At those prices i would call them damned expensie not simple some suppliers just dont know how much to charge still if your a cheque book model engineer you might be foolish enough to pay these rob dogs and keep them in their mansions
I thought I would try shallow grooves that should pick up the steam oil and possibly provide an adequate seal. If that fails I might try graphited yarn or ask for advice from our learned forum members. Just out of interest I try to use metric threads where possible as I'm not building miniature replicas but when it comes to things like boiler fittings I use the Model Engineer threads so I can buy off the shelf if need be.
Hmmm, I'm not sure what constitutes a 'good fit' for pistons on these little engines; all I can say is that the piston I've just made is a better fit than the first engine I built from a kit where the piston/cylinder was pre-machined so it should run ok on steam at least
I like the 'oil groove' idea, I'll try that next time!
Paul, I don't often come this part of the forum but I have used without any problem a flat spring for my oscilator. This is nothing more than a strip of phosphor bronze with a hole in the middle. Looks like this: _/ \_ (I cannot put a line at the top). It isn't more than 2mm high. Lenght about 30mm, 0.3mm thick. Had to do this because otherwise I needed a blind bus inside the boiler for the helical spring. Works just as well. By bending the "legs" you can adjust the force.