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

Hello Tom, I have been all over the map and tryed several things...the 27 oz I temporarily added to the flywheels really slowed the engine down and I kinda liked how it ran....but I felt I was putting quite a bit of load on the engine at that weight....I am a bit concerned as there is only tiny set screws holding the flywheels on and over time they can work loose. I took All the weight off for now and am playing with compression reduction...Something to keep in mind is when I had lots of weight the engine Did run Much more slowly...But it still has to Hit quite often to keep the flywheels moving! I have had hits per min of over 55 and my current lowest count was 33 hits per min on a well lubed and warm engine..others have achieved much better than me....But I have Many more things to try!....So far the 2 single best improvements I have made are:
Remove One of the piston o-rings!...this seems to improve oiling as the space between 2 o-rings is wiped dry...this worked so well I am going to try removing BOTH o-rings!...my flame licker runs without Any rings!...this engine just seems to Want to run!....I feel 90% sure it will run without any o-rings but will report my findings yet this weekend!

The the other biggest game changer:
Find any and all parasitic drag!!!....I discovered this quite by accident...having had my Piston in and out of the engine 3-4 times...after one re assembly...I noticed my engine running MUCH more poorly...I have learned to hold the exhaust valve open and give engine a couple hand spins If I think I have flooded it...if with a stout hand flick your engine will not coast MORE than 12 revolutions...you have drag issues!! I took my Piston and rod assembly back out and the flywheels would coast more than 30 revolutions...so well in fact I could not count that fast!...so I checked piston fit to bore...smooth as butter...next checked the rod main bearing and it felt gritty!...the rod main bearing is plain yellow brass...and it is made into two "C" shape half rounds to enable assembly to the crank....I believe When made, the bearing is assembled into the rod and reamed...it is possible (and likely) to reassemble and flip one of the "C" halfs end for end....if the machine work was absolutely Perfect...this would not be an issue...but the world is not perfect and flipping half a bearing caused my rod bearing bore to not be round...I found a metric dowel pin the same size as the crankshaft journal and proceeded to try all the different combos of assembly...both with the rod end cap and the bearing C halfs, there where combos that worked better than others...but All combos produced some drag.
   The next step I took was I assembled my best combo and marked a tiny center punch mark on the rod cap to rod...I put the dots up so I can see them...next I locktite each bearing half in place...one in rod...one in rod cap, carefully centering them..when cured I reamed them .001 over with a slip fit meteric reamer...carefully re assembled everything in its proper place and my engine now coasts 20 revolutions with one stout hand flick and exhaust valve held open!!
   So far this repair is the single best thing I have done to improve my engine to date!....I don't really care for the plain yellow brass rod bearings and have big plans to change out all bearings to oil-lite bronze...when I do that I would like to pin the bearing "C" halfs in place as I don't really trust the loc-tite on a half bearing long term.
Bottom line ....I don't know if I should post all my little experiments on the forum as many of them are not helpful...or...with my assembly being wrong the first time I could not even notice a difference in the way the engine ran with lower compression!...with my bearing temp fix it does run slower than before...and....It IS super fun to share my adventures....I suppose folks can learn just as much from my mistakes as my wins...but ANY form of drag is NOT your friend when trying to get such a tiny hit and miss engine to run slow....
I guess I really did not answer your question, but something to keep in mind is: If you know you want to put your little M90 to work and power something, you may not want to lower your compression...or lower it only a little...I own 3 of these little engines and I want at least One of them to run super slow!...So I am willing to do most anything to achieve my goal and I don't care if I can stop it with my little finger...as long as it runs well and runs slow!...I will build one of my other engines for powering implements...your mileage may vary!