Restoration of the BMW R 80 G-S, part 5 chassis and brakes

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Restoration of the BMW R 80 G-S, part 5 chassis and brakes
Cook

Restoration of the BMW R 80 G-S, part 5 chassis and brakes

Restoration of the BMW R 80 G-S, part 5 chassis and brakes

Restoration of the BMW R 80 G-S, part 5 chassis and brakes

Restoration of the BMW R 80 G-S, part 5 chassis and brakes

19th pictures

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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On the left the new, on the right the plate-shaped, warped coupling base plate.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Clutch removal, act five. Wing screws would be handy now.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Powerful, almost snappy: 320 mm disc with delicate four-piston pliers and a larger hydraulic transmission.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Better than the series: 320 washer, floating in connection with the chunky original Brembo caliper.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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The aluminum block between the cardan shaft and the swing arm extends the wheelbase by 50 millimeters: the stability does this without impairing the maneuverability.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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The rear height and thus the steering geometry can be adjusted via the threaded spindle.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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The “weakened” point on the shock absorber mount is only exposed to very low bending forces.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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To make room for the tire, the swing arm was sawed open and closed with a sheet metal.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Lacing made easy: The cardan is a perfect device for lacing and centering the rear wheel.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Spoking made easy: With the Flex, the rusty, stiff spokes are simply cut off.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Only well-lubricated can the braking force be evenly and finely regulated without the slipstick effect.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Small cause, big effect: dry bolts and friction surfaces on the piston impair metering.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Changing the brake fluid is of no use with this oil sludge. The only solution: completely dismantle everything and clean it thoroughly.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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Excess fork oil can be sucked off to exactly the required oil level with a syringe and a rubber hose pulled over it.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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The more (soft) or less (hard) air cushion determines the spring progression and puncture protection.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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With different oil viscosities, the damping of the simply constructed fork can be clearly influenced.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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The length of the shortened spring coils is compensated for by newly made spacer sleeves.

Restoration of the BMW R 80 G-S, part 5 chassis and brakes
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The 0.25 blade fits loosely between the friction disc and the base plate.

counselor

workshop

Restoration of the BMW R 80 G / S, part 5 chassis and brakes

Restoration of the BMW R 80 G / S
Part 5, chassis and brakes

Content of

The engine runs smoothly, everything is fresh and stylish in the paint. Now, our restoration of the BMW R 80 G / S is about getting the chassis going. But not only the budget, but also the clear intention to use as many original parts as possible, forces diligent tinkering with the chassis and brakes.

Werner Koch

05.03.2015

A powerful enduro fork would look good on the BMW R 80 G / S. Tightly braced in fat fork bridges, creamy, dampened, long spring travel, that would be it. I admit, the WP upside-down fork was already ready when the specialist stopped by for a workshop beer and asked, completely horrified: “What are you going to do with G / S? Paris-Dakar? Six Days? Erzberg-Rodeo? ”Uhhh, no, actually a Yamaha WR 250 off-road athlete is standing in front of the door for such excursions. The G / S was to become the pleasure motorcycle in the fleet. Gravel roads, dirt roads, 1.5-tonne road enduro hiking are what they say. 

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And that also works with 170 millimeters of spring travel. Whoops, the WP part disappears back into the spare parts store, instead the original fork lies dissected on the workbench. Quick analysis: The simple, bored damper piston without shims and effective shuttle valves does not allow any great improvements, so it remains untouched. However, the springs, which are simply too soft for a stable front section in the standard trim, are shortened with the cut-off grinder. All tight windings are removed at one end, six “soft” windings remain at the opposite end. After being shortened by 80 millimeters, a 70 millimeter long aluminum sleeve with ten millimeters less preload should keep the BMW R 80 G / S at a level similar to that of the soft but more preloaded springs in series production. 

Shorten the coil springs to make them harder

In general, all coil springs can be made harder by shortening them. And precisely in the ratio in which the available length of the spring wire is reduced. However, this only works if the block value (that is, when the spring is completely compressed) is less than the available free travel. And the springs must be designed to be block-proof, so they must not settle when the stroke is fully used. Shortening the fork increases the spring rate by around 25 percent. And so, just as we had planned for a stable enduro chassis. The nice thing about the springs of the BMW R 80 G / S: The ends are not laid on, but are inserted into plastic sleeves that are adapted to the spring coils, which makes subsequent application with a welding torch and grinding belt superfluous.

When it comes to damping, we use the tried and tested experiment with different oil viscosities and different oil levels in the fork legs. The result: For summery 25 degrees and more, a 15 oil has to be in the fork of the BMW R 80 G / S, if it gets cooler, from around 15 degrees downwards, the damping is too tight and uncomfortable and should be replaced by a thinner 10 -Oil can be made pliable.

