What type of oil is best for the primary case on a 1987 softtail fxst?

Answer 1

"Best" is such a subjective term when it comes to oil, sure to garner different answers from different people.

But I can tell you that in my current personal Harley (my seventh in 42 years), a 1993 Softail, I've used everything in the chaincase from Harley's Formula+ to plain Discount Auto motor oil to Mercron ATF (that's what's in it now).

In over 220,000 miles so far everything I've used in it has worked just fine. No abnormal wear, no clutch slip, no failed bearings, nothing.

Now, I'm much pickier when it comes to what's in the motor or tranny. I run strictly Mobil 1 in the motor and Red Line Heavy Shockproof in the tranny.

But there's not a whole lot going on in the chaincase that requires expensive or exotic oil. All the chaincase oil has to do is lube the chain, the compensator & two bearings plus cool the clutch plates. Pretty much any oil can handle that with ease, especially if it's changed at the recommended intervals.

Bear in mind, Panhead primary chains were oiled entirely by what little motor oil was contained in the mist of the crankcase breather discharge. Evo & Twin Cam primary chains are living large by comparison, constantly and amply bathed in a pool of oil.

However, because the subject of oil is such a highly debated one among those with nothing better to think about, if you have any doubts whatsoever you're probably better off paying Harley nine bucks a quart for their "special" primary oil. There's nothing worse than worrying when you should be enjoying the ride.