1974 BMW R90S, 9,849 ORIGINAL MILES, ORIGINAL AND UNRESTORED

1974 BMW R90S– ALL ORIGINAL SURVIVOR, OWNERS FROM NEW, 848 ORIGINAL MILES, RAME AND ENGINE #4950456, anufactured 5/74

1974 BMW R90S– ALL ORIGINAL SURVIVOR, OWNERS FROM NEW, 848 ORIGINAL MILES, RAME AND ENGINE #4950456, anufactured 5/74

This BMW R90S epitomizes the late 1970’s sportbike/cruiser that became a permanent part of BMW’s reputation and still represents a high point in BMW history…

The condition of this machine is highly original and un-restored. It has just 9,848 original miles from new. The frame and engine numbers are factory correct and original. It is the 900 cc engine. The gearbox is also original to the machine. This R90 S is completely original and has never been apart. Everything from the paint to the seat to the frame to the wheels is original and the way it came from the factory. And everything WORKS. It is in un-restored and very nice original condition.

This machine has been in my collection for a long time, s started on a regular basis, nd ridden occasionally. I believe I am the third owner from new.

When I purchased the bike, t was in the same condition you see in the photos. I went through the machine top to bottom and checked all of the major engine, ransmission, nd braking components for functionality and safety.The gas tank is in very nice condition, he inside having no corrosion evident, he original Dell’Orto PHM38B carburetors were inspected, leaned, nd re-installed, he air filter checked, ll fluids changed, nd both front and rear brakes taken apart, leaned, e-built, nd re-installed, he consequence of the bike sitting idle for a long period of time when I acquired it.

The tires on the front rear are the correct and original type Continentals, hich are the only aspect of the bike which was replaced. They are in very nice and rideable condition. Both wheels, ncluding the original rims and spokes, nd are in excellent original condition.

The seat is original and the upholstery is in perfect condition with no rips, ears, r wear of any kind. Underneath the seat, ou will also see the complete R90S tool kit pictured. It is included with the machine.

The engine and transmission are in excellent interior condition due to the low mileage and absence of any type of harsh conditions or abuse throughout its life.

A complete cleaning and detailing was performed, nd although detailing on an original machine is never completed, he overall condition of the finishes is remarkable considering the age of the machine, nd is in line with the low original mileage.

The aluminum parts are in excellent condition overall, ut due to the originality, did not want to go too far polishing any parts.

The paint is Silver Smoke, nd as far as I can tell, s the original factory paint on the machine. It is the correct shade and application and is nearly flawless, xcept for a few miniscule imperfections on the front fairing. If you would like additional higher resolution photos of the paint, lease let me know and I would be happy to email them to you.

The original badges are still applied to the gas tank and tail section, nd the correct decals are on the side covers. All of the fairings, overs, tc. are in excellent condition and are not in need of any type of repair. The original touring luggage (pictured) is in beautiful original condition and obviously included in the sale.

The R90S on the road is very easy to handle, nd rides down the road very tight, ith no shakes, himmies, r rattles. It shifts and accelerates smoothly and holds the road as it should.

There is absolutely NOTHING that needs to be done to this machine to ride it occasionally and enjoy it as a showpiece. Unlike a lot of collector motorcycles for sale on the internet, his R90S is ready to ride and not in need of any expensive service once you get it home.

I have always tried to collect low mileage, riginal condition from the factory motorcycles over the years, nd I’ve been doing it for a long time. I’ve been selling some of my bikes over the past few years to make a little more space in the barn and hopefully add some new machines to my collection I haven’t had in the past. It all about having fun and never truly growing up.

I am always looking for new machines to add to my collection and love talking shop about old bikes in general. Please contact me if you’re looking for something or have something interesting you might want to part with. Or feel free to call if you have a great story and some photos to share about an old bike. That’s what our hobby is all about.

Thanks for your interest!

