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BMW R75/7 R100/S Road Test

1977 BMW R75/7 1977 BMW R100S

Motorcyclist Illustrated April 1977

Tucked away just off the Bath Road in Slough is a motorcycle shop. It hasn't got any big glass fronts or gaudy neon signs. In fact, if you didn't know it was there, you'd probably never notice it as you flash by to or from London on the A4.

It's just a little blue and white conver­ted cottage, resolutely defying any attemp to recognise the chromium-plated superbike age. It belongs to Chas Coombe, a BMW dealer for more years than he cares to remember: one of the originals.

Concessionaires, importers and hyper-salesmen have come and gone. But Chas is still there, literally minding his own business, and will be long after the others have returned to selling sports cars and washing machines.

Chas doesn't sell that many BMWs these days. He could. But he prefers not ot. He spends a lot of his time working on bikes for the Thames Valley Police. But he's also been carrying on a sort of one-man rearguard action against the trend new motor­cycles have taken. He's never quite forgiven BMW for dropping the R69.

I first met Chas about half-a-decade ago not long after I joined one of the weekly comics. As a fresh, bright-eyed young journalist I was a little overawed by being sent out to collect one of the recently introduced R75/5 BMs for test.

Chas soon brought me down to earth. He didn't reckon it was a real BMW. Not a proper one anyway. Not like the ones they used to make, or the ones they could still make, if only . . . Well we all have to learn to face new things. Though we don't always agree with way they turn out.

But Chas Isn't just one of these people who's always harping on about the old days. He's just got very particular ideas on his motorcycles. And they make a of sense. In fact, the more I think about them, the more sense they make, whether by long experience, or just an awareness of the natural order of things. One of the prime rules, for example, is that you should always mount a motor­cycle from the left hand side, like a horse. And there were plenty for rules that applied to BMWs especially. For instance, the approach to the parked vehicle.

You should never sit on it and push it off the stand. You first lean over it, roll it off and swing your right leg across, remembering, of course, to give the mainstand spring a little urge with your toe. It's particularly important to do that from the side after the first few months of a new bike, when the little metal prong has broken off, and you have to hook your foot right underneath. It's little touches like that which are reassuringly similar about all BMWs whatever their age, colour scheme, or specification. There's no other marque which manages to retain so may quaint idiosyncracies in its pedigree.

Chas taught me most of what I know about those mysteries. How to use the clutch and change gear properly, how to deal with brakes that always squeaked, and tappets that always rattled. The sense of what he said is as true and familiar now as I reflect on the 1977 BMW/7 range as it was then when I collected my very first 750.

Eight models and 40,000 shaft-driven miles further on, it's hard to avoid the summary that the most striking thing that's changed has been the price. With another speed in the gearbox, and a disc brake on the front, this year's 750 cost just a thousand pounds more than the one I rode five years ago, and the new top model of the range, fancy fairing, instruments and all, almost a thou more again.

BMW pulled off something of a coup with their RIGORS (remember to keep these letters in the right order or the next few pages will get confusing), with its wind tunnel designed integral streamlining, ergonomic cockpit, 18 per cent better time keeping, and yes, I know, you've read all that before. BMWs sales drive, based on their pride of the line has rather over­shadowed the 1977 models of previous range leaders, the updated 750 and uprated R100S (which has superceded last year's R90S).

There are a host of detail changes to both bikes, as well as more subtle cosmetic changes. But the most obvious difference is the move up to a full litre on the top models. This has been achieved by stretching the bore out 4mm to give an actual capacity of 980cc, a simple enough move, but the resulting oversquare power unit is radically dif­ferent from it's fire-eating predecessor.

Instead of increasing out and out performance, the consequence is been altered as perfected. There was never a great deal wrong with the 750 BMW. It did need five speeds to keep in line with the performance of its con­temporaries, but problems with the ear­lier boxes left the gear change generally stiff and more temperamental than even the legendary clunk-click machine could condone.

The new cluster is just perfect. In fact the 750 I rode had the best gearbox of any BMW I've known as far as smooth selection goes. Tshe secret is to feel your way through, but forcefully, without fear of dramatic noises. They're just there simply to inform you the dogs have connected. On previous models a shy toe could result in incorrect mesh­ing, and all sorts of nasty complications. The new ones seem fuss free, and relatively foolproof. One up for progress.

The single front disc with its floating caliper and perforated surface is also by far the best arrestor of any current motorcycle for its combination of adequate stopping power and maximum feel. What it loses in absolute force to twin discs, it gains in precise control at the fingertips. And those engaged in lengthy debate on the efficacy of discs on two wheels would do well to chew on this one before pontification. Gentlemen, we have the technology ...

