10 Days with a 1975 BMW R90 /6

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The R90’s front disc brake is a bit wooden, though an improvement over earlier BMW drum brakes. Modern Metzler tires also aid in the grip and handling department.
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3 / 10
Opposed-twin engine layout makes for easy maintenance and a low center of gravity.
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Valve adjustments are easy with the cylinder heads sticking out in the air.
7 / 10
Changing the air filter requires removing the left carburetor, but don’t let that scare you.
8 / 10
Len Kerkhoff knows BMWs inside and out, and enjoys restoring these great vintage road bikes.
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10 / 10

1975 BMW R90 /6
Years produced:
Claimed power: 60hp @ 6,500rpm
Top speed: 115mph (period test)
Engine type: 898cc, air-cooled, two valves per cylinder, horizontally-opposed twin
Weight: (wet) 210 kg (462lb)
Price then: $2,950
Price now: $2,000-$4,500
MPG: 45-50

As the largest of BMW’s new line of Slash-Six models introduced for the 1974 model year, the BMW R90 /6 plugged an important hole in the famed Bavarian company’s line-up. In the growing American marketplace, bigger was increasingly better, and prior to the 898cc R90/6, the largest bike in BMW’s stable was the 745cc BMW R75 /5 introduced in 1971.

While the R75 /5 was a competent road bike, it was decidedly old-school compared to the new flash coming out of Japan, and, perhaps more importantly, a bit slow. 

To get the new R90 up to speed, BMW bored out the R75’s 745cc engine to 898cc, giving the new bike 10 more ponies (60hp versus the R75’s 50hp). Top speed went from a previous best of 108mph for the R75 to 115mph for the R90, and unlike the R75, it was easy to hustle the R90 past the magical 100mph mark. For the R90/6 BMW swapped the R75’s front drum brake for a 10.25in disc, dropped the combined speedo/tach for more standard and sporty looking individual units, upgraded the handlebar switchgear and adopted a new five-speed transmission in place of the R75’s four-speed unit. It was also the first BMW without a kick starter.

When the R90 /6 was introduced, it was an instant hit with the motorcycling press. Cycle World magazine was agog over the new model, telling its readers in its February 1974 issue, “The new BMW R90/6 is so exciting it’s difficult to find a point at which to begin describing it,” while Cycle Guide called it a “powerful motorcycle, designed to compete in the performance-conscious market of 1974.” The R90/6 was even accepted into the growing camp of sportbikes, with Cycle World claiming the bike showed that “BMW is serious in its intention of producing the lightest, best handling Sportbike around.” We’re not sure we’d call a 462lb bike light, but compared to the 542lb 903cc Kawasaki Z1, the R90/6 was clearly on the svelte side.

Production of the R90 /6 phased out in 1976, by which time BMW had sold over 21,000 copies, making it the most popular model in BMW’s /6 line-up. After 1976 the R90 designation disappeared, replaced by the 980cc R100 line.

Riding the R90 /6 today
The R90 /6 we sampled is a 1975 model loaned to us by classic bike and BMW enthusiast George Paley. It’s not everyone who will let you take their pride and joy for a quick ride, let alone hand it over to you for 10 days. But George was genuinely intrigued to see what we thought of his Beemer, and bravely (some would say foolishly!) handed over the keys for our test.

Read about George Paley’s experience owning and riding the 1975 BMW R90/6

An excellent, original-condition survivor, George’s bike had just over 42,000 miles on it when we picked it up, and is a perfect example of how well Beemers hold up in the hands of sympathetic owners. The original black paint still shines and the chrome hasn’t lost any of its luster, and except for a flat tire that kept us from a final Sunday morning ride it performed almost flawlessly.

Getting familiar with the R90 is easy. The switchgear is mostly logical, although it took us a bit to get used to the blinker switch on the right-hand instrument cluster, which pushes down for left and up for right. The instrumentation is clear and simple, with the speedo to the left and tach to the right. Starting the R90 is a simple matter of turning on the fuel, giving it a bit of choke and thumbing the ignition button. Starting on our bike was mostly immediate, although it was a bit rough on warm mornings, when it seemed hard to dial in just the right amount of choke for a smooth start.

Warm-up was generally quick, and the bike would settle into a steady idle after less than a minute. The cable-actuated clutch is a bit stiff, but that’s not too surprising given the bike’s automotive-style, single-disc dry clutch. Clutch feed is smooth and linear, making it easy to pull away from rest regardless of terrain. Shifting into gear produces an audible “clunk” that’s familiar to anyone who’s ridden an old Beemer, although it is quieter than earlier models. Cycle World‘s review claimed that BMW had finally exorcised that familiar clunk with the R90, but our experience suggested otherwise, with the exception of the shift to fifth, which generally produced a nice quiet “snick.”

