Piston ring failure

[Parksy]

Hi all

Something that has intrigued me is when people say they haven't had any luck making cast iron piston rings. I have done the research and am aware of the different methods everyone employs when making them.
My last engine employs piston rings and works nicely with good compression, at least I think it does. But when making the rings, I didn't use any precise methods for setting the ring gap and only annealed it with a propane torch without removing oxygen sources.
So I guess my question is, what constitutes a ring failure?

Thanks all

Andy

 

[gbritnell]

Hi Andy,
As the word implies failure would be a failure to do the intended job. In the case of a piston ring that would be wearing out or breaking, and I've never heard much of the latter.
For the home machinist the most common material for rings is cast iron. I use a material named Durabar (trade name) or Schedule 40, both being ductile irons. I have made them by the Trimble method and a few times like you describe. The most important thing is that they are made to fit the intended bore otherwise there is a loss of seal and therefore compression. There are different schools on end gap clearance but usually I try for no more than .002 on a 1.00 inch dia. bore. (.05 mm on a 25 mm bore) As the rings seat in that gap will increase slightly.
As far as people saying they don't have any luck making them I think it's a matter of not wanting to spend the time to make the necessary fixtures or the multiples required for a multi-cylindered engine. In most cases it's just easier to use an O ring and when it wears out replace it.
gbritnell