Darryl.Richman's picture

Electrics - Part I: Ignition

In the 20s, Harley dropped the use of magnetos and went to battery/coil (Kettering system) ignition. This must have reflected increasing confidence in the capacity and capability of batteries available at the time. The Kettering system is both simpler and delivers a hotter spark at kickstarting speeds. Given a rugged and reliable battery, it is a less expensive system, but it is harder on the breaker points because of the high energy that the points must constantly interrupt.

BMW persisted with magneto ignition, at least as an option, through 1941. By 1936 and the introduction of the R5 model, BMW was turning to the battery/coil system as well, but in the 20s, BMW sourced Bosch magneto/generator combination units.

The magneto is a high tech device that provides a spark without regard to any other part of the electrics. Because it doesn't depend on a functioning generator or battery, magnetos are still in use for private aviation, where reliability trumps all else. The magneto's typical downfall -- especially with vintage units -- is the nature of the way the unit is constructed.

BMW /2 aficionados are well aware that the specially wound coil necessary is susceptible to the degradation of the shellac insulation on the very fine wire. This goes moreso for the units from the 20s, which were not even powerful enough to use the simple, distributor-less "wasted spark" arrangement that the Harley had. (A wasted spark system doesn't require a distributor mechanism to decide which cylinder needs the spark, but just fires both; one of them fires a cylinder and the other uselessly fires in a cylinder with no charge.)

An advantage for the magneto occurs with regard to the points. Because the Kettering system runs the full power of the ignition system across the points, there can be significant arcing, pitting and burning of the point surfaces when they open, and the flow of electricity comes to a sudden halt. In a magneto, the limited power induced by the rotating permanent magnet in the primary windings of the coil is what is interrupted when the points open. This is much easier on the points, and assuming that the cam follower is kept lubricated and clean, the points could last the lifetime of the engine.

As alluded to above, however, the magneto generates a spark whose intensity is proportional to the speed at which the magnet rotates. When the engine is running, this is not a problem, but when kickstarting, the magneto can produce a marginal spark (or none at all) if it isn't set up correctly or if the coil is deteriorating.

In the 2010 Cannonball, with bikes built before 1916, they all ran magnetos. There were many problems and some bikes had two or even three magneto replacements. My magneto has been completely overhauled, plus I have a spare magneto to bring with me, so I'm hoping to avoid big magneto problems.

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I saw lots of mag problems on

gusest's picture

I saw lots of mag problems on the trip. You might bring along a coil, just in case you need to "rig" a coil ignition through the points.Old HD XR-750 trick.

It's an old /2 trick, too!

Darryl.Richman's picture

Back when replacement magneto coils for the /2s weren't available or, if they were, they weren't reliable, it wasn't uncommon to put a Harley coil up under the tank. With a little bit of care, it was possible to switch over to battery/coil operation in just a few minutes.

But a magneto should follow a Gaussian distribution (a U shaped curve) for it's lifetime. There will be a significant number that experience "infant mortality", followed by a long and useful life, with failures only gradually piling up over time. Electronics and lightbulbs follow this curve. My rebuilt magneto has already seen a couple thousand miles, and it's my intention to run it much more next year, so it should be well past the infant mortality stage.

There is no doubt that a magneto failure stops you in your tracks. But replacing a mag with a spare (which I fortunately have) is so simple on the BMW that I hope to be able to survive on that.

(To replace the mag, one brings the motor to the full advance point, which I have marked on my flywheel. Remove two wires, the spark advance cable and the high tension leads. Then, a 10mm wrench loosens the hold down band and the mag slides back and out. The new mag, with its points set so they are just opening, is slid into place, the band retightened and the wires, leads and cable reconnected.)

If I should have a mag failure, my crew can find a Harley or a VW coil for me as a second backup. But the coil trick doesn't work as well with the Bosch D2 series units because the condenser is built in and not intended to take the high current that a Kettering system will put through it. It is more difficult to isolate the points from the rest of the system, and I fear that a switch to a battery/coil would probably lead to another failure that might be harder to fix on the road.