TERMS: $1,000 DEPOSIT WITHIN 48 HOURS OF AUCTION CLOSE VIA PAYPAL OR OTHER MEANS MENTIONED BELOW. BALANCE OF AUCTION AMOUNT MUST BE PAID BY CASH IN PERSON, ANK TO BANK TRANSFER, R CERTIFIED FUNDS (WITH VERIFICATION) ONLY WITHIN 7 DAYS OF AUCTION CLOSE. SORRY, O C.O.D. AND NO PAYPAL FOR FINAL PAYMENT…

The description of this motorcycle is written to the best of my knowledge. However, am by no means an expert on vintage BMW motorcycles. Please don’t hesitate to ask for more photos and, f possible, ome and look in person before the auction ends. ALL SALES ARE FINAL! If you have any questions, lease contact me before the auction ends.

If you have any questions, lease contact me. If you live close to Chicago, encourage you to come and inspect the motorcycle in person!

In an effort to protect the eBay user information and to help ensure the authenticity of correspondence between sellers and bidders, Bay’s new listing format does NOT display any bidder information. Nevertheless, STRONGLY encourage bidders to contact me directly to answer questions or to verify correspondence. Seller reserves the right to not accept bids or sell the vehicle to anyone with a zero or negative eBay feedback rating.

This motorcycle is being sold as is, here is with no warranty, xpressed, ritten or implied unless there is a warranty in effect from the factory. The seller shall not be responsible for the correct description, uthenticity, enuineness, r defects herein, nd makes no warranty in connection therewith. No allowance or set aside will be made on account of any incorrectness, mperfection, efect or damage. Any descriptions or representations are for identification purposes only and are not to be construed as a warranty of any type. It is the responsibility of the buyer to have thoroughly inspected the motorcycle and to have satisfied himself or herself as to the condition and value and to bid based upon that judgment solely. The seller shall and will make every reasonable effort to disclose any known defects associated with this motorcycle at the buyer's request PRIOR to the close of sale. Seller assumes no responsibility for any statements regardless of any oral statements about any part of the machine.

Please remember that your bid constitutes a legally binding contract to purchase this item. If you require an inspection, ave it done prior to bidding. I strongly encourage all bidders to inspect the motorcycle personally or enlist the services of a professional inspector prior to placing a bid. After the sale, nspections are not recognized as a contingency to completing your obligation to your winning bid. If there are any questions regarding the above terms, lease e-mail prior to bidding.

Please do not waste my time or yours bidding on an item you do not intend to pay for. If you bid on this part and win, ou are expected to pay for the part and pick it up in a timely manner!

I welcome ALL international bidders and am happy to assist with making shipping arrangements. I can also arrange crating for shipment on my end for a nominal extra charge. If you are an international buyer, understand it can take some time to arrange shipping, o I do not mind keeping the motorcycle for a longer period of time until pick up. Please contact me before the sale ends, f possible, o discuss the specifics.

For more on the BMW R90 S, lease read on past the photos….

The R90S was a sport bike produced by BMW and was first introduced in 1973. The R90S is considered by many to be one of the first superbikes, nd the first such machine from BMW. However, n retrospect it may have been one of the earliest incarnations of what would later be known as a "sport touring" motorcycle: a machine designed to cover long distances quickly and in relative comfort, articularly if the route between Point A and B was as twisty as possible.

Since its introduction, his motorcycle has become a kind of cult special and is of particular interest to vintage BMW motorcycle enthusiasts. There is even a dedicated National R90S Sport Owners Club, nd the American Motorcyclist Association included the R90S in its The Dawn of the Superbike exhibit.

The first U.S.A. AMA Superbike Championship was won in 1976 by Reg Pridmore riding a R90S. This type of engine is a 247 BMW and known as Airhead (motorcycle). It is especially well regarded amongst sportbikes from 1973-1976. Overall, t is the definitive ’airhead’ BMW as regarded by owners and fans alike.

Technical details:

The R90s BMW was an OHV, wo valve per cylinder, ir cooled flat twin, r boxer engined motorcycle weighing 215 kg and running a five speed gearbox through a shaft final drive. The model was an extension of the previous 750cc series /5 machines. The R90s was one of two 900cc models introduced in 1973 (1974 in Australia); the other being the 900cc version of the existing R75/6 machine, he R90/6.

