Diesel Motorbike

[SimpleSimon]

Well, a good machinist could high chrome steel sleeve an existing 79cc jug, machine a silicon/aluminum billet head, and fit an injector pump for indirect injection through the valve train. You are talking some serious work to do so.

My cousin builds small steam engines as his hobby - he has an 8 hp one in his sideyard running during the day off the steam output of a multi-plate solar tracking reflector array heating a recirculating boiler. I talked with him about building a 50cc diesel engine at one time, and after investigating the idea he decided it wasn't something he wanted to tackle - not even converting an existing engine.

 

[nadroj]

Have you looked closely at the engine cradle? I wouldn't sit on that bike let alone drive it. It appears that the builder used black pipe and plumbing fittings to create the lower frame. Not to mention the questionable welding on the attachment points.
I'm not trying to be sarcastic, but that bike does not appear to be safe.

LOL i just looked at that frame and that is outright dangerous, i love the pipe fittings for welds

 

[Flapdoodle]

In the mid 50's a neighbor kid had a German made diesel model airplane engine. Where the glow plug would be there was an L shaped screw adjustment that I *think* was to change compression ratio. Other than that it looked like any other model airplane engine except it was rather large.

If I remember, it ran on straight castor oil. After a lot of fiddling with the L adjustment, and squirting an occasional shot of what I think was regular model aircraft fuel, it finally started.

It was surprisingly quiet. The hard to start part left me unimpressed.

 

[jared8783]

Hey Flapdoodle

Whats the engine size, HP, torque, ect.

 

[Flapdoodle]

Hey Flapdoodle

Whats the engine size, HP, torque, ect.

No idea. I was a child at the time, and I never saw another one.
A search on Google gave me the impression they are collectors items now, but I did find a few that are make now. Here is one.
http://www.modelflight.com.au/enya_engines/enya_ss25bbds.htm

This is an interesting read for a conversion kit...
http://www.mecoa.com/acc/diesel/09die.htm

Note that they appear to be a regular carbureted engine, but with much higher compression ratio.

It is unlikely a Happy Times could withstand the forces involved for very long.

 

[velosolex]

Model airplane engines run on nitro methane/bean oil. They are designed to turn a prop.....fast. Our engines run on gas/oil and have to work all over their rpm spectrum. I don't think a retro fit (gas to diesel) will work. Also, the Lohmann ran on kerosene, not diesel. Kerosene is expensive and hard to find, but I guess jet fuel would be a substitute. You really need a pump and injector, plus the timing needs to be variable, and maybe even double pulsed to reduce detonation, which kills engines.

Cris

 

[arceeguy]

In the mid 50's a neighbor kid had a German made diesel model airplane engine. Where the glow plug would be there was an L shaped screw adjustment that I *think* was to change compression ratio. Other than that it looked like any other model airplane engine except it was rather large.

If I remember, it ran on straight castor oil. After a lot of fiddling with the L adjustment, and squirting an occasional shot of what I think was regular model aircraft fuel, it finally started.

It was surprisingly quiet. The hard to start part left me unimpressed.

Model engine diesels do not run on what we know as "diesel" fuel.
It is a mix of kerosene, ether, and oil. They ignite by compression, but lack the direct injection of fuel into the combustion chamber. So ignition timing is controlled by adjusting compression, not by injection timing. Starting them is pretty tricky too, as you need to increase compression to get them going, but reduce it when running.

 

[Flapdoodle]

Thanks. Now after all these years I know what that odd adjustment on top of the cylinder was for.

 

[EsQueue]

Has anyone ever thought of retro-fitting an existing engine to run diesel or such?

I know the compression is much higher and so is the wear on the components, but with a little tweaking, and swapping of parts, a somewhat reliable diesel engine could be made out of an already existing engine?

Possibly starting with the infamous Harbour Freight 79cc 2.5hp engine that goes for around $80 with the 20% off coupon...

Any thoughts on the merit of this idea?

Anyone know of an engine (small cc) that could be converted?

I'm sure that it is possible but the labor costs will not make it plausible. The compression would at minimum have to be raised to 200%. The piston, rod, crank, and bearing would need replacement. The gaskets and head-studs may need replacement. You may even need reinforcement done to the sleeves. After that, some sort of correctly timed direct injection would be needed.

 

[velosolex]

I think the whole thing is quite un-doable. As mentioned, engine components needed for the up'd compression ration are not available and injection is to expensive. Heck, even diesel engine manufacturers are going towards common rail systems to reduce cost and simplfy means to control emissions.

Cris