Motorcycle Repair: 1985 Harley FXST 1340 Primary Lube, harley fxst, sae 40

Question
Roy, Can you tell me what lube should be used on this bike in the primary? It has a chain drive primary.  Is it OK to use automatic trans fluid? I was told I could but wanted to be sure. Thanks, Andy

Answer
Andy I would not use auto. trans. fluid in your primary.  It's too lightweight.  Harley's primary chaincase oil which they came out with in 1984 for the Evo motor is actually a single weight oil, more like SAE 40.  You should use HD primary chaincase oil or an aftermarket oil like Spectro Golden Primary Oil or Drag Specialties Primary Oil.  You need a heavy enough oil for proper lubrication of the bearings and primary chain, but not too heavy for the clutch.  Just spend the extra few bucks for a specific "primary chaincase oil".  You can use the full synthetic like Syn-3 from HD or Mobil-1 20-50 full synthetic Motorcycle oil but they cost like nine bucks a quart.  The best is just to use any good brand that says it's for big twin "primary chaincase" applications.  Incidentally, back then they recommended 40 oz., then dropped it to 32 oz. and now they use 26 oz. in the primary.  I think they found too much clutch slippage, although the clutch ran cooler.   I think 26 oz. is plenty.