There were three series of R90S:

Model year 1974 : 9/1973 to 8/1974 (6.058 units)

Model year 1975: 6/1974 to 9/1975 (6.413 units)

Model year 1976: 8/1975 to 6/1976 (4.984 units)

The first series of R90s sported a distinctive two tone paintwork (Black/Smoke) called "TT silberrauch" or "TT smoke silver" with adhesive gold pinstripes (no more hand painted by the factory; only the first series of R90S had this kind of pinstripes. The following complaints of the customer did convince BMW to turn back to hand painted pinstripes). Later variants (6/74 on) were sold both in "Smoke Silver TT" and "Daytona orange" (gold/silver smoke with red pinstriping). The R90s was an individual factory motorcycle - no two left the factory the same due to the individual differences across each motorcycle’s paint job. Look at two identical machines from the same production run and you can see this difference today - which makes restoration a subjective task.

The R90s sported a small but effective factory fitted Bikini Fairing, hich held four dial instruments (Speedo, ach, lock and Voltmeter). The first series R90S was only equipped with a 238 watt alternator (All other /6 machines had at least a 280 watt alternator), hich meant aftermarket lighting or heated handgrip accessories would be less effective on this bike. That’s why on the third series the alternator was upgraded to 250W.

The bike also possesses an adjustable hydraulic steering damper activated via a knob located on the steering head. Suspension is by telescopic forks at the front and twin shocks at the rear. The rear dampers were adjustable for preload, hich is the only suspension adjustment available. Aftermarket fork gaitors are often fitted to the bike but are not required due to the relative hardness of the fork stanchions.

Other critical engine differences are that the R90s came equipped with standard 38mm Dell Orto ‘pumper’ Carburetors, iffering from the previous 26mm Bing slide carbs or 32mm Bing CV carbs of the standard /6 and /7 800/1000cc series machines (later 1977-80 1000cc machines sported 40 mm Bing CV carbs). There are many, mall but important differences on the three series of R90S. On the first series, he brake discs are not drilled, nd the handlebar switches are the same of the /5 series. Restoring a R90S might be difficult because it’s very important to respect the correct features. For example, he wheel axle diameter of the first series is smaller than the one of second/third series...

Design:

The bike’s stunning visual design was overseen by Hans Muth, ho was brought into the BMW fold to create a machine with a unique presence far removed from the staid image offered by previous BMW offerings such as the fast, ell built, ut conservative R69S. This designer later went on to design the R65LS, nd also the Suzuki Katana.

The R90S also possessed a redesigned seat, ith a small, tyled ducktail, hich was regarded by some as a retrograde step for those that rode two up (given the relative comfort of the previous Denfield double seat on the standard /5/6 machines). However, his ducktail added a second underseat storage space to add to the original underseat tool tray - just perfect for lightweight waterproofs, xtra maps, r winter gloves.

Performance:

On the road, he R90s was a sweet running and capable solo/two up sports machine. The addition of either Krauser or BMW branded hard panniers and either a rear rack or over the cylinder ’toaster racks’ made the bike a capable tourer. Overall, he bike can exceed over 380Km on a tank of fuel.

Its performance today is modest when one compares it to 180+ HP K series BMWs; but the bike ran the quarter mile in around 13.5 seconds and went from 0-60 MPH (0-100 km/h) in just over 5.4 seconds - not bad for a 67 BHP pushrod twin. Impressively, t is capable of maintaining long distances at high speeds in relative comfort. With car-like maintenance intervals, t made good sense as a long distance sports-tourer for those that could afford one.

Tools and owner servicing were well thought out. The R90s came standard with a full toolkit, hand pump, first-aid kit and even a small hand towel (with an embroidered BMW logo on it). Owner maintenance is standard practice with these machines. Valve gear was adjusted by simple locknut, nd timing was taken care of by points (later replaced by electronic ignition in many models). Most other maintenance tasks were easily achieved due to easy access to most mechanicals.

