Yet more Minnie assistance

Due to finding that the hole for the piston (on the Minnie) was drilled (by the previous owner) is not concentric and is "straining" the piston rod I have had to scrap it. My problem was/is I did not have any gunmetal/brass to make a new one. It is at the end where the guide bars are. I have found a piece of cast iron that is not far off. Just wondered if the use of this ( maybe temporary) could have an adverse effect on the engines operation? I do not foresee a lengthy period of steaming the model when complete, more likely running it on air, but any comment would be useful!

Could you not open up and then thread the existing eccentric hole in the piston and then "let in" a piece of threaded brass or gunmetal into the enlarged tapped hole - and then drill and thread it concentric to the OD? Something like an oversize Helicoil, retained with Loctite 270.

Should not be a problem with iron, put a bit more oil through it at the end of a run. Aluminium is also a popular choice on traction engines.

When you come to make the new piston leave it a little oversise but cut the groove to finished depth. Drill counterbore and tap. Then without removing from chuck the piston rod can be held in the tailstock drill chuck and the two screwed together which helps keep things in line.

Now hold the piston rod in a collet, split bush of 4-jaw so it runs true and skim teh OD of the piston down to size which will get it as concentric as possible to the rod.

Thanks to both Nigel and Jason B for their replies, I did think of your solution Nigel, but the whole part looks quite "scruffy" so decided to start again. I did make a new piston and rod as the original piston was "rough " to say the least. I have quite a bit of alluminium rod of various diameters, but I will go with the cast iron and follow Jasons oil advice once I get it running (if I ever do as I have had the engine just under a year and made or re-worked various parts of the motion, a lot of frustration but hopefully I should now be haeding towards a finish, wheels done, tender done, brakes etc.,!!