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!

Hello Tom!....I am glad a few folks are following along in my adventures with tiny hit and miss engines,....I Will continue to post both my Wins AND my losses....as we Can learn from when things get Worse as well.
     I have not removed the second o-ring yet as I have obligations today....but got the idea from a forum post of the full size engines...they where talking about slowing down full size hit and miss engines and retarding the timing often came up...but one guy said he likes to find an engine that is " loose" with well worn piston and bore and noticeable blow by of the rings...this is a lower drag engine and the ring blow by also has the effect of lowering the compression ratio of an all ready low C/R engine!.... The piston to bore fit (on china engine) is fairly close in my opinion for a hit and miss engine....I am hopeful that Just the film strength of MM oil will give me enough seal to run.....I suppose a thicker oil would greatly improve seal but that would not help with the low drag...I don't know if there is anything out there as thin as MM oil that has lower drag characteristic.
   Speaking of oils...I did read your thread about getting down to 38 hits with just fancy oils and a softer Gov. Spring....Gil posted an answer to one of my questions about which model china engine might be the best to tune for slow run and he suggested the M90 model you have....I have one new in box and think I want to get it out!....I saw a video last night of an M90 with head removed and it "looks" like the M90 has larger valves than my M94....I want to measure to confirm this but the combo of larger valves PLUS M90 has valves in the head so the air pathway is the best and shortest pathway possible.
   My M94 the exhaust has to travel up the threaded spark plug hole...then turn 90 deg and go down a long smaller hole then thru a brass side exhaust feature....I think the M90 is a better place to start for performance tuning....glad I just happen to have one in stock....lol
    As long as we are brain storming....I had another idea....one of the best upgrades you can do to a flame licker engine is make the entire ring-less piston from graphite!... This allows you a self lubricating Very low drag piston....key to making this work is a very well polished bore as the tipical cross hatch scratch pattern will slowly wear away the piston....if the bore Starts out polished and the piston starts out close fit...it Can be a long life piston......I do not know if Solid graphite piston has ever been tried on an internal combustion engine as the forces applyed to piston are much greater than any vacuum engine....however....our little hit and miss run so cool that o- rings live for a long time...and if we lower compression significantly...they run cooler still and with less strain.....I have access to some super hard premium graphite used in the tool and die trade....I want to Try it some day in the future......specialy IF my engine runs well with zero o-rings....thats all I have for now...got to go fill obligations.....

Hey !!!  Just got  33 Hit a min  ......Gettin there !!

Sadly my employer has kept me so busy there has not been time or energy to work on my little engine...hopeful that will correct soon!.... I did stumble on a modified M90 video and thought I would share with those interested in tuning these sweet little engines...I think he made a different power supply...BUT... Also installed a drip oiler..he bent up some copper tube to run external to lube the piston skirt....I would have drilled the top hole thru bore liner and dripped the skirt from top only...but it is fun to see how other Craftsmen solve lubrication....he has it slowed down pretty good, though not to Gil's engine level of tune I think...thought I would share link.

Great work guys....!!!

Please continue to update us.

Gil

Hi Ben,...a Tach IS nice but Not required for our H & M  Common interest Improvement measured progress purposes...Your Existing cell phone device using Digital Stopwatch mode & Counting Hits per min + Video Camera Record mode at 1/4 or 1/8 Slo-mo speed & counting Audible "Huffs"(coasting strokes) between Hits does same + let's you Observe subtle Dynamic nuances (intake valve action, governor weights & Latch-out action, etc actions...The instruction sheet specing 95# (octane) fuel is a clue of near 10:1 CR way too high for realistic H & M Rpm as I don't plan to drive any accessories...4.5 CR is probably near optimum power hit to Flywheel inertia pump over & that's gonna require a good size piston top cut...I plan to fit the piston skirt with some small Teflon clearance "Buttons" which combined with the upper O-ring, should Totally remove all piston to liner Metallic physical contact friction & sliding scuffing.....tom

Note on octane:  several years ago I was moderator of a group of scooter enthusiasts. The engines our scooters employed were ordinary OHC four stroke made in Taiwan. The manufacturer spec’d them for 95 octane. I did some research and reached out to the representatives in Taiwan about this, as many of our US owners were concerned.

Turns out, there are more than one way octane is measured.  Bog standard 87-89 octane US gasoline is exactly the same as the 95 octane Asian measurement. It’s just measured using a different scheme. 

Ordinary pump gas is all you need, and it’s likely the nominal compression of our little engines is more along the lines of 8 or 8.5 to 1.   That would be assuming a running engine with ideal dynamic ring sealing. Hand cranked testing would likely be lower. 

Note on tachometers. The inexpensive laser optical handheld tachs available for twenty bucks or less work great. 

Bog standard, a slang I picked up from my English motorcycling friends, refers simply to ordinary pump gas, or may refer to the very common, dirt cheap 15W40 motor oil often sold in bulk for Diesel engines. The Brits I knew were all about saving a penny when they could.  If I had to guess, the reference might be from back in the day, when cheap coal, only a step up from peat might have been so named. It would be synonymous with “garden variety”.