Maximum torque is delivered at about 5,500 RPM and redline is at 7,200 RPM. Top speed is 190 km/h upright and 200 km/h on the tank. The bike will run at 190 km/h all day if required.

The bike will run close to redline all day/night, ut the relative fragility of the overhead valve gear is something that needs to be considered when running the bike over the redline, s it has no rev limiter as found on modern bikes. As the OHV engine pushrod valvegear components were designed ‘off center’ by four degrees to accommodate future plans to expand the R series bikes to 1,000CC, his slight offset produces additional tensions on the OHV gear at maximum revs that need to be considered by owners who ride over the limit.

As for brakes, wo 230 MM drilled discs were gripped by single ATE calipers, ith a 200 mm drum on the back wheel. The ’74 onwards model bikes make a distinctive noise under braking thanks to the drilled discs. Overall braking performance bettered the Japanese offerings of the time (especially in the wet), ut were substandard to contemporary Brembo systems (which were subsequently fitted to BMWs from the /7 series onwards).

The front brake’s cable activation system for all BMW /6 series bikes, ncluding the R90s, s also different to other brands, s the master cylinder is located on the top tube of the frame and is activated by a cable from the lever to the cylinder. The argument was that this system offered greater protection for the master cylinder in the event of a crash. Later /7 machines reverted to handlebar mounted Brembo master cylinders, ith disc brakes replacing rear drums until the advent of the R100R Mystic models in the 1990s.

Miscellaneous:

Another point of interest is that the bike was originally equipped with a manual engine crankcase breather, hich was superseded by a reed valve design on the /7 series. An original R90s (as with many /5/6 machines so fitted) makes a ’plopping’ noise at idle as the crankcase breather manually opens and closes: later reed type breathers retrofitted to earlier bikes see this interesting auditory quirk removed.

The electrical system was both adequate and reliable, ith a H4 Headlight providing adequate illumination for legal speed touring at night. The switchgear was upgraded in 1975 from the previous /5 system. The indicator switch now operated on the vertical plane, ather than the horizontal one used by most other manufacturers. Even in 2006, oth BMW and Harleys continue with some form of point of difference to the rest of the world’s manufacturers in this regard, or reasons known only to themselves...

The ignition key is placed on the left headlight mounting point. While accessible, t is ill advised to ride round with a huge bunch of keys hanging off the switch. Not only does paint wear occur, he effect of gravity eventually wears out the switch, ecessitating an expensive and avoidable rebuild.

The steering lock is mounted in the steering headstock.

Handling wise, he R90s was good so long as you are smooth in throttle application and sure of cornering line. Machines of this vintage are not ’point and squirt’ types of bikes. Lines need to be thought through well in advance and stuck to. Steady power on through corners helps immensely. Backing off in corners, r sudden throttle application, esulted in the cardan shaft effect of either the back of the bike squatting or lifting.

The tires too are minimal in comparison to modern bikes. The R90S’s 19 inch front/18 inch rear combination are undersized, ut adequate for most riding activities. One advantage of such a narrow tire combination is good stability on dirt roads. A downside is the effect that worn tires place on the frame - a head shake/tank slapper can develop on worn tires that mimic the feeling of loose/poor condition head bearings. Good tires are essential to good handling manners...

The worst part of owning an R90s is the gearbox. The five speed unit does work but requires such precise changes and gentle movements but firm application that it is impossible to make quick shifts either up or down the gearbox.

The R90s is still regarded as ’the one to keep’ and owners tend to hang onto them for longer periods. While the overall numbers of R90s produced were smaller than the more mainstream /6/7 BMW R series models, he model is still regarded favorably, nd for good reason.

From 1973 to 1976 17,455 R90s were sold. The R90s became the R100S in 1977, hich maintained the R90s bikini fairing, ut ran the full 1000CC engine, 0MM Bing CV carbs, nd altered paintwork. The mantle of the lead BMW factory twin was passed to the R100RS, hich by now sported a full fairing (note: ’specials’ such as the 4V Krauser and Fallert BMW’s are not compared in this article). Other factory variants such as the R100CS were also produced in later years. Many later R series ’mono’ bikes still visually resembled the R90s in order to retain a visual link to this significant model.

