We show you how to change primary fluid on a 2003 Harley-Davidson Dyna in easy-to-follow steps, from oil drain to refill, from tips on checking fluid levels to tools to do the job. We used MOTUL primary oil for this job and the process will be similar on most Twin Cam Dyna models, but check your manual for specifics. Be sure to change your primary oil about every 5,000 miles.


2003 Harley-Davidson Dyna


T-40 Torx

3/8-inch ratchet

T-27 Torx

1/4-inch ratchet

Torque Wrench


1.       Drain fluid by removing drain plug on bottom of primary using a T-40 Torx socket.

2.       Check top of primary plug for metal shavings. It’s magnetic so any metal scrapings or shards will stick to it. A little fibrous material from your clutch is normal, but if there are any big metal chunks, you’re going to need to have your primary inspected.

3.       Using a T-27 Torx, remove derby cover (5 bolts) and derby gasket.

4.       After the old oil has completely drained, put the drain plug back in. We suggest wrapping a little Teflon tape around the threads to help prevent leaks.

5.       Refill primary with 26 ounces of Motul primary oil (for a 2003 Dyna. Check your manual). If you don’t have a way to measure, just fill it up to the bottom of the derby cover with the motorcycle straight up and down. We suggest using a Fast Funnel. They’re cheap, disposable, and can be easily stuffed in a pocket or toolbox.

Don't skimp out on buying a new derby gasket. 

6.       When you pick up your primary oil, make sure to pick up a new derby gasket as well. It’s cheap insurance, and if you don’t, most likely it’s going to leak.

7.       Replace primary gasket and derby cover.

8.       Tighten bolts down in a star pattern (see video at 3:09) to 100 inch-pounds. (Max is 108 inch-pounds).