I thought the same thing when I first heard twin cam, but that is not the case. This is a question for Hippo, I think they are chain actuated and control the push rods, I think they are located on the lower part of the motor, but I could be wrong. Well any way at least you don't have to adjust them all the time. safe riding rick poco
THe fact is...all Big Twin Harley Davidson Overhead Valved engines since the knucklehead in 1939 (I think) have been built with one camshaft that had four lobes. It was gear driven by the pinion shaft from the right flywheel and controlled the operation af all four valves.
The Twin Cam is only different in that there are now two cams...one is geardriven by the pinion shaft and the second cam is chain driven from the first cam.
Several aftermarket companies are marketing gear driven twin cams for the motor because theoretically gear driven cams are more precise, from a timing point of view, due to chain stretch and slop perspectives.
That should explain the difference between the single cam vs. twin cam concept. THere are a few other differences between EVO and T-C configuation but the cam design is basically the 'real' difference. Heads, various valve train components and case and timing cover design also difer but the real difference is i the number of cams and the geometric implications on such things as pushrod angles, length and such.
Two chains. One from the pinion to the rear cam and one from the rear cam to the front cam.
Your mind is still on the FAsTBoY, but you are moving nicely in the direction of progress. LOL.
The biggest advantage of the aftermarket gear drive is that it reverses the direction of rotation of the rear cam. This allows you to run much higher lift cams as there are no lobe to lobe interference problems.
This is also the reason the gear drive requires gear specific cam sets.
If you have the pins and micrometers to measure the gears in order to match them they can be a good way to go.
The chains are fine for bolt in cams.