Technical Tips – Page 5 – Airheads Beemer Club

Throwout Bearing Maintenance

…cleaning, inspecting, and servicing the throwout assembly on ’74 to ’84 airheads every 10K. Would someone be willing to describe this process in enough detail so that I would have half a chance of performing this myself successfully?

Sure… The reason I suggest doing this, is due to the nature of the layout of the rollers in the bearing. Before the ’74’s (/5 and earlier), BMW used a ball bearing throw-out assembly. They went back to this after 1984. If you referrence a price list, you will see that the ’74 to’84 roller set up is a LOT cheaper. The rollors are laid out radially in a circle.This insure that as the rollers attempt to roll, one end will go faster than the other and will scrape on the two “thrust pieces” on each side.

The bearings do fail (usually indicated by a sudden need to take up slack in the clutch cable). Now, the failed bearing, the two thrust pieces and the clutch thrust rod are turning as a unit. The clutch end of the thrust rod can bore into the forward pressure plate of the clutch assembly. Surprisingly, the bike can still be operated while this is going on, with the rider noting strange shifting and odd clutch noises. This happens often enough that I carry a spare set up as insurance for my wife’s ’78 R100/7, when we tour. (I have, of course, the vastly superior /5)

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Spline lubricants

Airheads need scheduled lubrication on transmission input shaft splines (never grease the clutch disc splines themselves); and, rear wheel cup splines and associated rear drive output splines on the twin-rear-shock models.

Numerous lubricants have been tried in many different climatic and riding conditions, over many years. Some newer lubricants are still being tested. There does not seem to be any magic, perfect lubricant for these places. BMW has specified quite a few lubricants over the years, such as Staburags, Optimoly, ETC. The author has never believed these lubricants were as good as some others, at the times BMW had those recommendations. The author, and others, have done long-term testing on various lubricants. This article you are reading no longer lists these lubricants, nor recommended lubricants, as the latest information will be found HERE:
http://bmwmotorcycletech.info/chemicalsetc.htm where the author keeps the information up-to-date. The spline lubricant information is at item #6A in that article.

Later model (exact year and models are unclear, probably late 1980’s) transmission input splines are SUPPOSEDLY nickel-plated and do not require cleaning and relubrication quite as often, but 30,000 miles seems the practical LIMIT, and for earlier ones perhaps 20,000 is the limit. Best you do it before these mileages, at least once, and then, upon inspection, adjust the interval for the next clean/lube. Once a spline shows rusting, you are LOSING METAL! The transmission input splines are fine-pitch and not very deep….you do NOT want them to fail!

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Re-Gearing an R80/7

Charles Bachmann, charles_bachmann@mgv.com writes:

Hi Airheads,

I am a fairly new owner of a 1978 R80/7. It is a great, fun bike. However, I find that at speeds over about 60 mph, the thing turns higher rpm’s than I would like. I am considering going to a higher gearing.

Thanks for any feedback/advice!

Charles Bachmann
Raleigh, NC

I know how you feel. I’ll bet you’re always looking for 6th gear.

A 37/11 drive is the same that came on my ’74 R60/6. At 60 mph I’m showing at least 4000 rpm. Kinda high. But it’s only a R60. On the other hand, it’s the same drive that came on my ’83 R80RT. This was not acceptable to me. I replaced the 37/11(3.36:1) with the next higher-up 32/10 (3.20:1) from an R75/5. The drive housing has a different look & design, but everything fits fine. It was better, but still too revvy for me. Unlike you though, the ’83 R80 has lower compression than your ’78, therefore less horsepower too. I dare not try a higher drive because I have already lost a fair chunk of power.

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Clutch – Maintenance

Warning! Warning!! WARNING!!!
Under no circumstance should the flywheel or clutch carrier on any model be removed without first blocking the crankshaft from moving forward!! http://bmwmotorcycletech.info/flywheelremovalwarning.htm

You must block the crankshaft! Do not take a chance on serious damage to the engine!

Many have removed & replaced an Airhead flywheel or clutch carrier without blocking the crankshaft with no problems. My advice, very strongly given here, is to take a minor amount of time & make & use at least my simple crankshaft blocking tool. If you do not use some sort of crankshaft blocking tool, & your crankshaft should happen to move forward enough (does not take much pressure nor does it have to move far!) to have one or both of the thrust washers fall off their pins, you could cause very serious damage as you attach & bolt-up the flywheel or clutch carrier. Even if you do not cause serious damage, if the forward thrust washer drops, you may be unable to get it back on its pins without a very considerable amount of work. Do not take a chance!

Since it is a must, in my opinion, to mechanically block the crankshaft from moving forward at any time during the process of removing or replacing a flywheel (or clutch carrier as it is called on 1981+ including some 1980 models), you need to know how to best do that.

