Dyna III Ignition installation; lousy tech writers!?

Continuing the R90/6 rebuild/upgrade. Installed a Mac deep sump oil pan today and started on installing a Dyna III ignition. The problem I am am having is two fold however. First, the installation instructions concerning installing the "donut" on the stock advance mechanism appears to be too vague. Does anyone know of a better or more comprehensive guide to installing it on an airhead. As far as tech writing goes it really leaves a lot to be desired. It talks of manipulating the "bosses" that hold the weights in place (?). Maybe I need to sleep on it but it appears really unclear. Insight for the slow witted would be appreciated.

Secondly, the stock advance mechanism appears to be about the flimsiest POS I have seen yet. I have replaced the springs once before but lately it has been "coasting" because it won't return from advance. Doesn't anybody make something better that doesn't look like it was made out of compressed rust and soda cans?

I have also included a picture of the new Mac deep sump. First impression? It is very robust and I seriously doubt that a piece of road gravel going 70mph is going to poke a hole in it but it is ugly and looks like it may drag. Anybody got any ideas about a bash plate/engine guard?

banzaibob said:

Does anyone know of a better or more comprehensive guide to installing it on an airhead. As far as tech writing goes it really leaves a lot to be desired. It talks of manipulating the "bosses" that hold the weights in place (?).

Secondly, the stock advance mechanism appears to be about the flimsiest POS I have seen yet. I have replaced the springs once before but lately it has been "coasting" because it won't return from advance. Doesn't anybody make something better that doesn't look like it was made out of compressed rust and soda cans?

I have also included a picture of the new Mac deep sump. First impression?

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I have always thought that the advance mechanism was completely out of character for this quality of bike. In BMW's defense though, it was no worse than that which was used on my Honda of the near-same vintage. One would think that there would be closer tolerances, as all three of mine were "sloppy."

It may be just an optical/photographic illusion, but your pan looks deeper than the used one I purchased. Did you happen to check on just how much oil it will hold up to the mating line? My was almost exactly 2 quarts. That "helped" me to understand just where on the dipstick where 2 quarts level would show up.

The deep pans that I have seen installed mostly all seem to be "banged" up. But they are so well built that they seem to fare pretty well. I still don't understand how they would get so banged up (looking like they hit a solid curb or something) on a street/highway bike!

It talks of manipulating the "bosses" that hold the weights in place (?).

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I never had to do anything like that with the Dyna III on my /7. I would say forget that information. About the only thing they could be referring to is some adjustments associated with a dual-plug installation. If you have a dual-plug setup, then yes, you will have to consider restricting or altering the advance curve. Snowbum discusses that on his website.

Otherwise, the placement of the donut is trial and error. I just went through a round of adjustment to my timing...I'm still not there and have to go back and recheck. Since you have two coil pickups (as you look at the front of the engine, the left coil is for the cylinder on your left, and the right coil is for the cylinder on the right), the small magnet in the donut needs to be approaching appropriate coil as the S-mark shows up in the window. This is where the trial and error comes in. Just study the movement and try the installation at one point. I thought the instructions provide a basic guideline for initial placement.

Also, don't crank down on the set screws for the donut. If they're too tight, they can distort the advance mechanism unit itself which screws up how it operates. Reasonably tight should be fine...use blue Loctite if you need to.

The advance mechanism on points equipped airheads was about as good as any of that vintage. Virtually every car with a points equipped distributor had a very similar advance mechanism buried down in the distrubutor below the points plate. It was out of sight - out of mind - and difficult to service. BMW put it out front, easy to access, easy to clean, easy to lubricate, and in the way when setting points gap. Even the more modern "points in a can" setup in the '79-'80 era had a mechanical advance mechanism with springs and weights. Like cars of the time hard to access, hard to service but out of sight, out of mind.

