aviation fuel for 4 stroke engine?

[blockmanjohn]

Hi,

I have completed Jan Ridder's scuderi cycle engine. As of yet it will not run except for a few "pops" here and there. I am fairly sure that the problem is low compression. This engine uses no rings and relies on a very close and smooth fit between the piston and cylinder. He suggests no more than about .0004 inches clearance. Mine is a bit more than that, maybe 5 or 6 tenths.

My plan is to cut a groove in the pistons and install viton o-rings. The problem is that there is no oil used in this engine. High carbon cast iron for the pistons and cylinders is all it uses.

Is it possible to use an aviation type 2 stroke fuel which contains oil and possibly some nitro? Might it be better to just add some 2-stroke oil to the coleman fuel that I am using? Could it run with no oil in the fuel?

I guess I could just experiment with different fuels and see what happens, but I would really appreciate any input I can get from those who have more experience than me in these matters first.

Thanks in advance, John.

[Roger B]

Most of Jan Ridder's engines require a very good piston/cylinder fit. How did you finish your cylinder bores? What happens if you squirt some oil into the cylinders and give it a try? The working cylinder can be dosed via the sparkplug hole, the charging cylinder may require some dismantling.

[blockmanjohn]

I lapped the piston into the bore with 1200 grit paste. It seemed to be a very good fit, but I guess not good enough. The oil squirt is a good idea, but I don't want to dismantle the charging head and risk losing the seals which took awhile to make tight. Thanks for your input.

[blockmanjohn]

Is it possible that I didn't clean the surfaces of the compound well enough and the piston clearance continued to get bigger as I tried to get it running using an electric drill?

[Roger B]

Difficult to say  I lap my bores with diamond paste and then clean them in an ultrasonic bath. Try with just an oil squirt in the power cylinder, the pressures there are higher that in the charging cylinder. Jan Ridder is always open to questions from people who are building engines to his designs, he wants them to work.