Shuffling off this mortal oil

I read the letter from John Smithson in the November 2021 issue of OBM about worries with two-strokes and E10 petrol. I would like to add my thought as follows.

The upper cylinder conditions for a four-stroke are worse because petrol is a solvent and acts to wash oil from the upper cylinder wall. The piston rings have to balance sealing against letting enough oil pass to keep the piston and rings lubricated. Diesel engines last longer than petrol engines because the fuel is a light oil and so the piston has oil both above and below the piston rings.

A two-stroke engine is similar to a diesel in that the fuel is ‘oily’ whether the engine uses premix or oil injection so I would not be too concerned about the E10 effect on lubrication.

I have thought about this for my own Jawa twostroke. I don’t actually know if oil dissolves in ethanol alcohol, but even if it did not I came to the conclusion that fuel going through the carburettor jets and into the engine would contain the same amount of oil, it is just that all the oil would be dissolved in the 90% petrol. If oil does dissolve in ethanol it will act just like ‘oily’ petrol and won’t wash oil from the cylinder walls so no need to be concerned.

I was more concerned about the fact alcohol fuels need a much richer mix than petrol so the overall mixture will be a little weaker although not by a huge amount. I thought about this too and reckon that as 10% ethanol will lower the calorific value of the fuel – you would actually need to use a little more throttle to develop the same power so, if anything, there will be a little more oil going into the engine. That is my theory, I would welcome OBM readers’ views on this.

I am planning to run my Jawa on the Esso super unleaded E5 which is readily available locally and possibly buy 10-litre tins of ethanol-free ‘storage fuel’ that is now available to dilute the ethanol content down when I don’t use the bike much over winter.

I am planning to do some experiments in 2022, putting some E10 fuel in a clear jam jar, adding twostroke oil and then making a small hole in the lid to replicate the tank cap breather to see what happens during long-term storage, particularly if the mix starts to absorb water from the air.