Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines
The Regular Stuff: Chat, Buy, Sell, Off Topic, etc. => General Discussion - Scale Model Gas Engines - Hit & Miss - Throttle Governed - Non-Compression – etc => Topic started by: Hans de Bruin on January 04, 2025, 12:40:42 pm
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Bonjour Hans,
Personally, I have never dared to put any thread locker on my little engines, considering the small sizes of the different screws, nuts and bolts and their possible fragility when unscrewing.
I wish you will find this alkylate type of gasoline, it is really great, before I used to put 4 drops of 2 stoke oil in the tanks with SP98. I can see it on Amazon :
https://www.amazon.fr/s?k=essence+alkylate+2+temps&crid=31S8BUW01EW35&sprefix=essence+alkylate%2Caps%2C105&ref=nb_sb_ss_ts-doa-p_2_16
My thoughts also on the loctite.
I see 55 different brands. Which are you using ? The Stihl brand seems ok for price & shipping to Greece (10 euro / ltr) but it doesn't mention
the word Alkylate....
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Yes I did notice quality is not consistent. But then again, we get this magnificent jewel for this price that we
can actually afford. And with it comes the ability to improve on its flaws by speaking to fellow enthusiasts.
Compression has increased noticeably during run in, and with it the spray has decreased significantly. So the diagnosis was correct, but
I'll leave the head on for now. Can always do it later. Indeed I had gathered the normal lapping cream would be too rough.
My project for today is to fix the migrated pin where the cam follower bearing is on. It has moved inwards and now the exhaust pushrod
is sticky. I'm thinking getting the steel pin out of the brass part, clamp it in the vise to damage the end a bit, then drive it back
in with a bit of epoxy.
The springs, I'm on it. Scouring the house for some old equipment that might contain some....
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> It's new. Shouldn't it be lapped and ready to go?
Yes, it should be, but don't bet on it. QC varies in model engine land.
The problem could be something simple like a bit of trapped swarf or a burr. If not....
Because the valves are quite tiny, they need fine abrasives. Things I've used that work at varying levels of efficiency are toothpaste, tin oxide, and bathroom cleanser. I've had good results with SoftScrub.
Apply just a small amount, you don't want the abrasive to get onto the valve stem and into the valve guide. Check frequently, rinse and repeat until you get a clean seat.
Re: Running too fast
Use softer springs on the governor weights. With the OEM springs, using a single spring will help a bit.
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Bonjour Hans,
Personally, I have never dared to put any thread locker on my little engines, considering the small sizes of the different screws, nuts and bolts and their possible fragility when unscrewing.
I wish you will find this alkylate type of gasoline, it is really great, before I used to put 4 drops of 2 stoke oil in the tanks with SP98. I can see it on Amazon :
https://www.amazon.fr/s?k=essence+alkylate+2+temps&crid=31S8BUW01EW35&sprefix=essence+alkylate%2Caps%2C105&ref=nb_sb_ss_ts-doa-p_2_16
In all the cases, never more than 4% oil in your mixture otherwise the engine spits it out !
I have also tried "Essence F" but have not been convinced.
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Answering my own question here. The spring under the adjustment screw is too strong, making it hard to
feel the end point of the needle. I'm gonna look for a softer spring to put there.
Also I modified the 'coasting link' (what IS the name for this thing that keeps the exhaust open) so it can never
touch the cam gear again.
.... and I just noticed the little shaft that the cam follower is on has moved inwards a bit. Have to look at that
tomorrow. And find a better way to fix this in place.
Any of you using loctite ? I'm hesitant to use it. In case of difficulty when something needs to be taken apart again.
I'm trying to find this Alkylate. Not easy here in Greece it looks like....
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All is well, but yes when warmed up and after running out of fuel, it is almost impossible to get it running again. Very
sensitive, the adjustment.