This can be done in several ways. I recommend you do not use ‘a towel’ between the front cover & the alternator rotor, as is sometimes done. I recommend a simple & neat method …just make a tool out of a piece of Allen wrench material, weld a disc (fender washer) on one end, making the length such that the Allen end fits into the alternator bolt, & the disc end presses against the inside of the outer timing chest cover. Usually 3/4 inch overall. The length should be such that there will be some light pressure applied by the cover to the tool, the cover being screwed back towards the engine lightly (but not touching the engine case). The tool should be just long enough that the cover can not be fit fully home all the way. Obviously you don’t want to tighten the outer cover very much & you do not need to!

A further treatment of how to make this tool, & a photo of it, is in http://bmwmotorcycletech.info/tools.htm , as item #8A. Note that making the tool requires a very small amount of welding. If you do not have a welder, or do not wish to have the tool made that way, you can just use a piece of allen wrench. The tools article also has photos of the clutch disassembly & assembly tools …you may need three if you have an early model; although three common bolts work well.

At this point I strongly suggest you go look at: http://bmwmotorcycletech.info/flywheelremovalwarning.htm

Whatever tool you use, be sure it cannot rotate such as to loosen its pressure on the inside of the outer cover if you rotate the flywheel in either direction. The advantage of my tool is that it is unlikely to allow the alternator bolt to loosen if the tool is made and installed correctly, as you rotate the flywheel. Be sure the tool is not ‘captured’ by raised grooves on the inside of the cover, etc. Think!

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The Dell’Orto Carburetor

If you can stomach all this reading and absorb and understand it all …you could become a DellOrto expert!

Be sure to see the information on the floats, it does pertain to Airheads, this is in section 3.2.2. See also near the very end of the long article below that you are reading, where there is my information on the pump setting and float setting, as pertains to BMW Airheads specifically! There are hints there too!

The following information article came from, I was told, the .startwin.com site, and was sent to me in a zip file, which I have unzipped, modified, and put below. I have been unable to find the author or person who might, or might not, have copyrighted this information, so as to gain official permission to place it here. This article, whatever its original source, now appears to be public property. I tried to make sure about that, so, on 10-06-2003, I sent e-mails to van Star Twin Motors, the Startwin.com folks, asking about use and copyright. There has never been a reply. I last viewed their website in November 2017, and there is nothing about the carburetors.

I have added my own comments to the article prefixed by ***, and underlined. I have corrected many typographical errors and misspellings in the original article …and changed to U.S. type English spelling and usage. I have also eliminated some in-article hyperlinking, etc. There are places that my comments now are not all that clearly identified, as I wished to eliminate red color I used in earlier versions of this article, which resulted in gaudiness and an unprofessional look to the article; so this latest version generally uses asterisks and underlines for personal comments by me as well as for normal emphasis. I have also modified how the original’s photos are formatted and placed, and added borders, and I also prevented wrapping of text around the photos.

The following informational article can be quite useful for those trying to understand how any carburetor works. While the information does not deal directly with Constant Velocity carburetors, it does deal with needle & slide carburetors, & a vast percentage of the information applies to all types.

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Alcohol-Proof Float Kit

The MAIN advantage of these kits is that you will likely never have to replace floats. That does NOT apply to the float needles, of which there were two basic types. The VITON tipped ones have the same easy-to-lose fine wire clip as on the stock carburetors. That clip insures positive float needle operation when the needle should be leaving the needle seat and allowing fuel to flow into the bowl.

If the original floats (which DO AGE) are already really bad, and/or the float needle is already bad, things will certainly improve with PROPER installation of these PRICEY kits! Installation is, however, somewhat tricky. IN MY OPINION, installation of these kits when the old parts were worn, often considerably, is the HONEST & TRUE reason that SOME find improvements with fuel mileage after installing the kits.

Adjustment of these dual-independent float kits is more involved than with the stock floats. These kits can cause $$$$ problems, so, please read all of this article.

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Synchronizing Carburetors

The following information specifically applies to carbureted twin cylinder two-valve BMWs, of the type known as “Airheads”, as manufactured 12/1969->1995+. Some of the information may be applicable to many other motorcycles, and even injected models, and to even single cylinder and two stroke engines. The method is applicable to BMW models before the above dates, and while the shorting method works for ALL, you CAN use the vacuum methods for those earlier models with, or install, vacuum ports.The author has used these methods on a wide variety of engines. The author is NOT responsible for any electrical shocks, nor other consequences, for any ineptness on your part in failing to understand and perform procedures properly and safely.

Quite a few decades ago many mechanics used a device called a Uni-Syn to balance carburetors. It was usable on almost any carburetor, and it was usable on most injected models (rare, then). Sometimes a minor modification was needed to allow the Uni-Syn to properly mate with the input area. The Uni-Syn was a specially machined or cast metal plate, rubber on one side to allow some pressure-sealing against the air intake side of the carburetor or injector, and an ADJUSTABLE venturi built into the plate, and attached to the venturi was a glass or plastic tube that had a floating ball in it. Properly used, this device would take accurate relative readings of the airflow through a carburetor or injection intake; then the device was transferred to the other carburetor (usable on engines with many carburetors too). I do not know if they are still available, I have one, and treasure it, as an antique! Treasuring some old tool does NOT mean I use it nowadays!

