• Welcome, Guest! We hope you enjoy the excellent technical knowledge, event information and discussions that the BMW MOA forum provides. Some forum content will be hidden from you if you remain logged out. If you want to view all content, please click the 'Log in' button above and enter your BMW MOA username and password.

    If you are not an MOA member, why not take the time to join the club, so you can enjoy posting on the forum, the BMW Owners News magazine, and all of the discounts and benefits the BMW MOA offers?

  • Beginning April 1st, and running through April 30th, there is a new 2024 BMW MOA Election discussion area within The Club section of the forum. Within this forum area is also a sticky post that provides the ground rules for participating in the Election forum area. Also, the candidates statements are provided. Please read before joining the conversation, because the rules are very specific to maintain civility.

    The Election forum is here: Election Forum

R90/6 with dual plugs

All the Dyna III is allow for indepedent timing of when each cylinder will fire during engine rotation.

Did not know that all could time each cylinder, thanks. On my soon to be new 77 R100S I will be making the decision to add a Dyna III or leave the points in. Right now I am thinking of just running points if the bike runs ok.

Wayne
 
I don't mind being corrected in the least. All I know about this is when standard ignition was used and too much throttle was cranked/loaded into the engine before the engine was up on its rpm, it would rattle. With four plugs no rattle. On my bike left coil fires bottom plugs right top plugs, wires are the same length. Figgered it couldn't hurt and it seemed to make sense. No rattle good, rattle?, bad. Don't know if air pressure/density effects the ignition/intensity of spark. Good topic for a cold winter's day. should have added, standard points, '74 R90S, 9.5 pistons, 336 cam.
 
Last edited:
When the ignition is too far advanced and spark happens before the piston is at TDC, what is that called?

If you have single plugs, spark before TDC would be called normal operation as it takes a finite length of time for the flame front to start propagating. Hence to get the full benefit of the fuel charge ignition comes before TDC. With double-plugging the flame front starts in two places and to avoid having the combustion chamber pressure trying to push the piston down against the engine rotation, the spark is retarded, most commonly to TDC.
 
All I know about this is when standard ignition was used and too much throttle was cranked/loaded into the engine before the engine was up on its rpm, it would rattle. With four plugs no rattle. On my bike left coil fires bottom plugs right top plugs, wires are the same length. Figgered it couldn't hurt and it seemed to make sense. No rattle good, rattle?, bad. Don't know if air pressure/density effects the ignition/intensity of spark. Good topic for a cold winter's day. should have added, standard points, '74 R90S, 9.5 pistons, 336 cam.

Double-plugging reduces the octane requirement of the engine. The engine was "rattling" due to an octane deficiency. Double-plugging reduced the octane level required and the rattling stopped.
 
If you have single plugs, spark before TDC would be called normal operation as it takes a finite length of time for the flame front to start propagating. Hence to get the full benefit of the fuel charge ignition comes before TDC. With double-plugging the flame front starts in two places and to avoid having the combustion chamber pressure trying to push the piston down against the engine rotation, the spark is retarded, most commonly to TDC.

I realize spark is normally advanced slightly in normal operation. But I said too far advanced. When I have accidentally timed my motor too far advanced the engine makes a distinct sound that I thought was called pinging. It's the sound of your pistons being destroyed by pre-ignition. Or at least I thought that is what it was. :dunno
 
I realize spark is normally advanced slightly in normal operation. But I said too far advanced. When I have accidentally timed my motor too far advanced the engine makes a distinct sound that I thought was called pinging. It's the sound of your pistons being destroyed by pre-ignition. Or at least I thought that is what it was. :dunno
Happy Wanderer
Timing set too far advanced does lead to pinging, knock, detonation, or whatever you want to call it; but the correct term is detonation and it is destructive. Timing advanced too far means that pressure and temperature will be rising quickly as the piston is not yet moving down increasing the volume of the cylinder. High temperature and pressure will cause pockets of fuel charge to spontaneously explode producing detonation.
My problem understanding what you have been driving at is your incorrect use of the term "pre-ignition." Pre-ignition is initiation of the combustion process before the spark occurs, caused by a hot spot in the combustion chamber.
 
Happy Wanderer
Timing set too far advanced does lead to pinging, knock, detonation, or whatever you want to call it; but the correct term is detonation and it is destructive. Timing advanced too far means that pressure and temperature will be rising quickly as the piston is not yet moving down increasing the volume of the cylinder. High temperature and pressure will cause pockets of fuel charge to spontaneously explode producing detonation.
My problem understanding what you have been driving at is your incorrect use of the term "pre-ignition." Pre-ignition is initiation of the combustion process before the spark occurs, caused by a hot spot in the combustion chamber.

Ahhhhh OK. Now I get it. My bad on pre-ignition. Thanks for explaining this. And yes, it is definitely bad all around. Bad noise. Bad thing to do to the motor. And really really bad for the pistons.
 
