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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Pulse Air Injection, fuel & evaporative controls systems

Pulse air injection system; evaporative and fuel solenoids systems, as on BMW Airhead Motorcycles Pulse-Air (Clean Air) System Description: Beginning with the 1980 U.S.A. models, BMW incorporated a modification that injected clean air drawn from the aircleaner area into the exhaust ports. Only the rectangular air-cleaner motorcycles have this system. The purpose of this essentially […]

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Oil Discussion

This discussion is also likely applicable to most old flat tappet engines, including some VW, Porsche, old Corvettes, etc.

Revised by the Author 11/05/2007, 11/01/2009; minor revision on 06/02/2014; edit again on 06/20/2018

Over the years, oils have been a popular subject for discussions in our motorcycle publications, club magazines, & on-line LISTS & Forums and Facebook, etc. I am not sure just why that is, but I suspect it has to do with our society of easy fixitus, or ‘I need to do something to feel good’, maybe a panacea for the masses…and maybe male ego, ..and who knows what else!  Certainly there is a large amount of placebo effect. REAL facts are hard to come by, and so-called ‘evidence’ abounds, and may be quite difficult to verify. There is a considerable amount of so-called ‘information’. Some is good, some is anecdotal, some based on testimonials, some sort of like ‘my brother told me of his friend who has a friend who told him that…’; or, ‘my mechanic who has decades of experience, says….

Did you ASK that person just HOW he REALLY got that information he is giving you?   Does that mechanic friend have a sweetheart ‘deal’ with a particular oil’s distributor?  Has he ever REALLY seriously tested oils in Airheads?   How did he test them?   Has he looked at hundreds of Airhead cams and lifters?   Do YOU believe the stories often heard>>that “car oils are plenty good enough, you hardly need pricey specialty oils?”.    Some information even seems scientifically derived, and implies itself to be definitive; in MANY instances this is NOT SO. In addition, there is all that advertising. SORRY, but those hyped additives like Slick50, QMI, etc., and those tests on TV of engines run without oil….these are sideshows; you never hear the entire story of the tests.  DO NOT believe these folks. YES, it is true that you MAY (or may NOT) have SLIGHTLY less friction, SLIGHTLY higher fuel economy, etc. HOWEVER, you will also likely get much increased WEAR (YES, you can have LESS friction and considerably MORE wear!), the product may settle out or ‘clump’, thereby plugging oil passages and oil filters, and LOTS more ills. This can lead to oil starvation and catastrophic engine damage. As for additives like Bardahl or Rislone or Marvel Mystery Oil: don’t use them, they can remove the protective coatings on your engine parts.  
BUT:  There ARE A FEW places that Rislone can be of help, and one is temporary use in a Classic K-bike, to hopefully free up a slipping starter drive clutch….aka Sprag Clutch.

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Oil Coolers

Why an oil cooler?

Air cooled motorcycles can run quite hot in some situations. This includes large amounts of throttle power for long periods of time; pulling a trailer or sidecar where a lot of engine power is needed; extremely bad traffic conditions; use of fairings in general (particularly fairing lower center pieces that are not ventilated). Engine cooling is obviously worse in quite hot weather. Your BMW Airhead engine has more than enough cylinder fins & head fins to dissipate enough engine heat in most circumstances, including some fairly extensive stop & go traffic, & modest speeds pulling a trailer or sidecar. But, there are limits.

For proper engine operation, lubrication, protection, etc., engine oil should operate in a reasonable temperature range after the engine has warmed up; not too cold, not too hot. The oil also needs proper viscosity over its expected temperature range in the engine. Usually, a multi-grade oil such as 20W50 is used in our Airheads. Quality 20W50 motorcycle oil is far better than the old single grades type of oils, & is quite adequate for most conditions, but a thinner oil might be wise if temperatures are at or below freezing; perhaps a 10W40. 10W50 and 15W50 oils are also available.

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Oil and Filter Changes, Procedures, Technical Information, and the $2000 O-Ring

Your /5 and later BMW Airhead motorcycle has a well-deserved reputation for reliability and exceptionally long life.  Regular oil and filter changes based on both time and mileage are necessary.  Use of a quality oil and quality oil filter is highly recommended.  There have been quite a few different filter numbers, filter styles, and methods of fitting them and associated parts such as O-rings, gaskets, shims, and oil cooler attachments, over the years of Airhead production.  This article will attempt to cover all versions,  models,  situations.  HOWEVER, the Author’s website has several articles, number 49 through 51D, THAT SHOULD BE READ; these cover things in more depth; things you REALLY NEED to know.  Please be sure to read all those articles.

Failure to follow recommended procedures, particularly on /7 and later models, or any model with an oil cooler, can result in $$$ repairs. There is a critical white round large rubber O-ring used on the outer cover on models with oil coolers, and also used on later models without coolers. That O-ring must be in good condition, and under proper mechanical mounting pressure, in the proper way. A failure here can result in an engine rebuild costing at least $2000; and if the crankshaft failed, perhaps over $3500. Reading articles 49-51D on the author’s website AND the entire article you are reading will make you an INFORMED owner, highly unlikely to make an expensive mistake…or allow someone else to make such a mistake.    