In closing, MW R90s machines were the original 1970s superbike, nd should be considered in the same league as other similar ’high performance’ bikes from earlier years such as the Brough Superior SS 100 and the Vincent D Series Black Shadows in terms of quality, xclusivity, echnological advances, verall performance levels, ost and impact on the riding community at the time of release. While Japanese and other European offerings such as the CB750 Honda, 1 900 Kawasaki and SS 750 Ducatis superseded the performance of the R90s in their own way, hese bikes could not compete with the overall package of performance, ongevity and sustainability of the BMW flagship. The title of the first superbike of the post 1970’s era rests with the BMWR90S.

There are many books about BMW boxers (including the R90S) but until now, nly one book dedicated to R90S: R90S by Ian Falloon, hich describes all the differences of the three 90S series.

SPECS:

1975 BMW R90S:

-Engine Configuration: Horizontally opposed air-cooled twin, ushrod operated valves, per cylinder

-Bore & Stroke: 90 x 70.6 mm

-Capacity: 898 cc

-Compression Ratio: 9.5 : 1

-Maximum Power: 67 DIN hp at 7000 rpm

-Maximum Torque: 55 ft/lb (7.6 mkg) at 5500 rpm

-Fuel: Dell’Orto PHM 38mm slide type carburettors; Micronic air filter

-Lubrication: Gear driven pump

-Ignition: Kettering

-Charging system: 12v 280w alternator

-Starter: Electric starter 0.5 hp

-Transmission: Gear driven primary drive, .00:1 bevel final drive (optional 2.91:1)

-Gearbox:

1st 4.40: 1

2nd 2.86:1

3rd 2.07:1

4th 1.67:1

5th 1.50:1

-Clutch: Cable operated single plate dry clutch

Chassis:

-Frame: Steel main and bolt-on subframe

Dimensions:

-Weight: 215 kg wet

-Wheelbase: 1465 mm

-Length: 2180 mm

-Seat Height: 820 mm

Front Suspension: Hydraulic telescopic

Rear suspension: Boge dual dampers, prings adjustable for pre-load

Wheels:

-1.85 x 19 front

-2.15 x 18 rear

-Spoked alloy rims

Tires:

-3.25 H 19 front

-4.00 H 18 rear

Brakes:

-Front: 260 mm stainless undrilled discs with floating single piston calipers

-Rear: 200 x 30 mm drum

-Fuel Capacity: 24 Litres (5 1/4 Imperial gallons) including 2.5l reserve

Performance:

Top Speed:

-Upright: 195 kph (121 mph)

-Prone: 200 kph+ (125 mph+)

Acceleration:

-Standing 400m: 13.3 sec

-Standing 1000m: 25.3 sec

-0-62.5 mph: 4.8 sec

-Fuel Economy: 55.7 mpg (Imp.) at 68 mph

*Article Courtesy of Anthony Kodack/Top Speed.com

More on the R90S including a road test…

BMW have always trod their own path when it comes to motorcycle design, o matter what the rest are doing, o amount of influence has ever found its way onto their drawing board. The R90S is one such example of how to do the same job in a very different way, SL takes a look to see why this Beemer was, nd still is, uch a winner.

In 1974, he R90S was head and shoulders above the rest of the opposition and was the machine that kept the Japanese honest, o much so that many original ideas found in the Boxer design were widely imitated. Yamaha for instance used an identical shaft drive set up in their new range of sports tourers, hile the handle bar fairing became both the norm for the next generation of sports machines and a much sought after accessory for those that came without one.

The R90S does just about everything in a different manner, ts chassis feels to be soft and compliant, n fact too much so for a sports bike, hile the engine never gets into a screaming rage, nd yet the package is superb in its own right, deceptively fast weapon for the accurate rider to excel on.

