/5 /6 and /7 Airhead Design Blunders

[Ken in Oklahoma]

I reckon that title got your attention!

I don’t really know what might have prompted this post. But these thoughts have been brewing for quite a while now. For the record I regard airheads as fine motorcycles, certainly better than their contemporaries. But even fine motorcycles, perhaps like fine women (and men) have their flaws. See what you think about my impressions.

Caveat: some of my comments may only serve to reveal my ignorance, or simply lack of experience. Plus I was using Haynes and Clymer manuals which weren’t very good. So some of my criticisms may be totally unfounded. Responses to this post may be another learning process for me. But I reckon I will mirror frustrations y’all may have had dealing with the machines we like.


Rear Wheel Bearing Stack
The first time I had to replace a bearing in the rear wheel I paled when I saw what had to be done to change out and preload the bearing(s). Heating up the hub and pulling the stack was daunting. Plus, I imagined a lot of wear and tear on the hub. But then using a threaded rod and fabricated disks to hold the stack together so you can select the correct “wedding band” spacer by feeling how tight the outer drum was seemed at best not very reliable. I had little confidence that I had gotten it right after making my decision. But I did my best and hoped for the best. And I never had a failure.

I have to wonder, though, how many BMW mechanics were really adept replacing the rear wheel bearings.

(Note, since my first experiences I have learned a lot more about the bearing system. And the stack has to be pulled only if the drive side bearing is faulty or a suspect. And that bearing is in a better environment than the “car-wash” environment of the other side. Duane Ausherman’s writings were a bit of an epiphany for me. I learned that you can do a fine job of evaluating the preload of the bearings without pulling the stack along with other things.)

I guess the thing that bugs me the most about the “stack” is that with the advent of the snowflake rear wheel BMW decided that a stack wasn’t needed after all. And, of course, a stack never was needed for the front wheels.



Rear Wheel Splines

The splines mating the rear wheel with the final drive have vexed me ever since I changed my first rear tire. The main concern here is that the splines, both on the final drive and the rear wheel hub do wear. And renewing the splines on the final drive is an expensive proposition. The splines in the hub can be replaced with attention to what you’re doing. But why were there splines at all? Why would lug bolts not have worked well? They seem to work well enough on the monolevers.

I’m guessing the reason why splines were used in the first place was for competition. If you need to replace a wheel fast, that is in competition, splines are the thing to have. BMW was involved in racing and ISDT competitions.


7 Inch Headlight

I’m probably being picky on this one. I seem to remember in some of their airhead flyers BMW bragging about their 7 inch headlight. But is it better? The size of the reflector doesn’t seem all that important to me. It’s the bulb wattage, the quality of the reflective surface, and the quality of the lens that would seem most important. Plus a sealed beam 6" headlight would only require replacing, as opposed to replacing a dulled reflector. It would be so simple to just pop in a new unit.


Side Stands

I’m not harboring any grudge on the /5, /6, and /7 side stands. They work well for me. But I’m tall and long legged, so I can even deploy the side stand from the saddle (except for the last inch of travel.) But I think a rider with a shorter inseam has a problem. He must hold the bike up as he dismounts and then deploy the sidestand And if he’s riding a heavily packed bike, such as when Dwerbil came to the first rally on his /7, he has to hold the laden bike up as he struggles to get his right leg on the left side of the bike past the load. And then he can deploy the side stand.

(Getting along with the side stand on my ‘91RT Monolever was another story. I couldn’t get my toe on the damned tab from the saddle. It’s now wearing a Brown sidestand.)

Side stands do have a reputation for excessive wearing, but that hasn’t been an issue for me.

Perhaps the /5, /6, and /7 sidestand “issues” are why their center stands are so often worn through. That and riders carelessly “throwing” their bike onto the center stand, skidding it across the concrete.


