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Bike Profile - Posted 8th June 2012

1977 BMW R80/7 - Part 12 - Going, Stopping, Standing
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A new clutch, gearbox, driveshaft and final drive. New paperwork from the DVLA. New brakes. A new sidestand spring, even. Martin Gelder is preparing his 980cc R80/7 airhead BMW for a big trip...

It's been a while. Nearly a year. At the end of the last episode I'd just completed the first 1,000 miles aboard Roxanne the BMW R80/7 since she'd been fitted with R100 barrels and pistons, bumping the engine capacity up to 980cc. Initial impressions were all good; significantly improved throttle response and pulling power, unchanged fuel consumption, slightly more vibration... and a slipping clutch.

Clutch, Drive

Airhead BMWs sandwich their single plate dry clutch between crankcase and gearbox, making a clutch plate swap a non-trivial task. And I only had one day to do the job, having planned to camp overnight on the way to Founder's Day the day after returning from the Compass Challenge . In for a penny, in for a pound, I decided I might as well replace the whole transmission with the lower mileage one from The Vicar's Bike, the R80 I had bought to break for spares, while I was at it. Eight or so hours later I had a bike with a brand new clutch plate and a less tired gearbox, shaft, and bevel box.

Replacing the battery is only slightly more complicated than changing the clutch...

The donor parts came from a 1979 bike, that being the first year that the drive shaft was fitted with a sprung shock-absorber. I didn't know this until I took my post-rebuild test run round the block; there's a very subtle difference in feel when drive is taken up and then a more noticeable change when the throttle is closed and the shock-absorber unwinds. The replacement gearbox was a real improvement, with crisper changes, and although the new clutch was initially very grabby it refused to be provoked into slipping.

The next day. Much improved...

--- There will now be an intermission while I use the BMW as my winter hack ---

Time passes, miles mount up, but the BMW continues to rumble on. The vibrations ease somewhat, and shifts slightly further up the rev range. They're at their worst at around 75mph, but push through that speed and all becomes serene and calm at around 90mph... the point at which the high-barred riding position patently doesn't work. Lucky, then, that all of this only ever happens on private test tracks. Ahem.

Stop, Stop

With great power comes great responsibility. And the need for great brakes. Or at least better than barely adequate brakes. Standard issue R80/7 kit is a single stainless steel disc, with a single piston "swinging" ATE calliper worked by a master cylinder hidden under the tank and in turn actuated by cable from a conventional handlebar lever. My bike had already been fitted with a cast iron disc and a calliper rebuild had produced effective if not inspiring braking.

Lurking in the shed, the remains of The Vicar's Bike...

Lurking in the shed, though, was the twin disc front end and handlebar mounted master cylinder from The Vicar's Bike. The master cylinder conversion uses parts from a later model airhead, and replaces the under-tank gubbins with a simple splitter block for the hydraulic hoses and a compact hydraulic master cylinder which mounts on the bars. Less crash-proof, but with less opportunity for wear in the 'brake train' to steal feel and effectiveness.

Now fitted to Roxanne...

The fork legs were a straight swap into the original yokes, the pair of (also cast iron) discs bolted to the original wheel in place of the previous singleton, and the end result was... better than expected. Twice as many callipers biting on twice as many discs doesn't always guarantee twice as much stopping power, but the handlebar mounted master cylinder increases the feel at the lever significantly, meaning that although the braking still isn't in the same league as my Morini or modern Yamaha, the brake operation feels more consistent across the three bikes. This has massively improved my confidence in the bike's ability to stop, which is half the battle when it comes to brakes, in my view.

Different length, different strength...

Stripping Roxanne's original forks also revealed a "feature" which can't have helped her sometimes flouncy handling; two different length and apparently different strength fork springs. She now has a matched pair of progressive springs which are perhaps a little soft, but at least both legs are working together rather than against each other.

Papiere, Bitte

Changing a bike's engine capacity means changing the information on the V5C log book, so I filled in the new "new engine capacity" box on the V5C and posted it to off Swansea. A couple of weeks later, the new log book arrived with the new capacity listed. Simple.

Or not. A further couple of weeks later, I got a letter from a man called Gregg VC9 D4, asking me for "one form of evidence from the list below" to prove that I really had changed the engine size. He then went on to list five choices which did not apply to me, as I had - horrors - done the work myself.

What Gregg VC9 D4 wanted - basically - was some form of documentation from the company that had done the conversion for me. The thought of someone having done something like this themselves, using second-hand parts for gawd's sake, wasn't catered for.

The best I could come up with was Mr VC9 D4's final option, "written confirmation of the change on headed paper from an independent garage", which my local bike shop Wheelfit were happy to provide, presumably because I've been a regular customer for a dozen years.

Big Trip BMWs on now

The letter went back to the DVLA some weeks ago, and at the time of writing I've yet to hear anything. I can't help thinking this is the thin end of a wedge which will see significant engine work done by the home mechanic gradually marginalised. "You can do your own work, but we want proof from a grown up before we consider it done."

Spring, Sprung

One of the perils of using a 35 year old bike as everyday transport is that no matter how carefully maintained the bike, age will eventually - and sometimes quite suddenly - take its toll on some parts. Usually at the most inconvenient moment.

It shouldn't have been a surprise, then, when Roxanne's sidestand spring snapped at the very moment that I was about to set off on a 160 mile journey. Bike loaded, earplugs in, helmet on, gloves on, engine started, and... tink. Sidestand lolling, spring dangling, departure delayed.

I thought I had a spare, but half an hour's rummaging produced several centre stand springs - new and used - but nothing suitable for the side stand. Still, Molegrips are your friend in situations like this, and with the help of two pairs of them I managed to fashion a hook out of the stump of the spring and we were off.

Two sidestand springs, yesterday...

Fitting the new spring (ordered online from Motorworks and delivered next day) was one of the most difficult jobs I've had to do on a BMW. Eventually, by inserting 'pennies' - actually Euro 1 cent coins, the slimmest I could find - between the coils of the spring I managed to extend it enough to allow it to be hooked into place.

I knew those 1 cent coins would come in handy for something...

Doing this needed both the side stand and centre stand to be retracted, which meant laying the bike on its side in a most undignified manner. And then I realised that I'd used one of the centre stand spring (there are two) mounting holes instead of the correct side stand one. It had been such an almighty struggle to get the blummin' spring in place that I decided to work on the "if it ain't broke" principle and simply carry a spare centre stand spring in the tool tray.

Paddock stands and work benches? Who needs 'em...

One of that day's decisions would later come back to bite me...

Words and Photos: Martin Gelder

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  • Motorworks - Quick online parts delivery.
  • Wheelfit, Cambridge - Nice people. Support your local independent bike shop.

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