BMW R 80 G / S with too little braking power

The air cushion, with which an additional spring progression can be achieved, was adjusted at 180 millimeters. The fully collapsed fork is measured without springs or sleeves. In our tuning, the compressed air above the fork oil replaces the almost entirely missing progressive effect of the standard suspension springs. 

Coordinated in this way, the front of the BMW R 80 G / S braces itself stably and without sagging against even the most massive braking maneuvers. Whereby this is only possible by means of a screw clamp-like access to the lever. Although the Brembo series brake caliper with new pads, high-pressure-resistant line, fresh brake fluid and smooth-running brake lever bites into the 320 disc, the word braking is a bit exaggerated by today’s standards. One could rather say that the BMW slows faster with full braking power. Enough for a forward-looking driving style, too little for the tractor chugging along out of nowhere.

Brembo four-piston caliper from a private collection

So back to the private spare parts catacombs that after three decades of racing spit out many a noble part. A golden Brembo four-piston caliper, originally installed on a Honda RS 250, is installed using an adapter plate made of high-strength aluminum. The inherently better effect is increased by the fact that the hydraulic ratio of the twelve-millimeter hand pump increases from 1:20 to 1: 28.5. Finely adjustable, great effect and even after the tenth full brake application without a break-in, the Heidenau K60 Scout now rubs the lugs off the carcass.   

Raised on the original rims, which were lashed to the hubs by a set of fresh spokes, the East German rubbers drive very harmoniously, with consistently good grip wet and dry and sufficient traction on slippery ground. At full throttle at almost 180 km / h, the wheels of the BMW R 80 G / S stay on track without swinging or swinging.

Stable straight-line stability thanks to the extended swing arm

The stable straight-line stability is certainly also thanks to the 50 millimeter longer swing arm, which has now increased the wheelbase to a solid 1525 millimeters. However, the swing arm had to be cut out in the area of ​​the tire shoulder and closed again with a welded metal sheet. This made it possible to dispense with the off-center spokes of the rear wheel rim.  

Another positive effect of the long swing arm: the static wheel load distribution now puts more pressure on the front wheel, a method that basically ensures more calm at high speeds. Not to be forgotten: the harder fork springs keep the front of the BMW R 80 G / S higher in dynamic driving mode, which means that the caster is longer and the steering head is flatter. So that the stabilizing measures of the G / S do not lose their refreshing maneuverability, the simple Wilbers spring strut type 630 Road with length adjustment was ordered. This means that the geometry can be balanced in no time by raising or lowering the rear section.

Whereby now one or the other classic enthusiast is wondering whether you shouldn’t simply move an almost 35-year-old BMW with all its weaknesses and quirks appropriately and in accordance with contemporary technology, instead of shooting around with it? The answer is clear: both and. The MOTORRAD Classic project, however, is intended to increase the fun factor that is typical of boxers a little and to switch off the less praiseworthy features without depriving the BMW R 80 G / S of its fundamentally honesty and down-to-earth mechanics. Therefore no WP fork, no ignition map, no edgy, modern enduro plastic. When the going gets tough, the R 80 G / S can therefore be upgraded back to its original state with the original parts. 

Moral of the story: Don’t skimp on the boxer clutch!

But I’m not wasting a thought on that at the moment. After almost 6000 kilometers, the fun with the G / S boxer does not diminish. On the contrary: with every move more, the optimization through constant tinkering and screwing turns the BMW R 80 G / S into a favorite in the private fleet. I learn to appreciate the strengths – and to ignore the weaknesses!

The clutch, for example. Because the brave Swabian holds his money tightly together, every investment is considered twice. With the comment, “Ha, it still does!”, Which is very common in Swabian, the 114,000 kilometer old clutch of the BMW R 80 G / S was given a new friction disc. With the result that the clutch was back on the workbench 200 kilometers later. After meticulous measurement and cleaning, the pressure plates were then only fitted with a new disc spring, that has to be enough.

I thought. When the gearbox, now asleep, was lifted out of the chassis for the fifth time, the secret came to light. The firmly screwed pressure plate had warped in the shape of a plate (3/10 mm), the friction lining only carried about half the surface. The friction surface, on the other hand, was in a deceptively flawless condition, with no wear, no blue heat stains and absolutely flat. Sure, the friction disc would have adapted to the plate-shaped deformation over time, especially since the clutch only slipped when it was cold and at maximum acceleration. But a half-life clutch has no place in an everyday motorcycle, that’s that. 

Now the thrifty Swabian has gotten rid of his money for the complete clutch after all. And the moral of the story: Don’t skimp on the boxer clutch! A complete overview of the costs, the specialists and the G / S scene can be found in the next part of the MOTORRAD Classic series “Restoration of the BMW R 80 G / S”.

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