Did I Wreck two piston rings ?

[David Powell]

I am trying to improve the performance of our 4inch scale Clayton undertype steam wagon. It has two cylinders. The pistons each have two rings, 1/8 th inch wide. One cylinder is bored about 30 thous oversize and with the rings fitted the piston can be moved with reasonable thumb pressure
Now to the other, it is bored virtually dead on to 2inch diameter, With the rings as fitted by the original builder the piston needed a 20 odd pound push to move it,
I remembered an old motorbike mechanic showing me a trick to reduce friction, he took the ring tightened it in a hose clamp, heated the lot to red and let it cool slowly, On releasing the clamp the ring then had much less spring.
I tried it with two rings, they lost most,.but not all of their springiness and on reassembly, the piston can be moved with just a light push.
Do you reckon the modified rings will work allright?
Regards David Powell

[macona]

Sure. You just relieved the stress in them so that took a shape closer to circular. Aiming cast iron rings you probably did not change the structure of the cast iron much.

[nickel-city-fab]

The only real answer will come from a vacuum gauge, I think. I doubt you are running condensing, but you can see how much vacuum a cylinder draws, and how long it holds it. I think you will want some tension on those rings. Maybe not 20 lbs worth, but still some.
The good news is that you can probably put some tension back in them, the same way you took it out. I've done that before at my old job --

[I make chips]

Yes, you 'resized' it with your heating process. You can try the below procedure but if it was mine I'd buy new rings.

Many rings are made with the exactly opposite process. Perhaps 100-200 of them are placed over a larger mandrel to expand them then are heated 'red'. When cooled the ID is now larger and you have the right amount of spring tension for the ring vs the bore diameter. I sold a precisely controlled heating system to a major manufacturer for this application and it worked slick.

[A.K. Boomer]

If it's just steam and easy to see the blow-bye why don't you just try it and see as long as it's not a nightmare to disassemble ?


If it matches the other side then leave it be.... you don't need much for steam in comparison to an IC engine the pressures are just a fraction...

[David Powell]

The assembly and dissembly of the cylinder end of the engine itself is not difficult. However, removing and replacing the 200 odd pound complete lump of an engine into the chassis of the truck is a real bear of a job, theres pipework, brake linkages and steering linkages to be worked around. Compressed air bench tests uncover the worst problems but there is no substitute for a road test. regards David Powell

[A.K. Boomer]

Wonder if they ever do "leakdown tests" on steam engines? put in compressed air and measure the amount getting by - compare it to the other cylinder, might be worth it esp if those rings you changed are already broken in and you just relaxed them some...

[David Powell]

MY usual test is to prevent the engine from turning and apply steam. A really good engine will not pass any steam by. Most show a slight blow which when running is undetectable. the amount of leakage permissible without worry depends on the size of the engine Regards David Powell.

[A.K. Boomer]

Makes sense - probably an even more accurate way would be to do the same with an air compressor that just pumped up to maximum pressure and kicked off, apply air and time it till the compressor kicks on again, do the same to the other cylinder...

[Tobias-B]

Pressure drop across a calibrated orifice is also pretty darned accurate, a la an internal combustion 'leakdown' tester.

Also, flow meters work great for this sort of thing, if you have the right range...

t