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

I have found the same as you...the less MM oil in my Zippo fuel, the stronger my "Hits" are....I have never gone as low as 1 drop per fuel tank...my lowest was 3 to 4 drops,...BUT....I feel 1 drop may be just fine. I want to add a functional drip oiler to the piston/skirt/bore first...then drop my fuel mixture to less oil content...every time I pull my head there is quite a bit of MM oil in the combustion chamber...as others have stated it does not seem to burn up so it seems to hang around for quite some time....AND reliable Strong Hits are very desirable when tuning for slow run.

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!

Hey Jack,.. the M90's H&M coasting low firing duty cycle % resulting very Low operating temperature puts it's compression & combustion gas sealing stresses more similar to pneumatic cylinder environment conditions & with light oil lubed cylinder, the Fluorine O-ring's < 0.1 sliding friction Coefficient # is probably significantly Lower than the best all metallic piston ring package & again, 90% of H & Miss physics is Non-pressure gas sealing, Coasting condition & the much Desired Higher Miss cycle counts between Hits running appearance & sound...The In-line 4 is a totally different, Non-coasting, constant hit, higher temp,  cylinder combustion sealing emphasis expectation condition..It would Seem a premium grade Pneumatic cylinder piston, Ring & Cylinder wall Finish construction model would be the optimum overall running design, assuming using a properly dynamicly functioning flourine O-ring...The factory stock M90 piston ring Groove & Cylinder wall finish machining is probably Not optimum & worth optimization tweaking. For example, the M90 cylinder bore finish seems irregularly Random & Not optimized, uniformed Ra cross-hatched finished for typical sliding flourine O-ring performance...But..your Metallic ring perfomance up-grade issue...that's a Perfect, M90 real world performance comparison Experiment !! ... I'm not equipped, but I encourage anyone interested to do it ! Thx for your interest & response, ...tom.

Yes. The two ring set up seems to cause premature ring failure, as not enough oil passes between them. I’d think removing the bottom ring would be fine.

Man,...that 32cc inline is a Sweet looking mill !!  Pricey, but compared to the M90's cost... it's a $teal with all the functional detail, liquid pumps, absolutely Beautiful Radiator & that really cool ignition Distributer !!  I'm sure the metallic  piston Ring upgrade will improve issues but u might check out the cyl bores for correct Crosshatch Hone Finish to achieve optimum ring break-in....I would hit the "Buy" button, but I'm in middle of full scale muscle car engine build & Need to keep budget & time focused on getting the 426H project runnin......tom.

I've noticed lately, hard stainless steel slick finished liners being used with rubber O-rings as that combo doesn't go thru a break-in....I would think metallic piston Rings would break-in better with traditional cross-hatch honed, iron cyl Liners...Once you get 'er runnin steady & clean, maybe fab up some tuned exhaust headers & a tuned Ram intake manifold !!  That motor got a tach yet ? ......tom.