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

What a jewel. It is my first hit & miss model engine, and I'm loving it. But I would like to share some of my experiences here, so a future Googler might be helped in some way like I was by the articles on this forum and the help from its users.

So. It arrived damaged. It had been shipped upside down in the cardboard box, and the foam on the bottom was not enough to take the hits on the exhaust valve rocker arm. The cam follower bearing was in pieces, the pushrod slightly bent, and somehow the crankshaft was also bent. The flywheel on the side of the camshaft had quite a bit of runout. Not sure if the latter had anything to do with shipping.

Anyway, right from the start I had to take the whole engine apart, straighten the crankshaft, straighten the pushrod and install a locally acquired cam follower bearing.

After this was done I could finally run it. But it didn't run for long. The two flywheels are mounted on the crankshaft with two set screws, and this is not enough to withstand the hits after the misses. They had come loose, and burred the crankshaft, making it a struggle to get them off. I manufactured a makeshift puller and after some hard work they came off without too much damage. Not without some stress because quite some force was needed, fearing breaking the flywheel itself.

I drilled holes and flat sides where the setscrews attach, so the flywheel can't rotate even if the set screw comes loose a bit.

The ignition timing was set to about 10 degrees before TDC. This is too early, so I adjusted that to fire exactly at TDC.

After this, it was running again, but not for long. At the second run the governor lever that keeps the exhaust valve open during the misses managed to hit the cam gear, and eventually rotated away, receiving damage from the gear and causing the engine to run away. The solution here was grinding away some material on this lever so it could never hit the cam gear again even when fully actuated.

Also I noticed quite some axial play in the crankshaft. Apparently the main bearings came out of the crankcase a bit. The solution for me was (again) complete disassembly, and adding some washers between the crankshaft counterweights and the crankcase, keeping the shaft centred. If you have a lathe (which I will have soon) a good suggestion (hey Raphael) is to make a shouldered bush instead of the roller bearing. This would get rid of the axial as well as the radial play that the original bearings have.

After putting everything back together again, and some good run time, the exhaust valve became stuck open. After some investigation it turned out the cam follower bearing pin had migrated toward the cylinder, and scraped against the housing. I removed the mechanism, removed the pin and deliberately damaged the end a bit in the vice. The pushed it back into the pushrod connection with some superglue. It has stayed in place ever since.

And then the last thing I did was valve lapping. Twice. From the beginning this engine was spitting fuel from the carburettor. Finally, I bit the bullet and did this. It did improve compression I think. And the spitting is now almost nothing. But still I feel there is some leakage. When I close the carburettor with a finger and rotate the flywheel, at some point it pushes the fuel in the hose back into the tank. This implies still some valve leakage, but I'm not sure if these small valves and light springs ever can provide a 100% seal. Anyone else have fuel being pushed back into the tank ?

Anyway. Wall of text. Bottom line is that this engine is amazing. But out of the box it is not a finished product. It needs some improvements like the ones I described. But it is totally worth it ! Also it is very much fun to tinker with it. And let's be honest. For this money, even with the need to put some work into it, you are rewarded with a shiny little engine that purrs along when it's running.

Mine is almost there. I'm expecting some improvements when I get the lighter flyweight springs, and the better fuel (I'm now running on Zippo fuel with 1:25 ratio oil, which is probably way too much)

Below the result. Apologies for the verticality of the footage. I hate 'shorts' myself. But I noticed my mistake during upload.

Greetings,

Hans

https://youtube.com/shorts/0xFu_t93KH0

Hans the more I read about these the more they seem like 'kit' engines.
Everyone (including myself) seems to have to do a lot of mods and upgrades to them.

Bonjour Hans,

I fully agree with you, these little engines à quite funny but would deserve much more attention from the manufacturer,

I always have issues with my new engines, more or less serious, and my M91 did not escape this curse (loose flywheels,...)