gmedson

Hi Zvonko - I posted this information earlier today but it does not appear even though I am listed as the most recent contributor to the thead. Arrgh! Here's another try...

If your Zeiss Jena is 2.5cc, cylinder bore should be about 15.49mm. If 2.0cc, 14.01mm. Just unscrew aluminum cylinder muff and measure inside dimension across top of cylinder.

Speaking about the muff, your home-made one should work fine. This is not a critical part.

With regard to fuel mix, the old classic recipe is 1/3 oil, 1/3 kerosene, and 1/3 ethyl ether. That will work ok for you, but most of today's enthusiasts reduce oil to about 20 percent. Castor oil is generally considered the best to use. Also, 20 percent ether is usually enough. If you reduce the ether and/or oil, increase kerosene to make up the difference. Modern model diesel fuels also contain an ignition improver, such as amyl nitrate. Reduces compression necessary for ignition, among other benefits. Saftest and best way to add ignition improver is to get a can of the stuff from your local struck stop or auto parts store. Is used in full-size diesel engines, such as trucks. Note the amount of the improver actually in the can and do the math so you end up with about 1 1/2 percent in your finished fuel. Balance of fluid in ignition improver can is just filler, a mixture of low-molecular weight hydrocarbons. Portion this to the kerosene fraction in your fuel when calculating how much of the different stuff to mix up.

Hope this helps. Hope this gets posted...

Regards. -Gary