Boiler help for half breed steam engine

[the-mitchster]

guys i dont know if i posted this in the corect catagory. Im building a steam engine from a old 3 horse briggs. all i did was add a lode on the back side of the cam 180 degrees from the original. it runs like a top i couldnt be happier, but! right now its running on compressed air. i need some advice on a boiler im trying to stay away from firetube presure vesil boilers, im looking to build the smallest monotube boiler that will run this engine. i also need help with methods of feeding water to the boiler without depresurization..... posibly water injection or a pump ran by the engine. anything you can tell me is verry much appriciated!

[Allen]

What oil are you planning to use in the crankcase when running on steam? Regular motor oil will turn into a nasty white sludge in short order. There is a special oil for use in Troy, and other enclosed crank steam engines (of course, I can't remember the name at the moment ) that resists mixing with the water. IIRC, it's a bit spendy, though.

[the-mitchster]

i have been useing way oil from the school's machine shop but i havnt been filling the crankcase theres no point a quick few drops in the air suply line keeps the entire engine lubed (almost like a phneumatic air nailer) this thing will realy pur, but my biggest problem is air suply it runs my lil compreser dry in about 2 minutes. i realy want to build a mono tube boiler for it but have no clue how big to go i am in the proces of makeing it more efficient and i have been successfull so far but it's still an air hog if u will

[Gil Garceau]

A few drops of oil in your air or steam supply will not lubricate your main bearings and rod bearings. You might want to get a book on proper boiler building and check your state's boiler code.

[jht1057]

I know you have your mind set on a monotube and don't want to be bothered with multi-flue tubes, however, I would recommend a multi tube boiler.

A hand pump can be used to put water back into the boiler under pressure and there are 12v pumps that will also pump under pressure.

Need to have a little more information to consider boiler sizing, mainly diameter of bore and length of stroke. Plus what you would like to do with the engine, just run it or actually drive something with it.

Jim

[Andrew Mackey]

The typical 3 HP Briggs had a 2 5/8" piston with about 2 1/2" of stroke if I remember right. You would need a pretty large boiler to fill the volume of the cylinder, also valve timing would be different for proper.steam operation.. Contrary to popular thinking, steam pressure does not do all the work in a steam engine. Expansion of the steam is what does the work. Steam is admitted to the cylinder at TDC, yes, but pressure cut off occurs at a certain time to allow the expansion to do its work. The exhausted steam comes out at a much reduced pressure as the expansion energy is used to provide power. Get yourself a good book from a library on steam engine theory and construction, and you will see what you are up against.

Oil emulsification in the crankcase will be a big problem as steam gets past the piston and rings. On steam engines, the pistons use a 'water ring' a groove cut into the piston to help seal the piston to the bore, and usually the crankcase is open with independant lubrication to the bearings One thing that you might do to curb steam (and air for that matter) is to use neoprene or teflon rings, to positively seal the cylinder. This change alone will stop a lot of the loss you are getting from the ring gaps. Piston clearances on a steam engine are also much tighter, as the piston and cylinder do not get as hot as the regular gas engine does running on gas. Another item, is that heat loss is a no-no on a steam engine. The cooling fins on both the head and the block need to be removed, and the assembly needs to be insulated! More to think about.
Andrew