--Darryl Richman
http://darryl.crafty-fox.com
"Bling is not made in Germany" --OTL, 12/05

Looks like no coils allowed

Darryl.Richman's picture

I was just visiting the Rules page over at the Cannonball site. It reads:

Quote:

If your magneto isn't rebuilt you should consider it. We want each bike to use it's intended ignition source, spares allowed.

So, it looks like I need to get my spare magneto together and ready for use.

--Darryl Richman
http://darryl.crafty-fox.com
"Bling is not made in Germany" --OTL, 12/05

Mag Condensers

Darryl.Richman's picture

BTW, there was a very interesting pair of articles in the Fall and Winter issues of The Antique Motorcycle (the magazine of the AMCA club), in the "Three Rs" column, penned by Charles Falco (he, of the Guggenheim Art of the Motorcycle exhibit and also an experimental physicist).

In the first, there is a discussion of mag failures and the realization that the condensers, which ought to be about the most reliable part of the system, in fact have a shelf life, even if not used and stored in a cool, dry place. (This due to a change in the way they were made after WWII. The discussion was pretty specific to Lucas mags, but probably applies to any other unit as well.)

The second half of the article in the Winter issue discusses a modern replacement condenser. Actually, Falco selects a pair of capacitors that are to be soldered in parallel to achieve the correct voltage and capacitance values. Specifically, he used Panasonic 0.082 μfarrad polypropylene film capacitors (Digi-Key SKU ECQ-P4823JU). Two together in parallel yield 0.16 μf capacitance.

When soldered together, they coincidentally take up about the same space as an old fashioned folded wax paper/aluminum sandwich condenser. Actually, Falco speculates that it may not be so coincidental; the physical space may be a requirement with current materials and techniques.

Anyway, as a tech geek, I found it very interesting and maybe quite useful!

--Darryl Richman
http://darryl.crafty-fox.com
"Bling is not made in Germany" --OTL, 12/05

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Darryl.Richman's picture

More on the Harley JD Model

I thought I would just make the comparison between the JD and the R52/R62 (R62 shown) a little stronger:

I tried to get these two images correct to scale, since the bikes have nearly identical wheelbase numbers (55.6" for the JD, 1400mm/55.1" for the R62). The JD is a 1928 model, the first with a front brake.

At every point, the design choices by the two companies are interesting. For example, let's look at the front forks. Harley has a leading link design, with the heavily valenced fender moving with the suspension. Its larger tires add comfort to the ride as well as probably making the bike work better on the unpaved roads of the era. BMW's trailing link design mounts the fender on the fork, so it doesn't move with the suspension, and sufficient clearance must be provided under the fender for the full travel of the wheel. OTOH, mounting the fender on the fork reduces unsprung weight and the mass that the front spring has to control.

Or, look at the 3 speed transmissions. The BMW unit is huge relative to the Harley box (which is directly behind the starter pedal and under the battery box in the image above). Even accounting for the fact that much of the visible size of the BMW transmission is in fact a toolbox (the JD's toolbox is mounted on the forks under the lamp and the horn), the long shafts that must run longitudinally make the unit take up a lot of space. All of that length runs across the frame on the chain driven Harley.

In spite of the visually large castings on the BMW, it's 70+ lb. weight advantage is due in part to the extensive use of aluminum. BMW's double-decker heads not only transfer away a lot more heat than the unit cast Harley cylinders, but they are much lighter.

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Darryl.Richman's picture

50 Entrants Today!

The 50th entrant was added to the Cannonball roster today. Looks like there will only be the two BMWs, my '28 R52 and Jack Wells' '29 R11 (#23 ridden by Norm Nelson).

It has been pointed out that about 50% of the entrants are riding Harleys, with a majority of them on JD models. The JD was introduced in 1921 and was built through 1929. It was a development from the J model, introduced in 1915, and in the 2010 Cannonball, the 1915 Harley J models won most of the perfect scores.

The JD sidevalve engine displaces 1200cc/74 cu.in. (nominal) and has battery/coil ignition. It has a bore of 3 7/16" (about 87mm) and stroke of 4" (102mm) with a compression ratio of 3.8:1, delivering about 22hp @ 3200rpm. The combustion chamber, as with all of the sidevalves of the era, has an interesting shape due to it's "inlet over exhaust" construction. The iron cylinders were cast with integral heads.

