Category: Technical Tips

Replacing Rear Main Seal – 3 (Parkhouse)

This will be a long one… So I’ll break the reply into two parts: Tear down and reassembly.

Parts to have on hand… Rear main seal, oil pump O-ring, oil pump cover and 4 bolts (upgraded since /6 series), 5 new flywheel bolts, 4 driveshaft lockwashers, 4 driveshaft bolts, 6 clutch bolts, a new driveshaft boot if the old one is cracked or leaking.

Special tools… Clutch compressing screws (you can use bolts and nuts-less handy but works OK, or get from Ed Korn [see Links]), a flywheel brake (make out of bar stock or get from Ed Korn), rear main seal installer: from Ed Korn, 6mm allen drive on 3/8 socket, torque wrench, 10mm-12 point box end wrench (I like Snap-on’s), 27mm or 1 1/16″ socket (turned or ground down on outside), micrometer or calipers, slide hammer with hook attachment, impact screwdriver with large phillips bit.

Place bike on center stand (if a “Ride-off stand”, block up on 2X4s), you want to be able to turn rear wheel freely. Drain gearbox if work is planned on it. Drain driveshaft as oil will spill when it is disconnected. Remove gas tank, set aside out of way. Take carbs off cylinders and hang over front of cylinders, out of way.

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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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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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