BMW's system of a cable operated handlebar lever leading to a master cylinder out of harm's way beneath the tank loses no efficiency for its extra mechanics.

Moreover, I felt much happier with the single disc on the 750 than I did with the twin setup on the 1000. In comparison, they felt very spongy, and did not inspire the same trust and predictability in regular use.

Among the many internal improvements to the big, flat twin engines, attention has been given, to one of BMW's nagging failures, oil seepage. This either causes excessive oil consumption, or a fine mist appearing on external surfaces, especially at the base of the barrel.

The driving force for these gushers is crankcase pressure. BMWs have a relatively small wet sump capacity — just 4 pints — and lubrication is consequently fed with some power to ensure comprehensive circulation. As a result, a small leak is liable to become a big one. However, new '0' rings at the stem of each pot, and improved crank- smoother torque curve which has com­pletely flattened the great power step that used to launch the 900 forward like a demon. Gone is the thumping power of the old 'S', it is more lazy and less exhilarating, and rather mimics the characteristics of its smaller stablemate.

My immediate reaction was one of disappointment, verging on nostalgia. While a lot of other things make the R100S a nicer bike, it has rather lost its spirit, in the same way it has relin­quished its flamboyant two-tone colour scheme. The paint work is immaculate, but the dainty gold trim line on the tank is a poor substitute for more exotic metalflake. No, they don't paint 'em like they used to.

Instrumentation remains basically the same, the small cockpit fairing concealing a voltmeter, and almost certainly the most valuable addition to the dashboard, a clock. I can't understand why, of all those gadget-minded people in the accessory business busy bolting on other goodies to standard road machines, no one else has seen fit to market a time­piece. Far from a fruitless status symbol, it is a constant boon to well-wrapped wrists, with inaccessible watches.

With typical teutonic thoroughness, it is quite reliable, and runs of course, independent of the ignition. In addition to the cockpit console, the R100S retains the same rev counter and speedo as all models, together with neutral lamp, main beam and flasher indicators, generator warning light, and the extraordinarily excessive one marked ominously 'brake failure'. This meters the fluid level in the master cylinder, although its label looks disconcertingly dramatic.

That, in any case only applies to the twin discs at the front, with the bike sticking faithfully to the perfectly pow­erful and predictable rear drum.

The final point of distinction is the nicely shaped dual seat, with a rear hump concealing a handy storage area underneath the tail. This seating accommodation is one of the fruitful advances, though the side folding fittings, which never quite seat fully, remain. This means that unless, like a hardened BMW traveller, you pack the underside with something like an oversuit, it will probably rattle a bit. Obviously they only put them in a wind tunnel front first.

In comparison with the rather detuned S, the R75/7 has not so much case ventilation may have worked the trick. Certainly neither test bike showed any external wounds, and oil con­sumption was negligible.

Also inside there are modified rocker arms, higher tolerances on the valve springs, and lighter aluminium tappets, all of which result in smaller valve clearances, and consequently a quieter note from a traditionally 'tappety' en­gine. The finning on the barrel is also shorter and thicker, again helping to reduce resonance. They don't sound quite like they used to either.

The handlebar switches have again been modified because of criticism that previous ones were too fiddly to operate properly in action. What they've done is to add a wing extension to the up-and-down thumb controls either side. On the right, the indicators, the other the lights. Unfortunately on both my test bikes, I found more difficulties than before. The dip switch went down fine, but flicking up again to main beam proved awkward, and tended to jam, while, on the other hand, great care was needed after turn­ing to prevent switching from one indi­cator to another. The performance of the lights when selected however, was ex­cellent.

For some reason BMW have a tradition of eccentric key design which began back in the old Bosch toggle days, and the current offering maintains the line. The shaft is conventional enough, but with a folding head, it is tricky to handle, unnecessarily awkward to use, and impossible to insert in the seat lock.

That is particularly unfortunate because without security the tool tray with its immaculate 23 piece set and roll, puncture repair outfit, and handpump are all prey to prying fingers. The seat, if locked, also serves to secure the simple but effective helmet holder, so it is a necessity.

I can vouch for the tool kit as I have actually once seen and used one in the past, though it's a sad comment on the declining standard of motorcycle jour­nalism that BMW evidently no longer trusts to send its test bikes out with such a tempting and removable selection.

