[Healeys] 100-6 misfire and low oil pressure

[philritten at aol.com]

I recently purchased a 58 100-6. It runs wonderfully on cool days, however recently we had a 105 degree day and I noticed that the usually smooth sound coming from the tail pipes had a "puff" sound in it on occasion. However, the next morning it ran fine and has since. Today, I took it on a short drive on the freeway and pushed it a bit. When I got home the "puffing" noise was back and the oil pressure had dropped to 20 from the normal 50. Any thoughts? Could it be rings?

Thanks