PGlaves said:

The advance mechanism on points equipped airheads was about as good as any of that vintage. Virtually every car with a points equipped distributor had a very similar advance mechanism buried down in the distrubutor below the points plate. It was out of sight - out of mind - and difficult to service. BMW put it out front, easy to access, easy to clean, easy to lubricate, and in the way when setting points gap. Even the more modern "points in a can" setup in the '79-'80 era had a mechanical advance mechanism with springs and weights. Like cars of the time hard to access, hard to service but out of sight, out of mind.

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And, to be honest, seemed to work pretty well.

jimmylee said:

And, to be honest, seemed to work pretty well.

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Indeed they did!

The donut has 2 set screws which, when screwed in equally, will allow a little wobble in each direction. Tighten them equally until that rotation is equal, then continue until everything is snug. At least that's how I did it and it worked pretty well.

PGlaves said:

Indeed they did!

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The only trouble I ever had was on my R90/6. The cam lobes were not exactly 180 Deg. apart. Hence, one cylinder timed perfectly, and the other was about 2 Deg. off. I had to "polish" with an ultra fine machinist's hone, the higher lobe so that in the final process, both lobes broke the contact points at exactly the same time so that both cylinders were at least timed with each other. I didn't change the height of the cam lobe so I could keep the duration the same. I just hit the spot where the points just began to ride up on the lobe.

Smoothed it out a little.

One of the big problems was that the installation instructions were printed with such low quality that words like "send" came out looking like "sand." "Bend"="band," etc., etc. I was eventually to get the two set screws on the "donut" to properly line up with the "D" on the advance through the process of elimination.

Another problem was the the retaining screws on the pickup plate were not quite where they should've been. I had to open them both toward the center a little bit in order to make sure the mounting screws didn't drag therefore limiting adjustability. I was able to do the static tune and now I get a big blue spark right on "S".

Aren't there heavier advance springs available?

jforgo said:

Aren't there heavier advance springs available?

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Other than replacing to get back to "like new" if yours are wore out, you don't want "heavier" springs. The centrifugal movement of the weights rotates the cam and affects when the spark happens - the amount of advance that is applied, until it reaches full advance (weights fully out). Heavier springs would not advance as fast, or not at all. You don't want that.

I think you may be confusing the "sloppiness" of the various parts when system is at rest for spring pressure.

I think the best thing you can do is to make sure each of the moving parts are properly lubricated at their wear points. I have always used a lithium based grease, but there may be something better. Be sure to use anything sparingly as you don't want any lube splattering around all over the place.

banzaibob said:

...the stock advance mechanism... Doesn't anybody make something better that doesn't look like it was made out of compressed rust and soda cans?

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I've used the Dyna III and the Boyer electronic ignitions- both work very well, but the Boyer eliminates the need for the mechanical advance if that is your preference or if your advance mechanism is damaged.

Using heavier spring would in effect give you a different advance curve. I had a similar problem on a Honda CB750/850 build. I was having a spark knock problem at low rpm/high load situations. Full advance on those is at 2500rpm. Heavier springs made full advance at 4500rpm, ran like hammered dog sh%$.

My main concern is that sometimes after full warm up, it tends to idle fast. Given that there are no air leaks or pilot circuit problems, that was where the problem was. I had a similar problem on this bike a couple of years ago, new springs cured it. Now it is showing tendencies again. If the frequency of failure is this great then I would think that someone would come along and invent a better mouse trap.

b-bob -

I'm really at a loss as too the issue with the springs. For the most part, they are the least trouble of the system. I've got 100K miles on my /7 and have changed the springs just once...only because I thought it might make a difference, which it didn't.

If you have a fast idle after warm up, since you have no leaks, I believe the only two things this can be are 1) the advance unit is sticking open or 2) the carb synch wasn't done on a fully warmed up engine carbs.

OK, stiffer springs could conceivably pull the weights back in, but if they're sticking open, it's best to figure out what's causing them to stick open...then should very freely move in and out. There is a downside to way stiff springs as you suggested.

