I work for an oil company and even I'm confused over this:

Currently running Syn3 in both the engine and gearbox (as recommended) but fancied trying the new Formula + gearbox oil.

Local dealer told me that HD don't recommend using Formula + with Syn3 up front. Only Formula + with mineral engine oil or Syn3 with SportTrans or Syn3 in the back.

They didn't know why and nor do I.

As they don't mix I am confused.

The only reasons I could work out was if Formula + is Ester based and if a leak into the engine compartment happened (don't know if this is possible even) the two oil types are incompatible and could cause problems or if there are extreme running temperature differenced between the various fluids (unlikley).

Any one have any info / ideas?

got me..


hang on a sec.....just had a thought...


The front engine seal on sporties is the opposite way around to big twins.....

sporties can vent some of their engine gasses into the primary which will vent out of the gearbox breather tube under your seat....

One of the reasons I'm not a big SYN fan is because I have seen failures from incompatibility of oils..


Myabe that's what they're on about...