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Dual Plug BMW Cylinder Head

Dual Plugging the R100GS

What is dual plugging? It’s the practice of installing an additional spark plug into the cylinder head, with the goal of promoting quicker combustion and preventing detonation of the combustion charge (what most people call pinging). All sorts of wild claims for additional benefits are made as well, from wheelie popping horsepower gains and double digit mileage improvements to increased robustness (after dual plugging, you’ve got a second ignition system to fall back on in case anything goes wrong with the first one, or so the story goes). In my own case, I was looking for a reliability gain, and some additional power would be nice, but only if it didn’t sacrifice the ability of the motor to happily digest low octane third world gas.

A great deal has been written about dual plugging, with the Airheads Beemer Club’s Oak Okleshen representing perhaps the most experienced perspective. Oak was kind enough to forward a copy of his seminal paper on the subject, which provides not only an excellent introduction to dual plugging, but also dispels the myths as well. Robert Fleischer (aka Snowbum) has an extensive series of web available tech articles, some of which cover dual plugging, and that occasionally capture the pearls of wisdom cast about by Tom Cutter, another Guru that frequents the Airheads Mailing List. Ultimately, the best resource was a tech seminar given by Tom and Snowbum at the 2004 BMWMOA National Rally in Spokane (Oak was also on the agenda, but a health problem prevented his participation). During the Q&A that followed their talks I was able to get the latest story on dual plugging, and by the end had a strategy for moving ahead.

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Airhead Pushrod Tube Seal Replacement

Hey! Tired of that brown slather that drips off the bottom of your motor? The stuff that seems to be coming from the base of the cylinders? If your bike’s more than a few years old, and especially if it’s been sitting for a while, chances are your pushrod tube seals are leaking. But don’t freak out, ’cause it’s not a big job to replace them, and even the parts are reasonably priced. All you need is a spare afternoon and these instructions.

Let’s start by making a trip to the BMW dealer for some parts. You’ll need four replacement pushrod tube seals (of course), two cylinder base “O” rings, a pair of valve cover gaskets, and a pair of head gaskets. Some folks say you can reuse the head gaskets, but it’s cheap insurance to replace ’em while your in there.

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Inspecting Dell’Orto Carburetors

If you are thinking of changing to Dell’Orto carbs, there are a few inspection items that you want to be aware of. These are:

Head Spigots and Connections to Carbs

1. Be aware that you must have the appropriate sized head spigots in order to mount the 38mm Dell’Ortos. Most R-bike heads either have 32mm or 40mm intake spigots threaded into the intake side of the cylinder head. In order to mount the 38mm Dell’Ortos you must replace these spigots with the appropriate sized 38mm spigots, which were used on the R90S bikes and are still available from BMW. Remove the existing spigots with a spanner wrench after soaking them with good penetrating oil and leaving them overnight.

2. Sometimes the airbox connections need to be modified in order to securely fasten the Dell’Orto carbs. For an inexpensive custom fit, go to your local Napa auto parts store or hydraulic hose supplier and purchase a 6″ section of reinforced rubber hose (2 or 2 1/4″ I think but measure yours to be sure). Cost is cheap and you can get several sections cut from 6″ of the rubber hose.

Fuel Connections

3. When you get the Dell’Ortos, remove the fuel connection on the outside of each carb and inspect/replace the fuel filter inside. Filters normally cost $1.20 each, which is cheap insurance. Also, don’t forget to check and clean the BOTTOM fuel filters on your straight BMW petcocks, if you have them. This can be done without removing the fuel tank by simply turning off both petcocks and unscrewing the lower connection. Inside you will find a fine mesh screen that captures most of the contaminants in the fuel tank feeding to the carbs.

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Valve Settings

A couple of list members have asked me about valve setting procedures, Here’s how I go about it:

The bike should be cool. Pirsig, In Zen and the Art of Motorcycle Maintenence, writes how he gets up before dawn and sets his valves before the sun clears the horizon and hits the bike. This is a bit anal, in my opinion. The machine just needs to be cool to the touch. Allow an hour or more if this is your first time, with practice, you will get the time down to 20 minutes or so, but, for now, make it a leisurely, unhurried proceedure.

