need an explication: I have an mvvs gas engine that runs well with 3% oil in fuel, I also have some glow engines that need 18% of oil, the most obvious difference between the gas and glow engines is the needle bearig on the big end's conrod on gas engines while glows has plain bearing. I also own a cmb 91 evo 2000 (glow) that has the crankshsaft bearigns one in front and the other in the back of the engine ( the crank journal is in the middle with roller needles). I am a little puzzled: why is not possible to use a fuel with low oil content (2/3%) in glow engines with a roller bearing on conrod?

My understanding is because the wrist pin has a plain bushing on a glow/nitro
engine, it needs all the extra oil for it to survive. A gas engine with roller berings
on both ends of the rod only need the regular amout of oil, which is 5% or less
depending on the type of oil used, and the application.

FBD.

Hi!
It's no problem running 2-3% oil in a glow engine if the big end have roller(needle) bearings...people have done so for years.
Remember the Swedish 18cc DAMO boxer twin from the eighties which required only 1% oil in the fuel.

Regards!
Jan K
Sweden

The obvious question has to be:
Why don't our glow engines have needle bearings?

Hi!
One answer is: They cost to much!
Another is: they don't hold up that well in our hi rewing engines.


Regards!
Jan K
Väsby MF

If you modify those gassers to run on methanol, usually only a carb swap, and run it on 2-3% oil, it will fry on the first or second flight. That is because gasoline is made from oil, and actually has some lubricity from small amounts of oil, and the large numbers of differant molecules. Methanol has very little lubricity and is has the same molecule, so they tend to pack together. You have to increase the oil content to about 10% on the gassers when running alcohol.

I think, besides all ,oil is helping the cooling of engine while leaving engine some unburned.Especially castor.

In addition to lubricating the engine, the oil also helps seal the piston. In ringless engines, the capillary oil film between the piston and cylinder provides the compression seal. You can sometimes milk a little more life out of a tired old engine that has seen its better days by using an extra high oil fuel. The extra oil seems to help the engine seal the compression better.

some glow engines do have neddle bearing on conrod but if you try to use 3% of oil thy will melt in no time

If my memory serves me correctly, the old Dooling 61 racing engine had roller bearings on the big end. The McCoy 60 had bushings, and could beat the Dooling in UC speed, but the Dooling was the engine of choice for tether cars. Both needed at least 20% castor oil.

Phil