MODS & SHOCKERS

If you have an airhead or plan to buy one, a couple of Ian’s upgrades might improve your ride. Starting at the front of the machine:

TWIN DISC FRONT BRAKE:

Mentioned in the text. The cast wheel arrived at this time too, and while I did plan to refit the spoked one, it works as-is so that never happened

HIGH CAPACITY ALTERNATOR.

Probably not needed, but provides reliable heated grips and loads of spare capacity should it ever be required

ELECTRONIC IGNITION.

The bike’s now on its third version. One failed, and the ECU was replaced. I suspected the replacement was going the same way, so changed to a totally different system

STARTER MOTOR.

The original Bosch is heavy (cast iron), low powered with electromagnets and has a high load in use. The replacement Valeo item is reputedly 6lb lighter, is easier on the battery and turns the engine over much more freely. Starting is now instant. Beware though, early bikes like mine need an 8 tooth bendix compared to the 9 tooth one fitted to these starters when they became standard fitment on the lighter flywheel airheads

VALVE GEAR.

BMW valve gear rattles; period. Valvegear went through three versions during the airhead’s lifetime. Late models have shimmed rockers to reduce end float, but this cannot be fitted to early bikes like mine without machining. The noise absolutely did my head in, so mine has been modified to accept some rather trick one-piece CNC machined rocker mounts from a German company, Motoren Israel. They still rattle, particularly when cold, but nowhere near as much

TWIN PLUGGING

and hardened valve seats. Modern petrol and a long flame path are not a good mix. It’s probably fine if you plan to tootle gently around the countryside in true classic bike mode, but if you like to use your bike as intended, then these mods might be worth thinking about. One of the original twin outlet coils that were supplied with the mapped for twin plug ignition failed, so the bike is now fitted with Dyna Coils (Two 1.5 Ohm coils wired in series)

GEARBOX.

Later, stronger version fitted

SWINGING ARM.

While still at the twin-shock stage, BMW decided that a shock absorber in the drive shaft would give the gearbox an easier time. They are a direct bolt-on replacement for the swinging arms on earlier bikes, and since gearboxes are expensive, why would you not fit one? The shaft side of the swinging arm is of larger diameter tube to allow for the shock absorber, which prevented me from using the original brake light switch

SEAT.

The original seat base rotted away, so was replaced by a pattern one. The cover on this quickly ripped, so I tried another; originally a Corbin item that soaked up water profusely. Because of the waterlogging problems, I had it re-covered without the king and queen profile which I disliked anyway. It’s not as pretty as the original seat, and it adds an inch or so the ride height, but it is comfortable. I may change it again at some point, but it is low on the priority list

GIVI PANNIER FRAMES.

The bike came without luggage, which is unusual for a BM. A secondhand Givi rack was a whole £10 at the time (originally for an old Goldwing), and was modified to fit by friend and ace welder Red. I had one luggage box already and picked up a few more over time. The seat has been modified to lift off rather than hinge, to clear these frames

REAR DIFFERENTIAL.

Changing the gearing on a shaft drive bike will always be problematic. My R75 constantly felt to me like it was under geared, like there should have been a sixth gear in there to make it a more leisurely road burner. I fitted the differential from a 900cc bike when I got the chance, and now it purrs at 70 rather than buzzes. As for speedo accuracy, comparing it now against a sat nav, the mod seems simply to have reduced the rather optimistic speedo to a more realistic reading