The four plugs in a double-plugged engine all fire at the same time because the ignition system has two dual-output coils that are connected in series.
True, but every 180 degrees, all four sparks can be at a different time than all four previous sparks, because of the extra pick up. Points only open once every 360, but there are two pick up coils (at least in my Dyna III in my 71 R75/5).
The plugs are not in series.
Yes they are, on each side. Each so-called Dyna ignition coil is a true transformer with a complete primary and secondary winding.

The two 6 volt windings are in series, of course. I think we all understand that much. That means all four plugs MUST fire at the exact same time, on each fire, just as you say. But every other time can be a lot different timing for the group of four compared to the previous group of four, because of the different pickup coil used each 180 degrees of the cam.

But for the HV secondary of the transformer (stick on either side of the engine, left or right only, for my below explanation, assuming one Dyna coil is for the left and the other is for the right side):

The HV (transformer output) path is from the secondary coil output to the top spark plug wire, through the spark gap then to ground (the head) and then the bottom plug ground then back through the plug gap of the bottom spark plug wire back to the other secondary wire of the same coil (transformer).

Don't let the fact that it uses the head (ground) for a piece of wire be confusing. It's being used as no more than a wire.

If you ground out either the bottom or the top plug with a dead short, the opposite plug will get the FULL voltage from the ignition coil (transformer).

Same for opposite side of bike, of course. But you can take both plugs out and run a wire between the threads of the plugs and both will fire normally. NO GROUND IS NEEDED!!! It's a complete circuit without anything in the secondary circuit grounded. Again, it only uses the head for a piece of wire, not for a ground. A true transformer does NOT need a ground in the same ways as an auto-transformer (the stock coils).

The stock BMW coils (auto-transformers) need a ground to complete the circuit back to the ignition coil. A Dyna Coil (true transformer, not an auto-transformer) needs no ground at all, so it conveniently uses the head itself as a wire to complete the circuit to the opposite plug for that same side of the engine.

-Don- SF, CA
 
A picture is worth a thousand words

This may help. It is out of the instruction manual of my Dyna III ignition. It shows a sensor plate with two pickups. Two coils, each one with dual outputs for the plugs. A jumper between the coils for the common connection, and two trigger wires, one for each coil. I assume that since each coil has a trigger wire, and there are two pickup sensors, than the two coils are not in series. Of course, the internal windings of each coil is in series and the two plugs that each coil fires would be in series, but not the coils themselves. I have been wrong in the past, but if my memory serves me right, I never could get the plugs to fire at the same time when I swapped one plug wire left to right, and right to left, which would also suggest that they are not in series.
 

Attachments

  • Dual Plug Dyna III.jpg
    Dual Plug Dyna III.jpg
    79.3 KB · Views: 53
Last edited:
This may help. It is out of the instruction manual of my Dyna III ignition. It shows a sensor plate with two pickups. Two coils, each one with dual outputs for the plugs. A jumper between the coils for the common connection, and two trigger wires, one for each coil. I assume that since each coil has a trigger wire, and there are two pickup sensors, than the two coils are not in series. Of course, the internal windings of each coil is in series and the two plugs that each coil fires would be in series, but not the coils themselves. I have been wrong in the past, but if my memory serves me right, I never could get the plugs to fire at the same time when I swapped one plug wire left to right, and right to left, which would also suggest that they are not in series.
Hard to tell by what that shows, but it looks like you might have the type that gets rid of the waste spark.

Mine does NOT get rid of the waste spark and doesn't have the wire that goes to the crossover wire to the ignition module.

-Don- SSF, CA
 
Don, mine also has (had since it is now sold) wasted spark, this system does not get rid of it, just gives you two circuits, one for each coil. I could tell when I timed it with one timing light I saw two timing marks, like I did with points on my R90S before it was dual plugged and had a Dyna III. That is because the timing chain gets longer as time goes on, causing incorrect timing on one side. When I reversed the plug wires so each coil fired plugs on each side of the bike I still got two marks about 1/8 apart.

When I used two timing lights, one from each coil buy on the same cylinder with swapped plug wires, I could see multiple timing marks, that is the two pairs already mentioned about 1/4 inch apart. I tried moving the pickups on the rotor plate and I could get the marks close, but never on top of each other, meaning one plug still fired first with the swapped plug wires. Thus, swapping plug wires on dual plug bikes with dual pickups is probably a waste of time since the plug that fires first would ignite the gas, the second plug would be firing too late to do anything.

Wayne
 
Don, mine also has (had since it is now sold) wasted spark, this system does not get rid of it, just gives you two circuits, one for each coil. I could tell when I timed it with one timing light I saw two timing marks, like I did with points on my R90S before it was dual plugged and had a Dyna III. That is because the timing chain gets longer as time goes on, causing incorrect timing on one side. When I reversed the plug wires so each coil fired plugs on each side of the bike I still got two marks about 1/8 apart.

