Hi laman - I don't honestly know. It is pretty dry in my part of FL now. The fire dept guys told me that mower fires do tend to happen around here starting this time of year through Jan (they "dry" season in FL). I don't know all that much about how flammable the hydro fluid is (20w50 oil). If some fluid ignited I'd think it had to be gas. There is a hole in the front of the aluminum block on the engine big enough to stick your fist through. It was from the front of the engine that I first saw the flames, but it could have been coming up from under the engine. I had mowed through a "woody" area. It is possible that a stick or small branch got run over and wedged near a pulley or belt and perhaps some friction caused it. Again, I honestly do not know.
On a separate note, I have hooked up with a guy that has a small landscaping business. He has a Tiger Cub that was involved in a highway accident while it was on his trailer. His insurance company paid for the trailer but did not cover what was on it. The SCAG ended up being hit by a truck and the frame is bent. His Cub only has about 800 hours on it. He is actually interested in my frame! Only thing I don't like about his Cub is that it has a Kawi and mine had a Kholer. He has since brought a 61 inch SCAG that he uses now. He said though that he has some small fenced properties that were perfect for his Cub. He has laughed at some low-ball offers of $300. He said he would sell it to me for $1000 or possibly buy my frame. He is sending me some pictures. We'll see where this goes.