Does the Nighthawk have a wet clutch? If so, you need to be careful using automobile oil. Most standard automobile oils have friction modifiers (it will say Energy Conserving on the API logo) that make the oil slipperier and can cause the clutch to slip.

Chances are you can use standard 10W-40 oil. I've been using Mobil-1 MC-specific synthetic oil and I'm happy with its performance. However, it is a bit pricey. I'm thinking about trying some Castrol Syntec 10W-40 (their 10W-40 doesn't have the friction modifiers but the rest of their line does) next oil change. There are also people who claim that diesel motor oil works well in bikes (Harley riders especially, since I think the Harley manual recommends diesel motor oil as an alternative), but I'm not sure of brands.

Do yourself a favor and get an owners manual, and preferably a service manual, off ebay.

 

Does the Nighthawk have a wet clutch? If so, you need to be careful using automobile oil. Most standard automobile oils have friction modifiers (it will say Energy Conserving on the API logo) that make the oil slipperier and can cause the clutch to slip.

What is a "wet Clutch"?

 

The Harleys are actually built to use the diesel engine-rated oil. The "C" API rating is required. Certain oils are rated both for gas and diesel engines, such as Mobil 1 10W-40, which is about 50% cheaper than the Mobil 1 20W-50 motorcycle oil.

 

Most bikes use a wet clutch. I think the Ducati uses a dry clutch. (If I remember correctly)

 

Ducati uses both depending on the bike.

 

Don't Harleys have dry clutches?

 

Nope. The primary drive, where the engine drives the transmission via a chain, is sitting in it's own oil bath. The big silver plate you see here is the clutch access.

 

Ah, maybe its older Harleys that had dry clutches, then? I KNOW I read somewhere that they had dry clutches...