It is difficult to conjure up an exact opponent for the BMW. On paper so many machines show potential, rom the Honda Goldwing and Suzuki GT750 to the Moto Guzzi V7 and Kawasaki Z1. In reality none of those machines could match the total package that the BMW offered, ery high speed, ffortless mile munching and mechanical reliability. Add the 45mpg that the Beemer returns even up in treble figures and most machines pale into the distance with every petrol stop. The R90S was expensive however; nearly half the price again of the best of the Jap machines, aking it the choice of a select few who could afford the ride.

With a design of such longevity, ne would not expect much in the way of common faults and to a large degree this is correct. The R90 boxer engine is a tough old lump. The law of sod should dictate that the bike with the most comprehensively equipped tool kit is the least likely to need it and for once this is perfectly true. The R90S kit is over- subscribed with sockets and spanners aplenty, ll wrapped up in a snug tool roll complete with its own BMW badged towel to lay them out onto in the unlikely event of a road side malady. Even if something does go awry, he technology isn’t exactly hi-tech and most jobs can be tackled with the on board tools and a little no how, ry that with a Jap 4’s electronic trickery by the side of the road on a rainy night.

Unlike many bikes from the period the R90S is still capable of day-to-day use or even long distance mile munching, he Boxer engine remaining reliable and willing too while the laid back attitude displayed by the chassis is ideal for relaxed riding two up and fully laden.

Quite surprising is the compactness and narrowness when sat upon the Beemer, hat looks like a very big bike as you approach it becomes nothing more than a powerful middleweight once sat upon it. The bars are hardly wider than your shoulders and the footrests, ff set to match the cylinder spacing, ncredibly close together, round five inches further in than anything the Japanese have to offer.

Even the large capacity tank isn’t in any way bulky, chieving its five and a quarter gallon capacity with length and height rather than width. This instantly endears itself to the rider as you sit fully on the center line of the machine making the bike feel balanced and not at all the capacity it is. At low speed the bike is so easy to keep upright there is hardly a need for that comforting foot down, turns can be performed with consummate ease, eet up all the way, hile sitting at junctions and traffic lights can often be done the same way, he engine configuration helping no end in this aspect with very little weight above mid shin height.

Once on the move, ittle changes, he big German twin is agile, ithe and above all, ast. Ok, ou can’t go rushing around in a ham-fisted manner or the bike will get upset with you, nd the result will be one sour kraut. There is simply no point trying to run to the apex of a bend with the brakes on for instance. The front suspension is too soft and compliant to handle such abuse, hile the engine is a bit on the lazy side to cope with the late downshifts required for this technique. Far better to work in unison and make small suggestions to your new Bavarian buddy, actually the R90S was built at the new Munich factory) that way no one will get their nose put out of joint and you will be rewarded with a superlative ride. Get the braking, ownshifting and turning done well in advance then, ry to go through the apex on the gas, hat way the whole plot tightens up nicely and you will be exiting the corner at a far higher speed than an equivalent Jap machine.

Braking is positive and effective although some feel is lost as the front lever pulls a cable that in turn actuates the master cylinder deep under the petrol tank, his doesn’t afford the kind of feedback usually associated with hydraulic systems, ut it works none the less.

Gear shifts need to be positive, o half-hearted touches on the lever, real prod is required to get the Boxer engine to shift ratios. When you get the engine revs correct the gear will shift both effortlessly and without the clutch, et it wrong and it is as if you are trying to shift a breezeblock with your left big toe.

More difficult than going up the box is coming back down again, he engine speed must be accurately matched to the rear wheel speed to make this a smooth affair, ismatch either and the bike will let you know in a way that only trying to shift large engine components before they are ready creates.

BMW R90S Model history:

The R90S concept, n one form or another, ould have been produced as early as 1969 and had been considered for production during that period, onda’s release of the CB750, long with doubts as to the publics’ readiness for a 900cc motorcycle, o doubt delaying BMW’s intentions.

The engine was based heavily upon the previous R75/5 engine, haring the same stroke, ut with a larger bore, o give a capacity of 898cc. First seen in October 1973, he new machine quickly established itself as a front-runner with the press and public alike, eing the first bike from BMW that could genuinely run with the leading sports machines from Italy and Japan.

