Motorcycle Classics Blogs wrote:
MC How-To
BMW /5 Charging System Upgrade
10/27/2016 12:00:00 AM
By the Motorcycle Classics staff
As good as BMW’s classic /5 series is, there’s always room for improvement. One thing old /5s — and just about every airhead from 1970-1994 — can really benefit from is a charging system upgrade. While the stock system basically works fine, it can come up short in voltage delivery, especially in low-rpm urban situations where the engine doesn’t spin at high enough revolutions to maintain the necessary voltage to keep the battery up.
Euro MotoElectrics in Denver, Colorado, specializes in electric system upgrades for BMW, Moto Guzzi and Ducati. Over the years, they’ve developed numerous starting and charging kits for vintage and contemporary BMWs, including the EnDuraLast III kit for 1970-1977 airheads.
The comprehensive kit includes a new 4-wire stator plus a new rotor, diode board, diode board mounts, alternator brushes, an adjustable voltage regulator and wiring. The major benefits of the system are increased output (240 watts versus 180 watts stock), with charging voltage coming on at significantly lower rpms than the stock system.
For our BikeMasterinstall on a 1973 R75/5 we also had Euro MotoElectrics send us a new front crankshaft oil seal (easy to do while you’re there) along with a rotor removal bolt and an optional resistor lead for the charging light. The charging light excites the system, but if the light fails the system won’t charge. This simple modification is just a safeguard in the unlikely event the charge light does fail.
This is a high-quality, well-thought-out upgrade and everything goes together exactly as it should. That said, we suggest making this a weekend project to give yourself plenty of time, as it is fairly involved for the average weekend warrior. Required tools include a good soldering iron and solder/flux, a torque wrench, and, if you replace the crankshaft seal, a seal puller.
Depending on the exact year of your bike, you may or may not have to install an insulated Y-post connection for the upgraded 4-wire stator. The extra wire — added starting in 1974 — increases the efficiency of the AC to DC conversion. We forgot to order the available kit and came up with our own Y-post, a 4mm bolt with mylar for insulation. Simple enough, but the optional Y-bolt kit from Euro is only $2.75 and worth getting. That brings us to cost, which we consider very reasonable given the improvements gained (more on that in a second). The complete kit goes for $350, with the rotor tool adding $8.25, the seal $7.95 and the charging light circuit mod another $20, for an all-in of $388.95 if you also get the Y-post kit. By comparison, a replacement BMW rotor and stator alone will set you back almost $500.
As for performance, our system went from barely producing 13 volts at 4,000rpm to kicking out 14.25 volts as low as 1,500rpm. That’s an impressive improvement, ensuring full charging even if all you do is lope around town. As ever, we suggest having a good manual on hand for parts identification and proper torque specs.
Continued here
--John