The springs might not be the problem... the cam might be worn/corroded and sticking slightly (you might try cleaning and lubricating it carefully, if you have not already). Or, it might be time for a replacement advance mechanism, as they do wear over time.

20774 said:

b-bob -

I'm really at a loss as too the issue with the springs. For the most part, they are the least trouble of the system. I've got 100K miles on my /7 and have changed the springs just once...only because I thought it might make a difference, which it didn't.

If you have a fast idle after warm up, since you have no leaks, I believe the only two things this can be are 1) the advance unit is sticking open or 2) the carb synch wasn't done on a fully warmed up engine carbs.

OK, stiffer springs could conceivably pull the weights back in, but if they're sticking open, it's best to figure out what's causing them to stick open...then should very freely move in and out. There is a downside to way stiff springs as you suggested.

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Ditto!

Does anyone know at what RPM the engine is supposed to be fully advanced? I have only static timed mine to timing mark, so I am not sure how well the advancing is. My 40-year-old timing light died a couple of years ago.

jimmylee said:

Does anyone know at what RPM the engine is supposed to be fully advanced? I have only static timed mine to timing mark, so I am not sure how well the advancing is. My 40-year-old timing light died a couple of years ago.

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Check here - http://bmwmotorcycletech.info/ignitionsingleplug.htm - it's there somewhere! Snowbum says the /7 should be around 3000 RPM. The advance unit changed over time, but that's about the point for the /6/7 bikes.

I had an old timing light from Sears...it had the spring that you clipped to the end of the plug and then had to reach through to clip the light to the spring. Kind of cumbersome...I dropped it and broke it...probably the best thing I did for myself! I bought a cheaper Sears model, induction timing which has a clip that goes around the wire...much easier to put on and take off. Probably time to think about a new one! Actually, don't places like Autozone let you borrow theirs??

20774 said:

I had an old timing light from Sears...it had the spring that you clipped to the end of the plug and then had to reach through to clip the light to the spring. Kind of cumbersome...I dropped it and broke it...probably the best thing I did for myself!

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Funny you should mention Sears. Mine was also a Sears, but a pretty expensive one (40 years ago!). It looked like a "ray" gun, and you hooked the black wire to ground, and the springy clip to the exposed "spring" that they provided to go between the plug and the cap.

On my previous 2 BMWs, I made an interim metal piece that on one end, it screwed on the top of the spark plug, and the other end was made to fit into the plug wire cap. Then I would clip the hot "timing light spring clip" onto the metal piece that I had made.

That particular timing "gun" developed some sort of internal short so that, even though it still worked, it would occasionally shock me when I pulled the trigger button. Wasn't full voltage that went to the plug, but enough to make me nervous! I pitched it about 3-4 years ago when cleaning out the garage. Didn't think I would ever use it again, seeing as how the cars now are timed by the computer. Now I wish I had it back - shock and all!

I know Auto Zone does lend for free, as I borrowed the pressure gage to do a compression check. I am not sure if they offer a timing gun or not.

Jimmy -

I think I had the same style of Sears timing light...it was a long time ago. Heavy, too, as I recall. I'm not sure I'd call them guns, at least not today...more just timing lights. The inductive work differently by sensing when the pulse is going down the wire and then trigger to light to flash. Heck, I'm sure Harbor Freight has them.

http://www.harborfreight.com/timing-light-with-advance-40963.html

I'd probably pass on one with the advance mechanism built in...you just don't really need that complication. Another good feature is to use it to freeze the advance weights as they move in and out.

Therefore the problem! A Lucas mechanical advance for Brit bikes in the 70's is pretty tough. The only failure I've ever seen in those old Honda advance units are seizure from sitting for years. In contrast, I think that the BMW (Bosch?) advance looks physically wimpy and cheap. I too, would like to know when full advance is. I've got a lot of Asian centrifugal advance units laying around, it would be cool to start measuring in hopes of finding something that I could substitute.