When I used two timing lights, one from each coil buy on the same cylinder with swapped plug wires, I could see multiple timing marks, that is the two pairs already mentioned about 1/4 inch apart. I tried moving the pickups on the rotor plate and I could get the marks close, but never on top of each other, meaning one plug still fired first with the swapped plug wires. Thus, swapping plug wires on dual plug bikes with dual pickups is probably a waste of time since the plug that fires first would ignite the gas, the second plug would be firing too late to do anything. Wayne
I am not sure if that proved anything. You have two pickups, so it will only be matched exactly to every other firing. Have you ever checked the static timing (engine NOT running) to see if there is a spark when both valves are open on that side of the engine? That will prove a wasted spark.

Also, do you know if your Dyna coils (transformers) are six volt ignition coils or 12 volt ignition coils? If they are six volt, you have a waste spark for sure because that means both coils fire each time, as the coil primaries are then proved to be in series. But because of that wire going to the crossover wire between the coils, it could mean that is a common for two 12 volt coils and that would mean you most likely do NOT have a wasted spark. It's hard to tell for sure by your schematic because it's not showing the entire circuit, such as what that wire ("long red wire") does that goes from the Dyna box to the crossover wire between the coils.

Mine has no other wires going to the crossover wire which proves I have two six volt coils with the primaries in series which also proves I have a wasted spark.

But yours must be different for a reason and that wire from the crossover wire to the box must be doing something. My guess, unless you know for 100% certain, is those are 12 volt Dyna coils and then you most likely have no waste spark, each pick-up coil trigger only one ignition coil.

That is unlike mine where either pick-up coil triggers both ignition coils every time, firing all four plugs at once, but still can be adjusted to slightly different timing on opposite sides for the actually used spark.


-Don- SF, CA​
 
Don -

Doesn't the presence of the short cross-over wire indicate that this is a wasted spark setup? Power is going to flow to one coil, through the windings, then to the other coil, through the windings and then out to essentially ground. When the Dyna box/sensors get into position, the power will be cut and both coils will fire. It almost looks like that they are suggesting that the left coil provide spark for the left plugs with the right coil providing spark for the right plugs.

I still don't see how the Dyna III system can be anything other than wasted spark. And I've not heard of any Airhead setup that is anything but wasted spark.
 
I remember back in the day when cars had points and Heath Kit (and others) provided CDI (Capacitor Discharge Ignition) systems to give a hotter spark. I installed one on my very hard to start 74 Camaro, it helped a lot.

They worked by charging a capacitor to a much higher voltage than the normal trigger voltage provided by the points, then discharged it through the coil, thus giving the hotter spark. I assumed that is the main purpose of the Dyna, or any solid state ignition. Not to eliminate the points, but to give that hotter spark. On this diagram I see two trigger wires, one to each coil, two pickups. Nothing there suggest that they eliminated the wasted spark since the cam rotates at the same speed and the sensor would pass the pickup and provide that signal at the same speed as a set of points opening allowing the magnetic field in the coil collapse giving the spark.

With dual plugs you get two hot sparks in the engine, one on each side of the piston, shorting the burn time. Sort of like burning your candle at both ends, fuel runs out faster. This is why you have to retard the timing too, fuel burns faster and it would ping (knock) if you do not.

Am I thinking right on this?

Wayne
 
What no one has said yet there are two types of the Dyna III. Standard DYNA III (D35-1) and the DUAL DYNA III (D35-2).

Attached is out of the installation manual for the D35-1. I will Post another for the D35-2 that shows how to hook up for dual plugs for both systems.
 

Attachments

  • 2013-01-16 085755_2.jpg
    2013-01-16 085755_2.jpg
    61.9 KB · Views: 74
Don, I think you are right. After reading my own post again, and about the coils you posted, the Dyna III does eliminate the wasted spark.

I came to that conclusion by what I said, "the cam rotates at 1/2 the engine speed." If my memory serves me correctly, their was only one trigger which is used by both pickups. Since the cam rotates 180 degrees for each revolution of the engine, than it would have to have two pick ups 180 degrees apart to fire the cylinders at 360 degree intervals, which it does.

Boy, never though I would be taxing my brain so much this early in the morning. Learned something today.

Wayne
 
The Dyna III does not eliminate the wasted spark setup on Airheads, at least for the non dual plugged package. All the Dyna III is is an electronic trigger for when to collapse the field in the coils to generate the spark. Since both coils are being flooded with 12v (in on one coil, through the cross-over wire, out the second coil to ground), once the Dyna III system finds that one of the sensors is tripped, 12v to both coils will be cut and the spark to both plugs is generated. It can work no other way.

The benefit of the second pickup is to allow independent adjustment of when the spark fires every 360 deg of crank (180 deg of cam) rotation. With the original points set up, due to variations in the cam that the points ride on and other wear situations, the spark may not be at the optimum time for either cylinder. With points, you typically statically time the engine to one cylinder and generally take what you get for the other cylinder. You can still put the timing light on the left plug wire and see the results of the plug firing at each 180 degree of cam rotation. This is where you'll see the double image which can be the timing chain but it's also the minor variations in the advance unit.

The dual plug setup might be different, but I highly doubt it. Just having two pickups doesn't necessarily mean that the wasted spark is eliminated. If the coils are interconnected and being fed the same 12v in series, then the system is still wasted spark.
 
Back
Top