Under The Tank Master Cylinder

I’ve never understood the under the tank front brake master cylinder. One of the main advantages of a hydraulic braking system is somewhat nullified by operating it with a cable. I’ve read speculation that BMW was concerned about passers by screwing around with the master cylinder. That’s as good of a reason as I can think of. But the long term issues with the under tank master cylinder can be dire. Out of sight is out of mind and most /6 and /7 bikes I’ve seen have had the master cylinder leak at one time (or more). That’s bad enough but the leaking brake fluid has a tendency to wick into the starter relay connector on the L/H side of the upper frame tube. On my /7 the engine and all electrics died. Luckily it was at my front gate rather than miles from home on some lonely Oklahoma byway. The problem was a corroded/mucky connection between the starter relay and it’s mating receptacle. As has been noted, the 12V positive red wire from the starter solenoid goes to one terminal of the starter relay connector, then thru the relay itself, and then from another terminal on the same connector to the headlight shell. (I’ve heard that BMW did it that way in order to build a less complicated wiring harness and the relay connector (with appropriate relay) was a good way to connect two sub harnesses together.)


5 Speed Transmission Shims, Dogs, and Kickers

I’ve not been inside a 5 speed transmission yet, so most of what I’m going to talk about came to me through osmosis. (Hi Duane) To be sure, overhauling or fixing a 5 speed transmission is a daunting proposition. Plus the 5 speed transmission isn’t very reliable in the first place. The kick start (on the few 5 speeds so equipped) simply isn’t reliable. And the transmission dogs are prone to breakage because they were not machined well. (I was heavy throttle torquing on an entrance ramp of a highway when suddenly my engine quit pulling and revved up. Yup, lost a gear because of broken dogs.) BMW, or rather BMW’s supplier should have done better. And BMW should have changed the specs given to the supplier.

The chief concern about going into the transmission is to get the shim stack right. There are tedious calculations to be made and you never know for sure if you’ve got the shim stacks right. I wonder how many transmissions have failed for that reason. And I doubt that one in a hundred of BMW dealers ever owned up to mis shimming the transmission.

So how should BMW have done it? That’s a good question. I’m thinking that on the back side of the transmission BMW should have had had caps on the back side of the three shafts. The covers could be removed and the bearings re-shimmed as needed. Or (this is even wilder) perhaps an inspection hole to the shim stacks could have been created where removing a screw would reveal the shim stack for evaluation. Neither of my ideas are very good, but the situation as it is, is a bitch.


Valve Recession.

The world wide conversion to unleaded fuel caused a lot of problems for a lot of manufacturers, BMW included. So I can’t really fault BMW for the valve seat recession problems that showed up. But what bugs me is that the fix fixed the valve seat recession and instead now the valve heads were tuliping. That bugs me.

Ba dip, ba dip, ba dip, that's all folks!


Ken, overly critical in OKlahoma

[bbelk]

I reckon that title got your attention!

Ken, overly critical in OKlahoma

My initial response was going to be "BLASPHEMY" but then I thought about it.

Rear Wheel Bearing Stack: I watched it done once at one of your rallies, but I am too chicken to do it myself. I had them replaced by a shop when I bought my new bike (the 79 R65). On my old bike (the 75 R90) I just stick my finger in there and see if things feel smooth to rotate. I am too chicken to go into it. Maybe it will get done at tech day in May. Is Larry Fixit coming?

Rear Wheel Splines: No failures here and it is very impressive the amount of slack that seems to be tolerated by the bike. My R65 with 34,000 miles has much less play than the R90 that is approaching transmission number 3, putting its mileage somewhere around 150,000, but I will never know for sure because of one more thing that I would add to your list which is the speedometer/tachometer inaccuracy and fragility. I have been told by Mikey from Martindale Motorcycle works (who also bought out Airhead salvage) that I should take good care of the Tach because the used market has dried up and there is no new market availability.

7 Inch Headlight: I think my R90 has a 6 inch and those lenses are all over the place. My R65 has the 7 inch so it was of course the one that took the rock and had to get a very expensive replacement.

