Tune Up a BMW /5 Airhead Engine

Reader Contribution by The Motorcycle Classics Staff
Published on April 13, 2015
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Last time, we showed you how to adjust the valves on a BMW /5 airhead twin. Valve adjustment is the first step in a comprehensive tune up, followed by replacing the ignition points, spark plugs, air filter, and setting timing. While replacing ignition points and setting ignition timing can be a laborious process on some bikes — Kawasaki triples spring to mind — it’s extremely straight-forward on BMW’s /5 twins.

A few points are worth noting. First, never remove the front engine cover without first disconnecting the battery. On /5 airhead BMWs, the alternator is located directly behind the front cover; if the battery’s connected you can potentially short the alternator by grounding it with the aluminum cover.

Secondly, if you need to rotate the engine, never try to spin it using the 10mm nut on the automatic advance unit: There’s a high probability you’ll snap the threaded snout, which is an extension of the camshaft. Instead, use a 6mm Allen wrench in the end of the alternator, and even then make sure the spark plugs are out so you’re not working against compression.

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