225E valve gear problem

Perhaps put a dab of Loctite (blue or purple, definitely not red!) on the threads of the screw holding the eccentric crank.  Don't run it until the Loctite dries, hopefully it'll stay in place.  If not, your screw is too short, or the threads in the wheel are stripped (which is a harder problem to solve!)

On the other hand, if the problem is that the "nubs" on the eccentric crank are worn, you can get a new crank.  If the holes where those nubs fit into the wheel are worn, you would have to replace the wheel, which on a 225E is more of an expert-level repair.  My $.02.

Some of the early steamers have a half moon keyed eccentric crank.  I have both typs and the rivets to attach the eccentric rod.