I do not! I have not seen one used, except in my own shop for some sports cars or 4 or 6 cylinder motorcycles, since the mid-1970’s, except to demonstrate its use. Mechanics had a lot of pride on their ability, without instruments, to listen to the engine; adjusting the idle mixture screw for a smooth idle, then setting idle rpm, and going back and forth until they ended up with the proper idle rpm and idle mixture adjustment. Some very experienced mechanics would even take bets on being able to synchronize a BMW Airhead engine without any special tools….and often made up stories about what they were doing….which, in truth was simply listening to the transmission internals rattling around at idle rpm (which they do, when the oil is hot). The throttle cables were synchronized by eyeball on lifting at the same time, and sometimes by transmission rattle. These methods are not good with multiple cylinder engines such as a V-6 or V-8 or inline 4, particularly those engines with more than two carburetors. The method is tricky to do with a BMW airhead boxer engine, and I do NOT recommend it. It is also NOT EVER as accurate as the vacuum nor shorting methods.

The primary method on the /2 bikes was to adjust the carburetor throttle stops for equal engine speed with first one plug cap, then the other, removed; you alternated between cylinders firing and not firing, back and forth. This was USUALLY safe on those magneto equipped /2 bikes because the magneto incorporated a safety gap, if the plug cap was pulled off the spark plug, the spark could jump across the safety gap. UNfortunately, sometimes the metal cap shell would give you an electric shock. This ‘lifting the cap’ method is still used today on the /2 bikes; although the shorting method is MUCH better.

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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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Carburetors

Some time ago a very embarrassed Airhead owner contacted me about how to ‘fix’ his carburetors. He has Bing CV carbs, and replaced the diaphragms, floats, etc. himself. Frankly, he is a bit ham-fisted. He also hates to ask for advice. He proceeded to nearly destroy his carburetors. The many e-mails with him prompted this article. There is a LOT of information in this article, and lots more on the author’s website. Carburetor work is not very difficult, easy to learn, and once you have worked on your carburetors, perhaps at such at an Airhead TechDay, you will wonder what all the fuss was about and you will find that it is easy the second time, and you might hardly need to refer to this article …or one of my others on carburetors…again.

I have my own ideas about when one should consider working on your Bing CV carburetors (and fuel tank and petcocks!):

YEARLY: depending on mileage and use: clean/dump float bowl contents, check corner bowl jet to be sure it is clear/open, possibly replace float bowl gasket if poor; empty gas tank, remove petcock(s), clean tank, dry it, clean petcock screen(s), possibly service petcocks internally if they are getting quite stiff to turn; or, if leaking. Inspect fuel hoses. I consider these things part of carburetor servicing. Failure to service the fuel tank will eventually be costly.

5,000 mile intervals: synchronize the carburetors, but ONLY AFTER the valve adjustment and ignition timing adjustments are checked FIRST.

30,000 mile intervals: replace float assembly (if original one piece assembly). Always also replace the float needle and clean out the central jet assembly. Replacing the float assembly is UNlikely if you have the alcohol-proof separate floats that Bing now offers. However, if you have those, be sure to replace the float needle and

{mprestriction ids=”4,5,6,8,9,10,11,12″} check the adjustment of the flimsy brass floats bridge, info on the Snowbum website in its own article on these independent float kits:
http://bmwmotorcycletech.info/bingindependent.htm

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Carburetor Rebuild Tips

“”My Bing rebuild kit arrived and I am having trouble removing the old slide needles from my 83 R100RT. Any advice on this and other Bing carb rebuild tips?””

There are two basic types of needle mountings. One type uses a captive hidden clip, and the other type has a screw that has to be loosened.

If you have to, use a pair of pliers and protect the needles with something like thin leather at the pliers jaws. BUT you might be able to remove the needles with clean and dry fingers or try soft thin leather gloves or kitchen plastic gloves. ROTATE the needle 90 degrees as you pull slightly downward, then repeat, until needle is removed. When replacing the needles, the same 90 degree rotation, with small upward pressure, is needed for each notch of needle adjustment/replacement. When done replacing the needles to what you think is the ‘correct notch’, be SURE the needles stick out of the bottom of the slides exactly the same amount…use a vernier caliper. I like to record that value. Mention of needle position is very commonly done by ‘notch’ number. The uppermost notch on the needle is

#1, and as the needle is adjusted to be higher and higher in the slide, the numbers increase, per notch, to #4.

Some needles, probably from about 1985, were made out of aluminum and the needle grooves (notches) tend to wear rather quickly. If the wear is high, that will allow the needle to be in the wrong position vertically; it can move up and down a LOT. All needles, aluminum or steel, will also wear on their sides, as does the associated needle jet. The needles are purposely free to move a bit angularly sideways, so normal vibration wears them, and their associated jet. Always replace needle and jet together when overhauling.

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