Released alongside a less highly specified R90/6 model, he new sportster featured several lessons learnt on the racetracks of the world. Roller bearings replaced bronze bushes for the rocker arms and the big engine breathed through 38mm Dell’Orto carburettors whereas all other Beemer’s used Bing units.

The electrical system was up rated over the /5 model Boxers, sing a Bosch three phase system, lthough the R90s actually produced slightly less power into the regulator. This was largely attributable to a smaller diameter rotor, equired to give a greater clearance between it and the stator windings, rankshaft flex being a major problem at high engine revs with the sportier version.

For 1975 there were a few updates and modifications, new crank shaft and front main bearing was implemented enabling a larger alternator to be fitted and the kick-starter was removed, lthough fitting one still remained an option. Wet weather braking was improved by drilling the two discs, nd fitting a 17mm wheel spindle, n place of the 14mm one of the earlier model, educed front-end flex.

For the final year of production, he engine was radically altered in readiness for the 980cc R100 series, irst seen in 1977.

BMW R90S Timeline:

1974:

The first of the R90S models was released to a surprised world come to expect sports bikes from any other manufacturer but BMW. The Hans Muth design was a success though and those that rode the machine quickly became a fan.

1975:

A few minor updates were introduced for the second year of production. The crankshaft became stronger and had a new main bearing design to prevent flex along its length while new handle bar switches and controls were implemented to improve ergonomics.

1976:

There was a new, arger capacity machine waiting in the wings and the final year of production reflected this. The R90S from 1976 already had the improved casings to facilitate the bigger pistons along with improved cylinders heads and many more modifications in readiness for the R100RS seen the following year.

*Article Courtesy of ClassicMotorbikes.net

The BMW R90S is a sport motorcycle that was produced by BMW between 1973 and 1976. The first United States AMA Superbike Championship was won in 1976 by British rider Reg Pridmore on a R90S.

Technical overview:

This R90S is fitted with a type 247 engine, therwise known as an airhead. The engine is an OHV, wo valve per cylinder, ir-cooled flat-twin, r boxer engine. The R90S weighs 215 kg (470 lb) and has a five-speed gearbox with a shaft final drive. The R90S was introduced with the new BMW "/6" series along with another new model the R90/6. The R90S and R90/6 were introduced in 1973 along with the revision of the already existing 600 cc and 750 cc bikes that were now called R60/6 and R75/6. The earlier R50/5 of the "/5" series was dropped.

There were three series of R90S:

Model year 1974: September 1973 to August 1974 (6,058 units)

Model year 1975: June 1974 to September 1975 (6,413 units)

Model year 1976: August 1975 to June 1976 (4,984 units)

The first series of R90S sported a distinctive two tone paintwork (Black/Smoke) called "TT silberrauch" or "TT smoke silver" with adhesive gold pinstripes, hich later changed to hand painted pinstripes.

The R90S sported a small but effective factory-fitted Bikini Fairing, hich held two dial instruments (clock and voltmeter) in addition to the normal instrument binnacle's speedometer and tachometer. The first series R90S was only equipped with a 238 watt alternator, hile the other "/6" machines had at least a 280 watt alternator). The third series R90S alternator was upgraded to 250 watt.

The bike also possessed an adjustable hydraulic steering damper activated via a knob located on the steering head. Suspension is by telescopic forks at the front and twin shocks at the rear. The rear dampers were adjustable for preload, hich is the only suspension adjustment available. The R90S came equipped with standard 38 mm Dell'Orto 'pumper' carburetors, iffering from the previous 26 mm Bing slide carbs or 32 mm Bing CV carbs of the standard "/6" and "/7" 800 cc, 00 cc and 1000 cc series machines. Later 1977 to 1980 1000 cc machines sported 40 mm Bing CV carbs. The R90S differed from the R90/6 by sporting a 9.5:1 compression (R90/6 was 9:1) and 38 mm DellOrto round slide carbs instead of the 32 mm Bing CV carb on the R90/6.

