Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Hello Tom, I did read your piston port post. Gil made a post about the stock o-rings...they are green and more soft and stretchy than any I have encountered in my trade...he suggested they are stretched on the piston and the grooves are machined deep enough that they do not touch the bore at all during coast!... They are so soft he suggested they swell out to the bore under the pressure from a Hit...then relax to a zero or near zero drag...I can not confirmed or deny this, but Gil is very experienced, and I see no reason to doubt him...what I Can confirm is my stock teflon o-rings where a fail...for now...they are rigid and stretching them over the piston deformed them badly...my next experiment was to cut them with a scalpel so I could open them like a metal piston ring and fit them in the groove...this method looked awesome as they fit the groove so well you could not find the split... However..they DID sit very slightly proud of the piston and when fit into the bore they did go in...but very tight! I suspect if I machined the grooves a bit deeper AND took a tiny slice out of the ring gap so the o-ring O.D. could get a little smaller...the engine may run on them..your piston port post would certainly take this to the next level.

When I saw my teflon rings where Not going to work without extensive Mods I put one green o-ring back in and layed a machinist square along the piston to see if I could confirm Gil's post that they do Not touch...I could not tell as my eye sight has gotten to where I need readers...BUT....I Could tell the green o-rings do not hold my square away from the piston! It was 100% touching...when I get in there to remove All o-rings I will check more carefully with my best readers to see if the green o-ring even touches the straight edge...If it does Not touch...But is so stretchy that it does jump out and touch on a Hit stroke, that is brilliant!...I am Not saying we can not beat it as a ring that soft is quite "grippy" or possibly "draggy" on the power stroke...but maybe we don't care IF it makes more power!

I am not ready to take Any mod off the table yet including piston porting...It just makes me all the more eager to try to run the engine with zero o-rings and measure the green rings more carefully and also see if when sliding a well lubed piston into the bore if I can even FEEL when the rings enter the bore...this will tell me a lot about if they Are touching or not.
A word of caution: the rings are so soft it is easy to put "Twist" into them if you just stretch them over the piston then roll them down till they snap into there grooves...next time I experiment I am going to take more care not to introduce any twist...I hope anyone else with knowledge of these interesting little engines will keep sharing please!