Side Stands: Both bike have Brownstands and there is a special place in Hell reserved for the designer of the original. The center stand on my R65 has failed such that it swings too far forward to the point that both wheels sit on the ground. It is useless for tire changing and is quite hard to destand. I think fixing it will take some trick welding that I am not yet capable of and the motor might have to be removed to do it.

Under The Tank Master Cylinder: This designer will be in the room next to the kick stand guy. I put a handle bar mounted cylinder on the R90 bringing it up to merely below average braking rather than holy shit my feet are getting hot from dragging them on the ground to stop.

5 Speed Transmission Shims, Dogs, and Kickers: How can a box this big, with gears this heavy, fail so quickly after spending its life shifting no better than a tractor at its very best. I must admit though that achieving a smooth clean shift is one of the great joys that I get out of riding my airheads. Nobody with a Honda understands this. The gear box also has the value of providing approximate mileage on an old bike after the odometer fails. If it works, and has not been replaced, the bike has less than 75K on it.

Valve Recession: Done on the R90 but not yet on the R65. I didn't know the valves still had a propensity to fail after the fix so that is a new angst for me.

You post may lead to a healthy discussion and coming from someone with your unquestioning love of the machine, perhaps it is not blasphemy after all.

[Major Softie]

I guess the thing that bugs me the most about the “stack” is that with the advent of the snowflake rear wheel BMW decided that a stack wasn’t needed after all. And, of course, a stack never was needed for the front wheels.

Ah, never say never. As I recall, the /2 has stacks in both wheels.

[Ken in Oklahoma]

Ah, never say never. As I recall, the /2 has stacks in both wheels.

Good point. I'll never say never again.

Stacks in both wheels because the wheels were interchangeable front to rear?



Ken

[Ken in Oklahoma]

Rear Wheel Bearing Stack: I watched it done once at one of your rallies, but I am too chicken to do it myself. I had them replaced by a shop when I bought my new bike (the 79 R65). On my old bike (the 75 R90) I just stick my finger in there and see if things feel smooth to rotate. I am too chicken to go into it. Maybe it will get done at tech day in May. Is Larry Fixit coming?

Brad, I've sent a couple emails to Mr. Fixit, but no response. Perhaps he's traveling somewhere with Usi. I'll be trying to contact him again. It's hard to imagine a rally without Larry fixing everything that stands still long enough.

Ken

[Motorhead]

AS MY ONERSHIP HAD MOST OF THE GRIPESS PRINTED

I do like your idea about drilling the tranny for plugs to measure shim

no bike I ever owned was perfect

but this mule tested /5 has delivered 600+ mile rides a day even a Iron butt 1000

as my Lou Gearigh is gaining... this bike has been the best, do the work

my fix for the /5 make 1 key and replace the bucket for a 7" that removes some of the cost with bettrer light

braze a 1/8 steel bar to the form to make stronger and repairability

the bike is under restored to orginal form although 900cc and 5 speed... I'll call it toaster unchromed

[Major Softie]

Ah, never say never. As I recall, the /2 has stacks in both wheels.

Good point. I'll never say never again.

Stacks in both wheels because the wheels were interchangeable front to rear?


Ken

Correct

[ME 109]

Good idea for a thread ken, us curmudgeons need to blurt it out every so often.

Tapered bearings, full stop.

Oil filter accessibility on faired bikes. BMW painted themselves into a corner here.

/7 seat hinges. Attachment to seat pan, and attachment to lugs on frame. Weak as piss.

Requirement to block the crank.

Grounding point on tranny.

Other than that, STEP BACK FROM MY RS, STEP BACK I SAY!

[Deleted User 62]

Well, there's always the /5 SWB switch to LWB to fix a problem with the forks, the failure prone '74 5 speed transmission and wasn't there a problem with wheel spokes on the early /5 ?

[Major Softie]

ME's best hit is the oil filter issue. That was a very stupid design.

Speaking of oil filters......

I think the changing designs of the oil filter housing that led to the $2000 O-ring would have to be right up there too.