http://www.powercommander.com/downloads/Support-Released/Dynatek/Manuals/D35-1.pdf
I hope this helps.
Best.
Brook Reams.
dynatek removed all the documents as I get a 404 error when trying the link above , anyone have another link , also can’t reach them they don’t call back after leaving messages .
go to euromotoelectrics technical tips, i am reinstalling a 20 year old dyna II on my 60/5, thank you for the great write-up Brook.
https://www.euromotoelectrics.com/Dyna-III-p/dyna-d35-1.htm
Brook, i was looking at the dyna III that a local airhead specialist installed on my r90s and it appears upside down from your install, the wires come out of the top of the back plate and out the cutout. I am wondering if i need to splice in some wire and rotate the unit 180 degrees?
best,
Andrew
Hi Andrew,
As the old saying goes, “If it ain’t broke, don’t fix it.” As long as the wires aren’t under strain, don’t contact the centrifugal weights, and you can adjust the points, it’s all good IMHO.
Best.
Brook.
Brook,
after inspecting it more closely, and removing it, it looks to be put on correctly, as the screw holes are at 11 and 6 oclock, if i were to rotate 180 degrees they would not be close to alignment.
I am rebuilding the engine after a broken rod punched a whole in my crank case. I attributed it to that piston firing in advance or some unknown problem related to a recent one over bore and piston job.
I had minor vibrations on that side of the bike prior to failure, but i attributed it to a carb issue, so i rebuilt the carbs, and learned to test the del orto double pump diaphram.. got the carbs all dialed in to the best of my ability. this work seemed to improve the performance but never removed the vibration i was feeling.
then the failure….
after reading this article, i inspected the ATU more closely, i have ignored it up until now thinking the dyna iii makes the whole timing thing “maintenance free”. the atu springs are horrible. one is much worse than the other.
i now attribute my failure to the springs, or an improper adjustment of the dyna iii which caused the advanced firing on one side…
either way, the whole thing could have been avoided with a timing gun and some self confidence….
like many, i figured anything done by a mechanic was better than what i could do, and so i avoided revisiting areas of the bike i paid to have worked on…
i now have learned it is my bike and no one is going to fix it better than me…
thanks again for all you do.
best,
andrew
Hi Andrew,
I’m sorry to hear about the connecting rod failure.
The ignition system always fires both spark plugs at the same time and that’s why it’s sometimes referred to as a wasted, or lost spark, ignition system. Consequently, there is no asymmetric behavior that would affect one cylinder more than the other.
Based on your description of the work done on the bike, I would tend toward something having gone amiss when the bore out was done rather than ignition timing as the cause of the broken connecting rod. The vibration could be due to incorrectly sized connecting rod bearings or not reaming the wrist pin bushing correctly. If either of those connections are too loose, the connecting rod slams into the crankshaft (rod bearing), or the wrist pin (bushing),. Over time, those slamming forces will break something if allowed to go on long enough. But that’s just my amateur opinion.
Best.
Brook.
thank you for your suggestion. you are probably right. i have learned a valuable albeit expensive lesson.
best,
Andrew
Andrew,
Alas, that’s how I learn as well. 🙂
Best.
Brook.
Hey Brook,
Fantastic write up and pics as usual!
Just jumping onto this thread for (hopefully) some simple advice. I have the Dyna III fitted to my 1978 R100/7 (it was installed when I bought the bike and assuming it’s been on a few years already). The bike runs fairly well but I have a noticeably weak spark on one side. I have swapped the coils, with leads and plugs over and the weak spark remains on the same side – I am wondering if the dyna III could be causing this? Or any other ideas on a root cause?
I noticed above you mentioned the sparks fire together (wasted spark point) so would it be possible to bridge a connection (the strong one) leading out of the Dyna III?
Jordan,
I have had Dyna III units fail. If the coils, plug wires and plugs all test okay, that leaves the Dyna III unit itself as potentially failing.
A test for that is to remove it and use the stock points & condenser. Then see if you weak spark continues or not.
I hope that helps.
Best.
Brook.
Thanks brook,
Since the message I ordered new plugs, coils, Dyna III ignition and condenser from Euro MotoElectrics, installed everything and still a weak spark on the right. I am happy I replaced the components as the ones on could have been very old but obviously frustrated not to have fixed the initial issue!
I followed your instructions for the Dyna III and the other bits are pretty simple but still no solution.
Jordan,
That’s frustrating. Is there any chance you can install the original points without the Dyna III to see if the problem persists?
How do you know the spark is weak on the right side?
I’m out of ideas at the moment.
Best.
Brook.
Hi Brook,
Me too! I do not have the original points unfortunately to test. The spark is visibly smaller/weaker – I would say it’s only 20% of the spark on the left.
I took a video if it’s possible to send?
With new plugs, coils, ignition and condenser, along with switching the leads I am also out of ideas.
I’ve swapped the Dyna new and old Dyna back and forth and no difference.
Hi Brook , one question on the install. When you put the rotor on the ATU shaft the instructions say to “straddle the flat spot on the shaft with the set screws of the rotor” If you are looking down the shaft with the flat spot at bottom would the set screws on the rotor be at the top or the bottom in regard to the flat spot?
David,
I believe I put the set screw in the center of the flat spot.
Best.
Brook.