I have a 250 X Cat I bought new in the spring of 1969.It had a 2-1/2 HP Tecumseh,and I can tell you for sure that my guard never fully covered the sprocket and chain.If I looked straight down I could always see at least half of them.The reason I remember it so clearly is that every time I oiled the chain it would throw a ring of oil everywhere,but mostly on my leg.Almost none would hit the guard.The original clutch did not have a bolt in the crank to hold it on,but two set screws.The guard has a circle worn into the inside where the clutch hub rubbed on it,it is about 1-1/4 in diameter.If there had been a bolt there it would have worn into the center first.I just restored the bike,and put a new clutch on it.The guard now has been moved out to clear the bolt on the modern clutch.I don't know what brand the original clutch was.I do remember when the springs broke out I tried to drive wooden wedges in so I could still ride with direct drive.That didn't work so I tried clamping two pair of vise grips to the drum between the shoes.Really bad idea.Then I drilled a hole in the drum and put a bolt through to lock it all up.I would start it up with the back wheel held up off the ground by a piece of wood.I would sit on it and push it off the wood.9 times out of 10 it would take off and leave me behind.