Also, when setting the needle, I close it, and then turn it back let's say 1/4 turn. But sometimes the fully closed point
seems to have moved ? I made a little dot on the adjustment screw, but it is not always on the same position when I close it
fully. Not sure what's happening here.
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Bonjour Hans,
Great progress indeed, bravo !
Based on my experience with these little engines (I have made a Playlist for this topic : https://www.youtube.com/watch?v=Q91Ju0Peu2Q&list=PLCVcZL8L7sBJ-ILRmMDuBQk9Jz-aOd-AE&pp=gAQB) they are AWFULLY difficult to adjust.
I work by trial and error on only a few degrees forward or backward for every new test as the temperature of the room is never the same.
Furthermore, I noticed that sometimes the mixture air/gas has to be just a little little bit adjusted (closed) when the engine gets warm.
As gasoline, I was suggested Alkylate 2T and it is great advice :
https://www.google.com/search?client=firefox-b-d&q=essence+alkylate+2+temps
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It's still a far way off, lots of tweaking required. But first I'll just run it a bit, get everything seated a bit, and just enjoying
the sounds and smells of it.
Also now I think of it, I'm running it on the same fuel I use for the Cison V-Twin, which required 1:25 oil content. Might be too
much oil for this engine. Using Zippo. Difficult to get Coleman fuel here in Greece....
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I'd say it was likely a combination of both improved timing and run time seating the intake valve better!
In any case, congratulations on your efforts to make it run better!
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Have to say, the spray coming from the inlet is a lot less. After running it a bit it's hardly noticeable.
Maybe the ignition timing did the trick ? Maybe the inlet valve seated itself better after some run time ?
Still a bit of a mystery to me, these little engines.
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And after a while it just sputters and dies.
Is there an easy way to see if you're running too rich or too lean ? I'm around one quarter turn open, but it has difficulty
staying running for any length of time.
Any tips and tricks highly appreciated. I'm learning. And loving it !!
https://youtube.com/shorts/XvZK0BA0nJY
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It looks like my exhaust valve disable thingy is too far away ? It's not coasting very long, and it runs rough. It starts easy though.
https://youtube.com/shorts/8ObmvDs1o-8
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Welp. Got it running again. Lots of nervous time getting the flywheel off. But in the end I was victorious. Damage to shaft
and wheel was limited to some burrs. Easily sandpapered away.
Next I drilled the shaft where the setscrews are, so the flywheel will stay in place this time.
I reassembled everything, adjusted spark timing to TDC (it was a little before TDC) and test ran it.
The adjustment of the spark seems to have improved the spray problem. But it's still there. Hope it shows on this video.
Spitting time !!
https://youtube.com/shorts/ixsTS28FPq8
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Bonjour Hans,
To prevent the steering wheel from moving, we made a flat on the crankshaft axis on which the clamping screw rests.
And I have to go to my workshop to take the measures you wish, in my opinion, the point is that your crankshaft should not be able to move laterally.
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Removing the stuck flywheel. I'm now in the "I'm done asking nicely" phase....
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Removing the stuck flywheel. I'm now in the "I'm done asking nicely" phase....
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It's new. Shouldn't it be lapped and ready to go ? Anyway I'll try to fix something to put air pressure in the cylinder and see where it leaks. What do you use on these small engines for lapping ?
Before I take the head off I might try adjusting ignition first, that's easier. Right now it sparks a bit before TDC.
But before all that, I have to fix the flywheels. Apparently it moved inward, allowing the lever thingy to hit the cam gear. The flywheel is free and rotating, but doesn't want to come off no matter how I pull it. Both set screws are backed out all the way and the collar on the back is loose. Still it won't budge.
Also the flywheel on the other side is loose. I tightened that. Raphael in the video you mention you fixed this issue. How did you do it ? I imagine every time the engine hits those poor setscrews get a lot of force to resist...
And what would help me greatly is for someone to measure the flywheel on the cam side, how much is the crankshaft inside the flywheel. It's almost flush now and it sure wasn't like that.