The R90’s heft makes low-speed maneuvering a bit awkward, but get it out on the road and it turns into another machine. Thanks to bags of torque (53ft/lb at 5,500rpm —  by comparison, a Z1 only developed 45ft/lb, and at a heady 7,300rpm) the R90 pulls like the proverbial train from idle to 6,500rpm. An indicated 80mph comes up faster than you’d expect, and the R90 feels like it would happily hold that speed all day long.

High-speed stability is excellent, and while we wouldn’t really characterize the R90 as a sportbike as Cycle World did, its handling in the twisties is surprising. By contemporary standards the R90 is nothing if not staid, but start hustling it through some corners and you’ll be surprised by its predictable handling, aided, we’re sure, by the bike’s low center of gravity, a nice side benefit of its low-slung opposed twin. Likely another part of the bike’s predictable handling are the modern ME33 Metzler tires the bike is running.

Cycle Guide praised the R90’s front disc brake, but we found the unit on our bike to be wooden at best, requiring a great deal of effort to haul the bike down from speed. We don’t know if the calipers on our test bike needed an overhaul or if the brake pads were the wrong compound, but it didn’t feel right. And while the rear drum on our bike had good grip, we thought it was overly sensitive and easy to lock.

Summing it up
We walked away impressed from our time with the R90. During the 10 days we had it we racked up just under 350 miles in a variety of conditions, and on a variety of roads ranging from smooth, six-lane Interstate highways to crumbling back road blacktop lanes. We found its upright riding position comfortable with an easy reach to the bars, although we think our bike’s firm seat would benefit from some added padding.

The switchgear felt surprisingly cheap, but it’s lasted this long and still works fine. Fuel efficiency was good, the bike returning an average of 46mpg, and it didn’t use a drop of oil. Since it’s a shaftie we didn’t have a drive chain to worry about, and the maintenance we did shows these old airheads are easy to work on.

Adjusting the valves, for instance, requires little more than lining up the timing mark and rotating through for each valve. It takes just a few mintues to remove each valve cover, and with the cylinders hanging out in the breeze the valves are, well, a breeze to adjust. At first glance the air filter appears buried inside the engine’s tall mid-section, and first-timers are often a little queasy about having to remove the left carburetor to gain access to the air filter. They shouldn’t be, because it all comes apart and goes back together easily.

We think the BMW R90 /6 is a perfect machine for the classic bike enthusiast looking for a comfortable and reliable touring machine. Its winning combination of classic looks, legendary reliability and fine road manners make it easy to live with, and its flexible, surprisingly powerful engine makes spirited riding easy, if not down right fun. Add to that an established network of supportive and knowledgeable parts and restoration experts — and riders — and you have a classic bike ideally suited for everyday use. MC

Restorer’s view
Len Kerkhoff
Autobahn Craftwerks,
BMW restoration and service
Cincinnati, Ohio
(513) 591-2629
autobahn@fuse.net, www.autobahn-craftwerks.com

Len’s story: “I’ve been riding since I was 6 or 7 years old. I started out on little scooters, and then when I was 15 my brother gave me a Bonneville. I didn’t start working on bikes professionally until about 15 years ago. Before that, I was into racing and working on race cars, mostly Porsches and German stuff.” Len’s daily ride? A 1977 Belgian R100RS police bike rated at 137mph from the factory.

Why BMWs: “It’s the only vintage bike I could find and restore, and send people out on the road without worrying about them breaking down. I’ve ridden a lot of bikes, and when I stumbled onto BMWs I latched on to them.”

Problems to look for: “Make sure all the switches are in good shape, because they break and cost about $140 a set. And keep an eye out for the rear drive splines, which can wear badly if not kept lubricated. Another common problem is with the diode board for the charging system, which is prone to failure. If the charging system is bad, the best thing going now is an alternator conversion from Euro Motoelectrics that gets rid of the diode board, gives 400 watts and is rock solid.”

Service recommendations: “I’m a real freak for valves and timing. If the timing gets out more than twice in 5,000 miles, it’s probably time for a new timing chain. I do the valves every 3,000-5,000 miles, and I lube the drive spline every time the rear wheel’s off. I also suggest electronic ignition. I’ve been using the Boyer, which I think is a great unit.”

Why you want a BMW: “Because they’re so damn rock solid and dependable, and you can get parts for them. That, and most of the people who have one will help you out.”

Additional technical infoTotal production: 21,097
Carburetion: Two 32mm Bing
Transmission: Five-speed
Front suspension: Telescopic forks
Rear suspension: Twin shock absorbers, adjustable preload
Front brake: 260mm (10.25in) disc
Rear brake: 200mm (8in) single-leading-shoe drum
Fuel capacity: 18ltr (4.75gal)
Oil consumption: None during test

Clubs and information 

BMW Motorcycles of America 
Airheads forum
• Internet BMW Riders

Parts and services 
Autobahn Craftwerks
Bob’s BMW
Blue Moon Cycle

Read more about the motorcycles mentioned in this article:
10 Days with a 1973 BMW R75 /5

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