1977 BMW R80/7 - Part 3 - Classic Motorcycle Guide

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1977 BMW R80/7 - Part 3

MOT time for Roxanne the BMW R80/7 but first there's that business with the red light to sort out, she's a bit moist underneath and her rear end is sagging a little too much for Martin Gelder's liking...

At the end of the previous episode Roxanne (you don't have to put on the red light) the BMW R80/7 had developed a dodgy charging system, but it looked as though a couple of clouts to the electro-mechanical regulator and a good clean up of the contacts between alternator and regulator had fixed things.

The first ride after coming home from the Festival of a Thousand Bikes at Mallory Park saw the generator light flickering back on less than two miles from home. The fix obviously wasn't a fix after all.

Five minutes of poking at the battery terminals with the multimeter I hadn't had to use since I owned a Moto Guzzi showed a voltage of very slightly under 12 volts at tickover, very slightly over 12 volts at about 2000rpm, and very slightly under 12 volts at around 4000 rpm. A healthy charging system should be pumping 13.8 volts into the battery at anything over tickover so either the alternator wasn't generating enough umph, the rectifier wasn't letting enough umph through to the regulator, or the regulator was throwing too much umph away before it got to the battery. Or something. I can remember that my school physics teacher was called Dave Ross and that he was very tall but not much of the electronics stuff he taught me actually sank in.

A bit more probing with the voltmeter showed a lot more voltage going into the regulator than coming out, so that was deemed prime suspect. The wire connecting one of the alternator brushes had been repaired with a crimped connector, so it seemed sensible to replace that as well. A quick call to James Sherlock's in Devon (www.DevonBMW.co.uk) had a solid state regulator and a new set of brushes and their mounting plate dropping through the letter box. They'd advised me that the regulator almost certainly was the problem, but that it wasn't worth going for the "high output" version; the standard one should manage normal charging duties fine.

Changing the brushes and their mounting plate means removing the alternator stator; a large lump of rusty iron and aluminium bolted to the front of the crankcases. In the perfect world of Haynes manuals this is a simple matter of making a careful note of the position of five electrical connectors and then undoing three Allen bolts, taking care that the stator doesn't drop on your toes as it leaps free from the crankcase.

More corrosion inside the alternator cover than outside it...

In the neck-burning, scalp-singeing, sweat-running-into-your-eyes 35 degree heat of a July afternoon in Cambridge 2006, the alternator remained firmly in position despite no visible means of support other than 30 years of corrosion. A couple of gentle taps with the Mighty Thor's nylon headed cousin failed to persuade the alternator to fall into my sweaty hands, so the screws went back in and the connectors were replaced. No point fixing one of the parts of the charging system that didn't seem broken.

Swapping the regulator was much more suited to my Lego-level abilities; two screws with captive nuts and one three pin connector. Time for a cold drink.

Old one on the left, new one on the right.

Shazzam. Just under 14 volts at the battery as soon as the generator light winks out, no change beyond that as the revs climb, and a much more positive blink back on again from the light when the tickover settles back below 1000rpm.

The other problems the run to Mallory had shown up were what seemed to be a worsening oil leak from the bases of the pushrod tubes and a somewhat bouncy rear end due to the damping oil from one of the rear shocks making a bid for freedom. With the MOT looming the shock absorbers definitely needed attention, and message board regular KarlB had suggested a quick fix for the oil leak.

A few gentle taps with a hammer and drift knocked the push rod tube seals back against their seats. I'd given the bike's engine a good gunking to try and isolate the source of the various leaks that were coating the sump and stands with oil, and Cousin of Thor seemed have done the trick. If only more things could be fixed by hitting them with hammers.

Even in good condition the standard shocks and springs on an airhead boxer are a bit on the soft side and the ones on Roxanne were coming up to being 100,000 miles beyond good condition. Last time I had a BMW a set of Koni Dial-a-Rides made a real difference to the handling, and ten years later the same-specification Ikon (geddit) Dial-a-Rides from Motorworks in Holmfirth (www.MotorWorks.co.uk) pulled off the same trick.

The Ikon springs are stiffer than the standard ones and the (adjustable!) damping is better controlled; a real improvement for two-up and luggage laden rides.

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Old one on the right, new one on the left. No putting off the MOT any longer, then. This was my first time under the new "computer controlled" testing regime, and to be honest - and despite the rumours - I couldn't see much difference between old and new tests other than the weighing of the bike for the brake tests.

The fact that the BMW's front brake passed the test tells you more about the low standards required than about the ability of the ATE swinging (groovy baby) calliper and it's pads to slow things down. The only other worry was a couple of cracks in the stainless exhaust pipes around the balance pipe joint, but they weren't judged a problem.

What next? Well, that front brake really does need beefing up a bit, and the tappets are a bit rattly, and…

Sod it. I'm going for a ride.

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