Remove the valve covers (you might want to have a pair of cover gaskets on hand as the gaskets can stick, tear or become rock-hard over time). If they are in good, clean shape, they can be left in place and reused. Have something underneath to catch the couple of tablespoons of oil that will fall out when the covers are removed.

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Valve Seat Recession – A Definitive Reply

A considerable percentage of BMW Airhead motorcycles have had various valve and/or valve seat problems, up until the 1985 models. This article will try to explain the background, and why the various problems developed, and why some have problems and some do not. Note that air-cooled motorcycles are more subject to ‘top-end’ stresses, than water cooled motorcycles.

Tetraethyl lead, TEL, is dangerous if absorbed through your skin when in pure form and much less so in diluted form, and it is a form of lead previously used extensively, highly diluted, in gasoline.  Way back when it was still in use (still is in some parts of the World) it was sold by the Ethyl Corporation, and such gasoline’s had a nickname:  Ethyl.

This compound has TWO major effects. First, in sufficiently high percentage, it can raise the octane value a fair amount, very important in WWII aircraft engines, especially those that were supercharged; some were both supercharged AND turbocharged. The original purpose for using tetraethyl lead in gasoline was specifically for raising octane. Some of those aircraft engines required 145 octane gasoline. Usage for the purpose of raising octane was carried forward for decades for cars, because it was cheaper, even when the lead was sold to the refineries expensively by the then Ethyl Corporation, than using only refining methods to increase octane. Many decades ago, premium (higher octane) gasoline’s were simply called “Ethyl”. Usually those gasoline’s had MORE TEL (Tetra Ethyl Lead). There is a lot more to this story, this is a simplified version of lead usage.

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Starting your Airhead motorcycle, including in cold weather

Cold weather starting is nearly always done, & properly so, by using 100% full choke and manipulating the throttle a bit during cranking, as the engine begins to start. Have the clutch lever at the handlebars pulled-in during the cranking to reduce loading of the starter motor by the transmission with its cold thick oil. Helps the battery too.

Many manuals, including the factory Owners Manuals will say to not touch the throttle. In my experience, that is wrong. I have found that most Airheads require some throttle manipulation upon starting in cold weather, and often in mild weather.

As soon as the engine is running, reduce the amount of choke as soon as you can, yet if you need to, and you likely will, keep ‘some’ choke on, until you have smooth running, including when riding.  Too quick a reduction may result in the engine dying and needing a restart.  Typically the choke lever is returned to ~half-way within half a minute. Even in the coldest weather, the choke lever should be returnable within a few minutes to the half-way position, and not long after to full off …or, nearly so. For very cold weather, try to keep the rpm between 1200-1500 during non-moving time until some decent warmup is had.

Never blip the throttle to high rpm when starting, this is particularly very bad with a cold engine and wear will be high.  In some situations you can break rings or collapse an oil filter with a quite cold engine. Generally, you can start an engine & take off modestly, using quite moderate rpm, after 30 seconds to 2 minutes of high idle rpm (1200-1500), if the temperature is down to as low as 40°F or so.  I suggest using modest throttle when taking off, and not going over 4500 rpm, preferably not over 4000, until the engine is warmed some, which takes a couple of minutes.  

