Why were the early revolvers not converted to rifles?

They had them. Colt had several models that were all based on an 1836 model which was adopted from an 1813 model. (I know nothing about the 1813 model, I just saw the reference in an e-gun shop section on "cylinder rifles")

The Henry rifle actually descends from a design of 1842, and the first versions of the "Volcanic Repeating Rifle" were being manufactured by 1848. The Henry rifle was developed in the late 1850s, and it went into mass production in 1860. Federal soldiers who used them were obliged to purchase the weapon themselves, and supply their own ammunition--but they were willing to do so if they had the funds and the opportunity, in the belief that it would save their lives. I believe that it is correct to say that no units were equipped (officially) with the weapon, although many accounts of the battle of Shiloh report that the Seventh Illinois Regiment of United States Volunteer Infantry was equipped with Henry rifles.

The Winchester repeating rifle did not soon replace the Henry. The first Winchester model based on the Henry did not come out until 1866, when the Henry was no longer being produced. The Winchesters did not take off until the Winchester '73, which was a center-fire rifle, and therefore, more reliable than either the Henry, or the earlier models of Winchester. Basically, the Winchester repeating rifle did not come out until almost 25 years after the weapon had been invented.

It looks like the early revolvers used cap and ball

http://www.colt.com/mil/history.asp
It looks like the Colt revolver didn't use brass cartridges until 1855 when they bought the patent from Rollin White and had a factory that could produce 5000 a year.
http://inventors.about.com/od/cstartinventions/a/colt_revolver.htm

The Henry rifle was introduced in 1860.

It is also my understnding that the first repeating handguns from time to time would chain fire rounds in the cylinder a very bad thing for a handgun and far worst thing for a rifle and the larger the round the more likely it would be to have chain fires occuring.

AS I SAID BEFORE.THEY DID MAKE CYLINDER RIFLES> THEY WERE SIMPLE TO LOAD CAP AND BALL. Totally different mechanism than a normal "trapdoor" breech rifle which preceeded tube type recievers(These needed the brass cartridges).

As farmerman has already mentioned, cylinder-fed long guns were available before the Henry or the Winchester. They just never caught on for whatever reason. Accuracy may have had something to do with it. We may laught today at those cumbersome Sharps and other muzzle-loaders, but in the hands of an experienced marksman those one-shot wonders were absolutely deadly even at 200 and 300 yards. But it's a trade-off. The M-16, currently being issued to the US armed forces, isn't nearly as accurate as the old World War II Garand M1. And that wasn't quite up to the standards of the Springfield 30-'03, which is what the Doughboys carried in the Great War. But the Springfield was bolt-action whereas the M1 was semi-automatic and the M16 has a fully automatic option. As I said, it's a trade-off.