BMW also, for some reason, seem to have lost the ability to make petrol caps. The ones on the last models kept pop­ping open at the most inopportune moments. Perhaps in frustration, they've now abandoned the concept and merely borrowed what look like stoppers for oversize hot water bottles. Flush with the tank, they are difficult to get out, and impossible to tighten on a large thread. Forget any ideas of a tank bag unless you don't intend to refuel.

On the external side of the engine, noticeable changes are the streamlined rocker boxes in matt black, surmounted by monster rubber suppressor caps. The R100S also has new 40mm Bing carburettors, and while these pose yet an increasing hazard to the shins (padded boots are advisable), they give an im­pressive performance, and have ironed out a lot of the more erratic breathing of the 90s. Cold starting with the beefed up starter motor was reliable — just as well as they've long since abandoned the kick start you couldn't kick anyway. A brief warm up, and a certain hesitancy for the first mile or so was the only demand made upon the throttle.

Such is the smoothness of the new R100S power that you can't really tell it from the 750 'til you get up over 5000rpm. Then the torque shakes the mirrors to a blur before it eases out to a gently throbbing 4000 to give you your legal limit cruising speed.

The power in hand above and beyond that is the main clue to the near full litre power source you're sitting on. But it never surges, it just rolls on and off.

Handling of the 750 was impeccable, and tuned to its slightly less momentous power. What you don't have in sheer horses, you can maintain by keeping the motor turning and letting the finely balanced frame and suspension do the work.

The R100S however, despite its smooth power band, proved to be even more a handful than the R90S used to be. More, perhaps because of its decep­tive nature. It was not so well disposed to change determined direction, and more inclined to wave its head over the bumps. Disconcerting rather than actu­ally dangerous. You'd never quite lose control of a BMW, it just keeps you very wide awake.

Perhaps in its relative instability, it proves the claims for the more futuristic RIOORS, and the exotically sculptured full fairing. If the aerodynamics of the RS keep the front wheel more firmly on the ground, if only by the standards of the S you can judge it, and the case seems creditable. Although it has 5bhp less, the S is a little lighter, and a shade quicker than the RS, but it has perhaps the speed at the price of security.

And unlike the RS, it doesn't have a steering damper, a device which has always been of uncertain value to BMW geometry, and at times a positive nuisance.

What you do get is a bike with a top speed of around 118mph, which will do a standing quarter mile in 14 seconds and average about 45mpg. The 750, in com­parison will take about 16 seconds to cover the distance, and levels out at around 104. Reasonable performance figures without being sensational.

And that is perhaps BMW's hallmark. The RS apart, there is nothing that sen­sational about BMW's new range. Nothing in fact that hasn't already been remarkable about these machines for many years.

In many ways some of the additions and alterations have rather gilded the lily of an extremely well thought out and excellently engineered motorcycle. It's just sad that the gilding has been at such a cost that the secrets of how extraor­dinarily enjoyable motorcycling can really be will be reserved for a privileged few.

BMW R100S (R75/7) Specifications

  • Engine: 980cc 94 x 70.6mm (745 cc 82 x 70.6mm) horizontally opposed flat twin. Overhead valves 44mm (42) inlet. 40mm (38) exhaust. Light alloy cylinder heads and barrels. Cast iron liners. Two plain main bearings. Plain big ends. Wet sump lubrication capacity four pints with replaceable paper filter. Two 40mm-choke Bing constant velocity car­burettors, with cable-operated cold start jets. Paper element filter. Compression ratio 9.5 to 1. (9 to 1). Claimed power max. 65bhp at 6,600rpm. (50bhpat6,200rpm).
  • Transmission: Dry single-plate clutch mounted on crankshaft. Helical gears to five speed box. Ratios: 4.4, 2.8, 2.1, 1.6, 1.5 to 1. Shaft final drive ratio 2.9 to 1. (3.2tol) No kick start.
  • Electrics: Coil ignition. 12 volt 28 amp-hour battery. 240 watt (280 watt) alternator. 7 in diameter headlamp 60/55 watt main beam. Five fuses. Electric start.
  • Brakes: Cable and hydraulically oper­ated twin front discs (single). 1014in dia. 7% in drum rear.
  • Tyres: 3.25 x 19in front. 4.00 x 18in rear.
  • Suspension: Telescopic front. Hydraulic and spring rear with three position ad­justment.
  • Wheelbase: 5814in; seat
  • Height: 3H/2in (30y2);
  • Curb weight: 480 Ib (460 Ib).
  • Fuel capacity: 5*4 gallons including 5 pint reserve.
  • Price: £2,659 inc VAT. (£2,179).