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Rocker arms, shafts, bushings/bearings. Rocker arm breakage. Valve gear. Pushrod tubes. Various parts of the cylinder heads

BREAKAGE OF ROCKER ARMS:

This is a rare occurrence, usually happens under racing conditions, with very high rpm, and/or high lift cams, increased valve spring strength, insufficient spring clearance at maximum lift, etc. However, it did happen, but rarely, on stock early Airheads, in non-racing use, and only in the /7 era, as far as I know. If you look closely at a rocker arm, immediately next to where the ADJUSTOR screws into the rocker arm, the web width there on the suspect rocker arms is about 7 mm wide. BMW made a production change and the rockers with the factory change had a 11 mm width. There was no change in the rocker part number. It does not appear to be a formal re-call by the Factory. I am not listing all the rocker part numbers, except two, because:
1. No new rockers are available that are 7 mm.
2. It is easy to confuse yourself over the SEVERAL part numbers used for the rockers. The original part numbers, long gone now, were 11-33-1-262-403 and -404.
3. You can measure your rockers.

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Replacing Rear Main Seal – 2 (Floyd)

>>Oh, no! I noticed oil running (drooling?) out behind the trans. If my diagnosis is correct, what seal is it?

I presume that when you say “behind” the trans, you mean at the trans-case interface? If you mean literally “behind” it, as in out from the boot at the trans output, you can stop reading. If not, you more than likely have a rear main seal failure. That’s the seal where the crankshaft emerges from the case to marry the flywheel.

Tools?
Pitfalls to avoid?
Tips?
Other items to replace or rehab at the same time?

With the bike now up on an elevated table (we call it the “surgery table”) and with the final drive, etal all the way off, it would be a shame to take it to the dealer. Plus the $$$$$ consideration.

Then this is the IDEAL time to do it. You have to pull off the final drive to pull the trans anyway, and that is a big part of the labor. You will need a few special tools… a flywheel holder (holds it in place so you can unbolt and later bolt the flywheel to the crank), a set of three ( I think) longish metric *fine* bolts for backing off the clutch’s diaphragm spring, and finally a tool for seating the new seal to the correct depth.

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Replacing Rear Main Seal – 1 (Garcia)

n Wednesday I decided to start a project I have put off for months. My 1978 BMW R80/7 had been leaking oil, and I suspected the rear main seal to be the cause. At first the leak was barely noticeable, but grew worse as the months progressed. I called several different shops to find out how much it would cost to replace the seal, and was quoted on average three-hundred and fifty dollars. I had worked as an apprentice mechanic at a motorcycle repair shop in Santa Barbara, CA., under the expert tutelage of master mechanic John Ireland, but I had never tackled anything so extensive on my own. I realized, though, that if I did not deal with the oil leak soon, the clutch could be ruined.

I did not want to pay for a new clutch as well as a new oil seal, so with tremendous amounts of anxiety and trepidation, I began the project by reading about the procedure in my Haynes workshop manual. I concentrated on the parts that did I did not understand, and attempted to visualize the sequence from beginning to end. Next I cleaned the garage and made sure all of my tools were in proper order. I found lots of newspaper, rags, and some cardboard boxes for parts storage. All of this preparation was crucial, since I had recently moved, and was not used to my new garage.

I missed the workshop I had built at my old house, where I had the luxury of space and light. Now I was in a cramped garage with poor lighting, so I would have to adapt. I discovered that I would have to disassemble many of the major components of the bike, as well as buy or fabricate some of the special tools that would be necessary for the job. This seemed daunting, especially since I do not have a compressor, a grinder, or a bench on which to work on the bike. Nonetheless, I started with the basics. I knew that if I kept focused, patient, and creative, the job could be successful.

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Reducing Valve Noise

This is a fairly common complaint. Could be from a couple of sources:

There may be excessive up and down play in the rocker arm assembly. Especially on the /5s and /6s where they don’t have any self-centering rocker arm mounting posts. With time, they can get loose and noisy. When you torque the heads, prior to setting the valves, loosen one set of nuts that secure a rocker arm to the mounting posts. Use a large set of channel lock (water pump pliers) or a C-clamp with two sockets and firmly but not REAL tightly squeeze the assembly together whilst tightening the two nuts. Torque those two nuts to the recommended torque. Repeat with the other side and torque the two nuts at 6 o’clock and 12 o’clock as well. Set valves on that side, go to the other side and repeat. Still have the noise?

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