There are numerous differences on the three R90S series. On the first series the brake discs were not drilled and the handlebar switches are the old "/5" series style. The first series was also still equipped with a "/5" series kick start lever and the front axle diameter is smaller than that of the second and third series.

Appearance:

The bike's visual design was overseen by Hans Muth, ho was asked by BMW to create a machine with a unique presence far removed from the staid image offered by previous BMW offerings such as the R69S. This designer later went on to design the R65LS, nd also the Suzuki Katana. The R90S possessed a redesigned seat, ith a small, tyled ducktail, hich added a second underseat storage space to add to the original underseat tool tray suitable for lightweight waterproofs, aps, r gloves.

Performance:

Its performance is modest compared with modern BMW bikes that produce more than 180 bhp (134 kW). Maximum torque is delivered at 5,500 rpm and the engine redline is 7,200 rpm. The 67 bhp (50 kW) pushrod-twin engined bike could reach a top speed of 124 mph (200 km/h), an the quarter mile in around 13.5 seconds and went from 0–62 mph (0–100 km/h) in 4.8 seconds.

Two 230 mm drilled discs were gripped by pivot-pin ATE calipers, ith a 200 mm drum on the rear wheel. The front brake's cable activation system for all BMW "/6" series bikes, ncluding the R90s, s also unique. The master cylinder is located on the top tube of the frame below the tank with a standard brake fluid reservoir and is activated by a cable from the handle bar brake lever. The argument was that this system offered greater protection for the master cylinder in the event of a crash. Later "/7" machines reverted to handlebar mounted Brembo master cylinders, ith a single disc brake replacing the rear drum.

The R90S came standard with a full toolkit, hand pump, first-aid kit and even a small hand towel with an embroidered BMW logo.

Other features:

The bike was originally equipped with a phenolic disc and spring engine crankcase breather, hich was superseded by a reed valve design on the "/7" series. An original R90S (as with many "/5" and "/6" machines so fitted) makes a 'plopping' noise at idle as the crankcase breather manually opens and closes: later reed type breathers retrofitted to earlier bikes removed this feature.

A H4 headlight provided illumination. The switchgear was upgraded in 1975 from the previous "/5" system. The indicator switch now operated on the vertical plane, ather than the horizontal one used by most other manufacturers. As of 2009, oth BMW and Harleys continue with different switchgear to manufacturers in this regard. The ignition key is placed on the left headlight mounting point. The steering lock is mounted in the steering headstock.

Production numbers:

From 1973 to 1976, 7,455 R90S models were sold. The R90S became the R100S in 1977, hich maintained the R90S bikini fairing, ut ran the full 1,000 cc engine, 0 mm Bing CV carbs, nd altered paintwork. The mantle of the lead BMW factory twin was passed to the R100RS, hich by now sported a full fairing (note: 'specials' such as the 4V Krauser and Fallert BMW's are not compared in this article). Other factory variants such as the R100CS were also produced in later years, porting spoked wheels and black-painted square valve covers; as a sort of 'licht' derivative that was available only in black bodywork.

Legacy:

A later example of the R259 oilhead BMW, he R850/1100R, ported a similar two-tone smoke grey paint scheme in homage to the original BMW 'superbike' color scheme.

Two R90S bikes placed first and second at the very first AMA Superbike race at Daytona in 1976. On the first place bike was Steve McLauglin and on the second was Reggie Pridmore. The first place bike is now in the BMW Mobil Tradition Collection.

Further reading:

Falloon, an (2006). BMW R90S. Whitehorse Press. ISBN 1-884313-56-6

References:

- "BMW R90S Specifications". BMbikes. Retrieved 12 August 2009.

- "Media Guide 2007" (PDF). AMA Superbike Championship. p. 302. Retrieved 2007-09-20.

- Roland Brown (Premier Issue). "BMW R90S: Bahn Storm". Motorcycle Classics. Retrieved 2009-08-24.

- "R90S Specifications". bmbikes. Archived from the original on 13 December 2010. Retrieved 21 November 2010.

- Motorcycle Classics, an/Feb. 2010 p.18

Thanks for your interest. If you have any questions, lease feel free to contact me.