Hard firing

[Gordon]

Thank you all for your input and suggestions. I have it running somewhat better but the lack of any means to adjust things makes it hard to make any appreciable changes. One of the main problems with this engine is the very marginal compression stroke. As I said the compression comes from one cylinder moving faster that the other so even perfect parts still make for marginal operation. I have made and remade parts for this engine several times. The pistons/rings leak no matter what I do. They even leak with o-rings but with o-rings it develops enough compression to at least run somewhat consistently. I have made at least six sets of pistons and 10-12 sets of rings and the results seem to be pretty much the same no matter which set of pistons or rings I use. Yes I have made rings using the Trimble method as well as other methods. I have also tried several carburetor designs as well as RC carburetors. Sometimes I am just too stubborn for my own good. I should have given up on this thing a long time ago.

 

[doc1955]

If you have tried O rings and that many tries with cast iron rings I would venture to say you need to do some work on the cylinder or the valves. I know this can be a bugger of an engine to get to preform. And yes the only way to adjust things is to make parts over. I still may try my hand at one eventually but I have other engines I want to build first. I need to wrap up my Mini Hog and then I plan on a few steam engines first. Anyway good luck and keep at it eventually you will get it that to me is what this hobby is all about.

 

[Mechanicboy]

These exotic engines can be painful to build without it will run.. I stay away from these exotic engines if there is not available information how to get engine running and how to faultfinding the trouble why the engine can't start up. When you saw the engine is running successful in YouTube, take contact with the engine owner who created the movie and get information how to and faultfinding the trouble.

 

[Gordon]

If you have tried O rings and that many tries with cast iron rings I would venture to say you need to do some work on the cylinder or the valves. I know this can be a bugger of an engine to get to preform. And yes the only way to adjust things is to make parts over. I still may try my hand at one eventually but I have other engines I want to build first. I need to wrap up my Mini Hog and then I plan on a few steam engines first. Anyway good luck and keep at it eventually you will get it that to me is what this hobby is all about.

I have lapped the cylinder and checked taper and diameter and I have made the cylinder a couple of times. The leakage shows up when I squirt oil on the piston skirts and turn the engine over by hand. As it gets to the end of the stroke it forms bubbles around the skirt so the problem is not the valves.

I have redrawn the beast in CAD but I have used 2D CAD for years but never learned 3D. I played around with Fusion 360 but never got proficient enough to actually use it. If I actually spent enough time on 3D I probably could move stuff around on the drawing to see what happens instead of remaking the parts. I am not sure if I want to spend that much time playing around with a computer rather than making chips.

 

[doc1955]

Are you sure you don't have an out of round going on? If you put cast iron rings in I personally don't like lapping the cylinder as the rings don't seem to seat well for me I like the boring marks left in and then running with another engine or an electric motor to seat the rings. I have had good luck doing it that way. If you lap it takes much longer to get the rings to seat. I also stay away from o rings but if you lapped and have o rings of the proper size they should seat.
I was a tool design engineer when I worked and we did everything in 3d cad I used NX mostly but I do also know Catia & SolidWorks

 

[Gordon]

Are you sure you don't have an out of round going on? If you put cast iron rings in I personally don't like lapping the cylinder as the rings don't seem to seat well for me I like the boring marks left in and then running with another engine or an electric motor to seat the rings. I have had good luck doing it that way. If you lap it takes much longer to get the rings to seat. I also stay away from o rings but if you lapped and have o rings of the proper size they should seat.
I was a tool design engineer when I worked and we did everything in 3d cad I used NX mostly but I do also know Catia & SolidWorks

It certainly is not enough out of round to measure. I have been in contact with another person is also building this engine and is having all of the same problems. He has had the cylinder professionally honed and has purchased commercial rings and he has all of the same problems.

I owned a metal fabricating shop where I designed and built industrial machinery, primarily material handling and position equipment. I designed everything using Generic CADD which is now Visual Cadd in 2D cad. I started using that back in the early 90's. 3D was not even available at that time and for the type of stuff I designed was not necessary. It was quite a change when I started doing this stuff. I went from +/- 1/8" was spot on to +/- .001 was normal.

 

[doc1955]

Yes 3d cad has been around well before the 90's. I worked in the tooling side f the shop since 1974 and retired a couple years ago. I mainly designed large hydraulic fixtures for nc machines and some progressive dies. Worked on stuff for the CH47 helicopter for the military just before I retired anyway thats all beside the point.

Well I can't give you any other things to check if the cylinder is correct the valves aren't leaking and only the cylinder is leaking without hands on I am out of Idea's at why your rings are not seating. Not sure what else you can try.

 

[Mechanicboy]

To check the piston ring is close to the cylinder with the tool + lamp. And how to grind the piston ring flatness.. The piston ring must have contact with groove in the piston. all must be smooth and flatness to keep tight against leakage. The ring gap in the model engine must be small as possible, not more than 0,2 mm (better smaller tham 0,2 mm, my gas engine with 24 mm bore has ring gap at 0,03 mm ), not much expansion in the small model engine without the ends of ring gap hit each other when the engine is in working temperature. (the book is from USSR, but i am norwegian. )

.

 

[Cogsy]

Jens - you have misread the dimensions in that book. It is suggesting 0.002 * Diameter so your 24mm bore should have a gap (per the book) of 0.002*24 = 0.048mm. Really though, given the tiny width of the ring gap that compression can escape through (only the sliver that protrudes past the edge of the piston) ring gaps can be reasonably large and not have any real effect on compression. A good rule of thumb which works well is ~0.004"/ ~0.1mm of ring gap per inch of bore diameter. Going smaller than this won't increase compression but not enough ring gap and having a bind is a very bad thing.

 

[Mechanicboy]

Jens - you have misread the dimensions in that book. It is suggesting 0.002 * Diameter so your 24mm bore should have a gap (per the book) of 0.002*24 = 0.048mm. Really though, given the tiny width of the ring gap that compression can escape through (only the sliver that protrudes past the edge of the piston) ring gaps can be reasonably large and not have any real effect on compression. A good rule of thumb which works well is ~0.004"/ ~0.1mm of ring gap per inch of bore diameter. Going smaller than this won't increase compression but not enough ring gap and having a bind is a very bad thing.

I know , my engine is not so hot when running... the table for ring gap Vs bore at my work place..