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What about the marks F, OT, S, Z that are on your Flywheel (clutch carrier)?

F,OT,S,Z.htm
39

 

OT is Top Dead Center, that point, exactly, when the pistons are fully outwards.   OT, in German, is Oberer Totpunkt, more correctly translated as the top dead point.  

The PRIMARY, or most often used reason to find OT, is for setting the valves.  NOTE that the pistons in airheads are TWO ''strokes'' away from each other.  You MUST set the valves with the particular cylinder being adjusted, at the OT mark ...AND!!....THAT cylinder must be on ITS COMPRESSION stroke.

A common use for OT is for setting the ignition timing on some (some use the S mark) dual-plug converted engines.     When installing a timing chain or crankshaft or camshaft sprocket, we use the OT mark as a reference.   There can be other uses. 

The S mark is the Static timing point, that is, no rpm or low rpm, and the S stands for Spaetzuendung (minimum advance; that is, late or retarded).  

The F and Z markings are basically the same. The F (the depression dot) and the Z marks are for the maximum ignition timing advance point.    The F really stands for Fruehzuendung (spark advanced).  On our airheads, the F dot (or, Z marking, later bikes) is seen (via spark triggered strobe light) by raising the rpm until the timing no longer continues to advance, this point is about 2000 rpm on the early /5 models, and 3000 on models after that.   There are a number of mechanical advance versions, so if your /5 maximum occurs at 3000, don't be alarmed.   

Rev.:
01/18/2008:  from article 40; to a new page here; and edit for clarity

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