O rings as piston rings

[neil_1821]

I have seen this used quite a bit, especially on steam models, but I’ve been struggling to get my hoglet started and a friend diagnosed it as being down on compression, believed the pistons were perhaps too small and the O rings weren’t sealing properly. Question is, how tight a fit should they be on the cylinders? I figure too much and the ring will bind causing it to tear and too little it doesn’t give a good enough seal.

 

[compressor man]

Hi Neil,

I asked something of this nature some time ago, perhaps this would help you.
http://www.homemodelenginemachinist.com/showthread.php?t=27084

Chris

 

[neil_1821]

Ah that’s excellent info, thanks for the link! Judging from some responses I don’t have anywhere near enough compression on my hoglet. I’ll be re-machining some new pistons!

 

[TonyM]

I have never used o rings in an ICE but if I did I wouldn't use anything less than viton.

 

[el gringo]

I have never used o rings in an ICE but if I did I wouldn't use anything less than viton.

"I have never used o rings in an ICE but if I did I wouldn't use anything less than viton."
I can make the same statement with the caveat that of several ic engines (mor'n a dozen) I used viton o' rings on three 'Henry Ford first Engine'. I don't run them all that much but when I do they run very well. I used the standard fit tables.
http://www.applerubber.com/oring-gland-calculator/

Ray M

 

[neil_1821]

Cheers Ray, that will be very handy when I get the hoglet back! Need to go scrounge some aluminium now

 

[bobsymack]

Why not put a light shim under the o ring to tighten it up , save you making a new piston.
Vince

 

[neil_1821]

I had thought about shimming it out, but I want to measure the pistons again just to check they’re not undersized. I think it may also depend on how much they’d need shimming but it’s worth experimenting with.