People talk about doing cam upgrades. I've never seen the inside of a twin cam, but wouldn't a cam replacement in a twin cam require you to buy 2 cams? How does it work?

Camshaft controls the opening and closing of the exhaust and intake valves. If there aren't any more intake valves on a twin cam, what is the second camshaft for?

 

Really? Go find and watch a You Tube video - HOW TO CHANGE CAMS ON A HARLEY TWIN CAM ENGINE.

 

Twin cams have to two in the back of the cam plate, hence twin cam. People just call it cam replacement in general. Plenty of videos as said. 99-2006 they had spring tensioners. I went gear on this particular bike. You need a good crank to go gear. Hydraullic tensioners or new pad material is another option.

 

Each cam has 2 lobes. One cam controls valve timing for the front cylinder; intake and exhaust. The other does the same for the rear cylinder.

 

 

The rear cam is for the rear cylinder and the front cam is for the front cylinder, it's pretty much that simple. Now as to how it works? Well I could explain it but as the old saying goes "A picture is worth a thousand words", and the countless videos on YouTube are probably worth a million words.