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Torque Wrench Discussion & Conversions

BMW made some serious mistakes many years ago in converting metric to English values in various of their publications. They admitted this. In BMW Motorcycle Dealer Bulletin (Vol II, No 23,  dated 3/1982) BMW SAID NOT TO USE ANY PUBLISHED BMW CONVERSIONS FOUND IN BRACKETS IMMEDIATELY BEHIND THE MILLIMETER FIGURES, IN ALL SERVICE LITERATURE, INCLUDING RIDERS MANUALS, SHOP MANUALS, etc.   This means that BMW meant for you to NOT USE published foot-pounds of torque, or any other torque value other than the metric.   You can almost always TRUST BMW’s figures in Nm….although I recommend less torque, for such as spark plugs; wheel preload, ATU nut, alternator rotor bolt, and a few other places, with some special cautions on the flywheel (clutch carrier) bolts.

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Thinking about purchasing an Airhead? Beginning Wrenching/Maintenance

Are you thinking of purchasing a BMW Airhead motorcycle?? … have little or no or experience with them?  Want some straight talk?

Motorcycles, no matter the age, all have a certain and specific feel to them.

For very modern bikes, a description may include high competence, plastic marvels, electronic marvels, …but not always having any special ‘character’.  Special knowledge, & often special equipment, are often needed to analyze and repair them. It can cost $$$ at a dealership to do analysis & repairs. Those dealerships may be necessary for you when something ‘interesting’ happens; granted, the bike may …be more reliable over-all, depending on how you describe ‘reliability’. With a BMW Airhead, you can do most repairs yourself. Over-all, normal necessary scheduled simple maintenance is probably done more often with an Airhead. It is likely to be much easier to do …and there are vast amounts of history & knowledge easily available on the Internet, Mailing Lists & Forums, Club documents, etc. This is not so with the latest and greatest; nor, even motorcycles that are just a few years old.

Help is always available for Airheads from numerous informed sources. The Airheads were in production for a very long time (1970-1995); yet there are less than a handful of places, in all models, all years, that are well-known problem areas. Except for a few, all problems are fixable by YOU!  The Airheads will require modestly more regular maintenance of certain things, but most often these things take little time nor cost. More modern machines might require less often maintenance, but the maintenance then required can be involved and often expensive. These are all big generalities, yes, but there is a lot of truth here.

The Airheads will not give you some things the much more modern bikes will, such as very easy starting in any conditions (due to modern bikes having electronic fuel injection), super brakes (modifications will, however), fancy suspension and ride controls, and probably more horsepower than you should have. But, there is no other motorcycle, of any brand nor type, that has the over-all character of a BMW Airhead, and most riders fall in love with them. The reverence with which some have for these bikes is legendary, and good condition examples of any Airhead model are fetching higher and higher prices. 

The rest of this SECTION 1 was originally written by Greg Feeler on 07/07/2015, & posted to the Airheads LIST. The original Subject Title was “1971 R75 purchase questions”. I have Greg’s permission to add-to & edit freely, & I have done so. Because of the editing and additions, I have not put quotation marks in it.

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Technical Tips for Airheads

This is by no means a complete list of technical hints for your BMW Airhead motorcycle.   The Author’s website has well over a hundred technical articles.  The Author’s website is:
HTTP://BMWMOTORCYCLETECH.INFO/INDEX.HTML

 1. If you are trying to find out if your voltage regulator is faulty, or, bypass it in case of failure while on the road, and thus obtain charging; here is a simple method. I carry one of these ‘tools’ with me in my on-bike tool kit for testing purposes or on-the-road emergencies.

Obtain two each standard male spade connectors. Any autoparts store will have them.  These may be called ‘disconnects’ or ‘push-ons’. Crimp or solder them to a stranded insulated wire about 6 inches long. To use; simply disconnect the plug from the voltage regulator under the fuel tank. Insert the male spade ends of your test lead into the plug’s female openings for D+ and DF; those are the OPPOSED openings. Do NOT connect to the female that has a brown wire. You’ve now removed the regulator from the system and ‘told’ the alternator to go to as high an output as it can…which it will at something like 4000 rpm or so. WARNING, this is for brief testing only or for limping home at low RPM.  This is because riding any distance at high RPM will cook your battery and is also hard on the diode board, and every other electrical item. If your charging output is still low with the jumper connected, you have other problems.

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Model differences, Airheads and some pre-Airheads, revised by author Jan 10, 2021

For BMW vehicles, there can be confusion between the year of manufacture and the model year. This has sometimes caused problems with titles and registrations with various States. The actual “model year” motorcycle could have been produced near the end of the prior calendar year, due to the BMW company-wide vacation month in August and restart of production immediately after that vacation, in September. There are exceptions & anomalies …most of these are such as when a BMW bike was manufactured even earlier and mysteriously is identified by BMW as the following year’s model. This has happened with some Airheads and some Classic K bikes now and then. There is sometimes additional confusion, because, for 1984, BMW stopped stamping the last 7 characters of the 17 character VIN, always a 7 digit number, next to the oil dipstick of all engines.

For very considerably more information about VIN and Serial numbers, how to read all 17 characters of VIN’s, the sequencing, the anomalies, etc. see the following article: http://bmwmotorcycletech.info/IDnumbrs.htm

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