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Lowest amout of oil runnable?

Old 10-15-2009, 01:56 PM
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Default Lowest amout of oil runnable?

I see fuel as high as 18% and as low as 8%, but when I think about bigger 2 strokes it's like 2%. I know that it takes less gas to produce the same ammount of power as methanol, but why is it so low compaired to these pretty small engines?

So basicly what is the lowest you should run these little things at?
Old 10-15-2009, 03:40 PM
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Default RE: Lowest amout of oil runnable?

It depends whether you mix with methanol or with gas.
Methanol has zero lubricity and would clean all oil from surfaces. Gas in fact has quite a lot of lubricity, so needs less oil to bring it all up to par.
Methanol engines for that same reason have large surface bronze bushed connecting rods. Gas engines like needle bearings better, which need less oil. A needle bearing in a glow engine won't last all that long, unless the bearing is very moderately loaded.
Old 10-15-2009, 07:02 PM
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Default RE: Lowest amout of oil runnable?

Ah makes sense now, thanks
Old 10-16-2009, 06:48 AM
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Default RE: Lowest amout of oil runnable?

The size of the engine matters as well. The large glow engines can use as little as 9% oil. This is because the engine has less wetted area over the total displacement, so less oil is needed. Also larger balls and races have less distortion and thus smoother. Similar to large wheels work better in grass than small wheels. So there is actually three factors that I know of. Lubricity of the fuel, lack of needle bearings on con rod, and the scale effect of bearings and rings.
Old 11-12-2009, 05:49 PM
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Default RE: Lowest amout of oil runnable?

......and the quality of the lubricant.
Old 06-23-2010, 08:28 AM
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Default RE: Lowest amout of oil runnable?

quality of the lube is most important. You can get away with less than 18% in smaller glow engines as well.

All thats needs is enough of separation at start up to prevent metal to metal contact. Once the fuel and oil is in the engine its hydrodynamic lubrication that keeps the piston away from the liner. In fact, in small glow engines theres almsot no other lubrication regime used.

fuels has a high oil content because the engine manufacturers and fuel manufacturers don;t have an agreed spec to work toward. There is nothing like Mercedes Benz MB226 or VW 507 type specs to govern lubricant formulations and there no EN228 or EN590 to govern fuel formulation. So they er on the side of caution and over recommend the lube oil content. Trust me, some of these glow fuel manufacturers use fancy names for what is basically low or medium viscosity hydraulic circulating oils

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