I recently purchased a 2007 HD Fatboy with a stock 96 cube motor. I don’t know what oil was in the bike, but it had 9,300 miles on it. I recently changed the oil to Amsoil 20w-50 Motorcycle and immediately noticed a smoother running engine and a much cooler running engine. I would give the oil 5 of 5 stars no matter what was in it before.
After reading an article from a professional bike builder with lots of dyno and race experience, he convinced me that Red Line Heavy full synthetic Shockproof gear oil was worth trying as a transmission replacement lube. His testimonial was, there is nothing better. According to the bottle, the lube is equivalent to 75w-250. My bike takes 24 oz., so I ordered two quarts, (one for my brother’s `06 Harley) from Jeg’s High Performance at a cost of $33.90 with no shipping charges. After the change-out and a few short trips up and down my road. I noticed the gears meshing much smoother as I went. Biggest noticeable difference though was my ability to find neutral which I figure was 200% easier and that alone made the $17 expense worth it. I would rate this gear oil 4 of 5 stars which may not be fair, because the shifting still isn’t as smooth as I would have hoped for but this could simply be as good as this HD transmission gets?
Next up, will be a handlebar change along with a new shield of some sort.