See pic.
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.... spray coming from the inlet ('carburettor') during the hits....
It could be combustion pressure leaking past the closed intake valve and blowing out through the carburetor. The fix would be to lap the intake valve.
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Bonjour Hans,
Sorry, about the inlet valve, I wished saying that there is no "direct" link between it and the carburetor, the gas does not come from this valve, it just opens while the piston sucks gas so can't push gas through the carburetor.
About the timings, yours seems bizarre for me because mine seems sparkling at top dead center, a bad timing could possibly explain an exhaust valve opened during the compression phase letting a part of the mixture fly through the carburetor.
And about the lever, It was possibly too loose, just after top dead center, mine has a little play of less than 0,5 mm
I also would kindly contact this guy from me, https://www.youtube.com/@ThomasPCGuruENGINES , he is a great mechanic of these engines and likes sharing with us. Bad luck to meet him, he lives in Australia !
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Forgot to mention. I checked timing on the exhaust valve. It starts opening about 45 degrees before BDC, and is completely closed just after TDC.
Ignition timing is a little before TDC.
I have no idea about timing for these little hit & miss engines. I'm a complete noob.
Hans
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Ehr what do you mean "And there is no link between the inlet valve and the carburetor"
Isn't air/fuel from the carburettor sucked in through the inlet valve ?
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That's a great video ! I'm going to get mine running like that too.
Update: The spray as I described it must be a fuel/air mix being pushed out the carburettor by possibly a leaking inlet valve. But compression feels good. So I'm not sure there. It also starts by hand when warm, and runs great.
But things just got worse. In previous runs today I did hear a weird sound from time to time. When I went to run it just now to make a video of the spray I found out what it was. It was the lever that keeps the exhaust valve open hitting the gear. And just as I was running it now it hit it hard and the lever rotated out of the way letting the engine rev up max. Scary. Stopped it immediately, and I'll have to figure out what caused that. So I have two issues now. I have the idea the flywheel moved and this caused the issue. Don't know, I'll investigate tomorrow and try to upload a video.
Thanks so far,
Hans
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Bonjour Hans,
Among others I have the M91 and also had to solve several issues.
My question is : What do you mean when you write "What I can't seem to solve is spray coming from the inlet ('carburetor') during the hits." ? Sorry, my English is not my native langage ;)
What could this spray made of because for me a spray is the vaporization of a liquid ? And there is no link between the inlet valve and the carburetor
To my opinion, if you had a leaking outlet valve, your engine would not run and you should feel almost no pressure when you turn it by hand ? => Do you feel a pressure ?
Other test I would kindly suggest you to close the carburetor with your finger and turn the engine in its direction of travel, you should feel a suction => Do you feel it ?
Do you see the spark at top dead center ? This confirms it starts on the correct timing side
And if you could make a little video of your issue, it would greatly help us to analyze it ;)
https://youtu.be/BVW-0gibXKM
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First, let me offer you a very big and warm WELCOME to the Forum!
A video would no doubt help in identifying the issue, but a leaking intake valve, which could be caused by a timing problem, seems a likely culprit to me!!!
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Good afternoon !
Just joined this forum, because I bought my first hit & miss engine and I'm reading up on them.
I bought an Eachine ETX / M91 vertical hit & miss. A thing of beauty. It arrived damaged (cam follower bearing broken during transport).
They are sending me a new bearing but in the mean time I managed to install a locally acquired bearing.
Now my question. Engine runs great. When it is hot it even hand starts. As I read here I'm experimenting a bit with different springs.
So far so good. But....
What I can't seem to solve is spray coming from the inlet ('carburettor') during the hits. I don't see that happening in any of
the 1000 videos I watched on youtube. And I can't explain how this could happen. Leaking inlet valve ? Valve timing ?
I'm at a loss.
Help.
:)
Greetings from Greece.
Hans