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Bike Review - Posted 10th February 2014
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1979 BMW R100RT

Most riders have nothing but good things to say about air-head BMW Boxers. However, Doug Almond's experiences haven't been completely positive...

I was very interested in the article by Andrew Shortridge back in the October 2013 issue of RealClassic magazine. It is the first time I have seen well deserved, uncomplimentary, remarks on BMW design. I am the unlucky owner of a 1979 BMW R100RT. This is what was known as an 'interim model', in other words a stop-gap while the designers thought up something better. The design brief was probably; 'stop those amateur spanner throwers on that island over there from abusing our products.' I think it only survived for two years, but they probably sold at least half a dozen.

Andrew mentioned the infamous cable-operated hydraulic front brake with its master cylinder and reservoir under the fuel tank. This has been mitigated (at a price) by a conversion kit to move the master cylinder and reservoir on to the handlebar. The brakes, which are twin ATE swinging calliper discs, are quite effective when you have spent a day or so setting them up. However the design ingenuity does not end there.

1979 BMW R100RT

In order to perform the nominally simple task of changing the battery there are two choices. The first is to remove the seat and fuel tank and dismantle the huge air cleaner assembly. The second is to release the rear section of the frame and jack up the machine from under the engine, allowing the rear frame section to drop down. Mine is a sidecar outfit which negates use of the centre stand. The battery carrier can then be unbolted and allowed to swing backwards, enabling the battery to clear the carrier.

1979 BMW R100RT

In order to adjust the free play on the rear brake pedal, first remove the right hand silencer. The same two bolts hold the brake assembly, which cannot be seen. Release the master cylinder and the brake assembly and when dropped down clear of the frame, the adjustable link can be disconnected and adjusted. In order to check whether the adjustment is satisfactory the whole assembly must be replaced. Any further adjustment requires the same procedure to be followed.

1979 BMW R100RT
R100 BMWs on Now...

The rear brake on this model is a single disc Brembo. It is basically a not very attractive decoration. Its stopping power is in the 'block in a belt pulley' class. I have replaced the disc, the master cylinder, the calliper and the pipe work. It seems to be impossible to get the air out of the system. I have pumped gallons of hydraulic fluid through the system, by both the traditional method and using a pressure bleeding kit. The normal method fails because the master cylinder does not have enough capacity to push the fluid from the reservoir to the calliper, it just surges back and forth in the pipe.

The pressure seems fine until it is disconnected, when the spongy loss of brake pressure returns. I've tried the trick of removing the calliper assembly and bleeding the brake with the calliper upside down. A couple of years ago, before they closed down, I rang the nearest official BMW dealer to ask for any ideas on improving the rear brake. Their advice was to convert to a drum brake. On the plus side, a few years of having a 650 AJS on the chair teaches one to ride a combo without brakes.

1979 BMW R100RT

Another charming but fortunately infrequent trick is for one of the Bing constant depression carburettors to suddenly flood. Since they are situated immediately above the exhausts there is a distinct possibility of the rider doing a passable impression of Guy Fawkes.

In July last summer I rode up to Mallory Park for the VMCC Festival. On the way home, on the hottest day of the year, the engine lost power and was as rough as a bear's rear anatomy. After 150 miles I stopped for petrol and the engine would only start on full choke. I nursed it for the rest of the 250 mile journey, which took eight hours. The next morning it would only run on one cylinder. Two months later and I have tried new points, new condenser, new coils, new plugs, new carburettor needle and gaskets, and new plug leads. I've checked the compressions, the vacuum readings, the timing and the exhausts. I have now managed to borrow a left hand carburettor to try. The left hand cylinder is still as dead as a dodo.

1979 BMW R100RT

I've had the outfit for seven years and apart from the dodgy adjustment systems and the lack of a rear brake it has covered over 20,000 trouble free miles. Its cruising speed and load carrying ability make it an excellent tourer. In almost 70 years of motorcycling it remains my only defeat…


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And for an alternative view of a 1979 R100, read Part I and Part II of Martin Gelder's R100S tale


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