The JD included a 3 speed hand shift transmission and a rear brake; a front brake was added in 1928. Dry weight was just over 400 lbs., and the gas tank holds 4¾ gallons. Electric lights were standard on the later models, like many of the entrants.

Although BMW has long had a reputation of being under stressed and conservative in their design, when you compare the Harley JD engine to BMW's offerings, you can see that BMW was produced a more tightly wound machine. The JD engine produces 18⅓ hp/liter, but the R52's 500ccs makes 24 hp/liter. This same ratio holds for BMW's bigger 750cc offerings in the R62 and R11 models (like Norm will be riding). Let's hope that the BMW design is conservative enough to make it nearly 4,000 miles across the US!

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Darryl.Richman's picture

Happy Thanksgiving and a 2nd BMW

Happy Thanksgiving to all!

Last night a couple more entrants were added to the Cannonball Rider's page, including Norm Nelson on a 1929 BMW R11. Unfortunately, the Rider Profile isn't filled in yet.

I don't know Norm, but a quick Google search reveals that he is involved with the BMWNEF (North East Florida). Jack Wells had previously mentioned that his bike - a 1929 R11 - would be entered as part of a team including the members of BMWNEF. I can jump to a conclusion as quickly as anyone... and be just as wrong... but I'm sure we'll know more about this soon.

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Darryl.Richman's picture

Serendipity?

When you have old bikes, even old BMWs that you want to "ride as the maker intended", you end up needing to haul them around in a 4 wheeled contrivance, sometimes more than one at a time. We have an old Toyota Tacoma that has been doing this duty for years now, but there are several drawbacks to it:

  • It's open to the elements: wind, rain;
  • It's open to the eyes of others while traveling;
  • It's a very tight fit to get two bikes into the short bed and the tailgate has to be left down; and
  • My wife uses it for her Art Glass shows, and wants the topper on it

On my trips to Germany and the vintage events there, the common solution was one of the many big panel vans available there, such as the VW Crafter, the Fiat Diabbolo or, the most common by far, the Mercedes Sprinter. Only the last is available in the US, and they are branded several ways (Mercedes, Freightliner or Dodge) because of the different ways MB is/has been hooked into the US market.

The Sprinter has a lot of advantages. Your tools and bikes are out of view and out of the weather. There's lots of room, and because of the tall box design, there's even a lot of overhead space. They get surprisingly good fuel economy.

So, I've been occasionally browsing Craigslist and eBay for one. The big disadvantage to them is that they are expensive. I found that Sprinters with 100,000 miles on them tend to get well north of $20k and those with more than 200,000 miles still get about $15k! I even saw one with over 400,000 miles asking $15k!

Well, persistence paid off, and I bought one early this year. It was advertised only in the SF Craigslist but located in Sacramento, which may have put some SF buyers off and eluded some Sacto buyers. Also, it's bright yellow!

   

So far, the only customization I've done is to add a backup camera. It made me very nervous not to be able to see anything behind me. That, and the week I bought it, Cycle Gear was having a sale on rocking front wheel chocks; there's one directly off of I-80 on the way back from Sacto, so I stopped in, bought two, and threw them in the back. I still haven't even bolted them down.

I love the Sprinter! I've driven it around California and it gets a consistent 23-24 mpg. A friend who has the longer model tells me that it doesn't matter how heavy a load you put in it, it gets the same economy. (It really only depends on how hard you put your foot in it.) With the sliding doors on either side and the rear doors that swing open around to the sides, loading and securing 2, 3, maybe even 4 old bikes is easy! (I haven't tried 4 yet, but I don't see why it would be a problem.)

Reactions to the Sprinter tend to come in two ways. One is, "Can you help me move xxx?" The other shows that everyone sees that vast expanse of yellow paint as an empty canvas needing to be filled. I've had many suggestions about what kind of graphics I should put up on the sides.

But my idea is this: I am looking for some sponsorship for this Quixotic adventure. I will put your name or your business name up on the side of my Sprinter in exchange for some support! Click on my name at the top of any of these postings and send me an email!

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