Oring for piston in an IC engine

[Dave Perreault]

Hi everyone, I have built several IC model engines many of them Atkinson engines.
I am currently designing and building a twin Atkinson engine and concidering using an oring instead of using cast iron rings like I normally do. The bore on the cylinders is 1" diameter. I was wondering if anyone would be willing to share their experience with using orings with me.
Cylinder finish
Oring fit , compression, etc
Oring material
And also life and dependability!

Thanks in advance for the recommendations.
Regards Dave








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[Hanss]

https://www.homemodelenginemachinist.com/threads/viton-o-ring-as-piston-rings.30486/
gr.
Hans

 

[Hanss]

https://www.homemodelenginemachinist.com/threads/viton-o-ring-as-piston-rings.30486/

 

[BobsModels]

Here is a quick search for you, just do searches on o-ring, piston etc. lots of information, lots of recent lively discussion

https://www.homemodelenginemachinist.com/threads/o-ring-for-piston-ring.32327/
https://www.homemodelenginemachinist.com/threads/the-great-o-ring-discussion.32916/
https://www.homemodelenginemachinist.com/threads/turning-o-ring-to-fit-bore.32957/#post-355500
And that is just good start, there are many more threads

Bob

 

[Rocket Man]

I put Labyrinth seal grooves .020" wide, .020" deep in all my pistons they work like zero friction piston rings. I put these on all my hot air Stirling engine pistons they work better than no rings at all.

ORings have too much friction for small pistons, low power engines will not run. Stirling engines barely have enough power to run. I usually fit Stirling pistons to .0002" clearance at the run temperature.

 

[BobsModels]

ORings have too much friction for small pistons, low power engines will not run.

Rocket Man

Not necessarily so, if fitted for the application not using standard o - ring tables. This is my gade showing bounce when new, has run over 600 hours on that o-ring as of last year.



Bob

 

[Steamchick]

I learned about labyrinth seals in the 1980s, designing H-V circuit breakers. These were operated off-load annually 5 times, as otherwise the may never operate in 20 years. The compressed air driving cylinders had PTFE rings designed with zero wall pressure. The operating valves had a solenoid valve the a 2-stage high speed pneumatic power cylinder to drive the main sleeve valve. 4 msecs total operating time from trip signal to main valve fully open.
Labyrinth seals were used to avoid sticking, as the breakers didn't operate except in emergency. Some may operate 20 times in 40 years, but some never trip a fault. But they had to work when needed. There is a natural leakage with labyrinth seals so the work - gas motion and pressure dynamics. This was modelled on the company computer (limited to15 minute runs, overnight), that filled a large computer room and was not as powerful or fast as desktop computers in the mid-1990s. Valves designed in the 1960s were improved by 0.1 or 0.2 msecs total, but we're close to optimum, so not changed. Like aircraft, designs and application well scrutinised. The simple rule was depth of groove 10 to 20 times clearance, width of groove same as depth, land between grooves same as groove width. Sharp corners a must, on outer corners; a full radius = half groove width could be used to reduce stress in the piston walls, if thin. Min 6 grooves, some applications used 10 or more, but usually 6 was the norm. We were talking of some valves 3/8" - 1/2" dia, with 1/16" or smaller grooves. Materials were stainless steel and anodised aluminium. Tools looked a lot like thread chasers... for 6 grooves in 1 cut.
On my models I have ground a hacksaw blade like a narrow parting tool to cut grooves.
Hope this is of interest?
K2