25 cc Horizontal Engine

[Roger B]

Having got my first engine out again and had a play there are many things I would do differently now so I have decided to design/build a Mk2. The basic design will remain but I plan a number of changes, some may be better, some may be worse. I will keep the original as it is.

1) Welded rather than riveted frame. Quicker and easier but may result in more heat distortion.
2) Conventional cylinder with wet liner rather than 'spool' with thin outer jacket.
3) Piston, cylinder and head made from cast iron rather than BDMS.
4) Balance weighted crankshaft.
5) Smaller valves that fit inside the bore.
6) Timing gears inside the frame.
7) Easily adjustable ignition timing.
Possibly narrow the frame.
9) Design the details of water passages, camshaft, rockers etc. before I start cutting metal.

During my last trip to China I had time to start my normal electronic back of envelope design and have also started to look at what materials I can relatively easily find.

Here is the youtube version of the original along with the original drawing, the start of the new design and the start of a lot of hacksawing.


<a href="https://www.youtube.com/watch?v=aE632WpWYns" target="_blank">http://www.youtube.com/watch?v=aE632WpWYns</a>

[Roger B]

A quick check to see if I can fit the big parts in the Keats. It looks ok but I will have to drill and tap a couple of fixing holes. It will certainly be more rigid/safer than trying to use 80mm chucks.

[b.lindsey]

Roger,
Glad to see you back at some engine work and will look forward to seeing how you incorporate the changes you noted into the new design.

Bill

[Roger B]

I decided to check if my ideas for making the cylinder jacket would work. The skin on the CI bar is quite hard and I found it difficult to get a good finish. It was turned down to 46mm leaving a mm to work on. The cut with the holesaw was much easier than expected. There was 4 minutes between the set up and finished pictures according to the camera. I was not happy holding the bar in the chuck alone to face off and cut the other centring groove so I got out my as yet unused fixed steady.
Problem  the hole was just too small and off centre so rather than being the hoped for quick job I will have to set up the keats to hold it on the faceplate.

[Roger B]

Completed with minimum swarf  I have got the cylinder body with a bore between 29 and 29.2mm (the hole saw was nominal 29mm) and a CI rod with a diameter of 25.5mm which will be used in the future as the cylinder liner and piston for another smaller engine.

[smfr]

That hole saw did the job, and now you have a CI plug you can use for other things! Nice work 

Simon

[Roger B]

I have roughed out the cylinder liner the same way with a 22mm hole saw. 22.5 mm bore, 18.5 mm rod (piston for the vertical engine?)

[Roger B]

Moving on a bit with the chunks of CI and had a go at roughing out some valves from a couple of A2 stainless M8 x 60 wood bolts (carriage screws or whatever you call them). I previously used A2 capheads but the places that were open today didn't have any big enough.

[fumopuc]

Hi Rodger, I like your idea  to make valves by wood screws very much.

[Roger B]

I received the part machined flywheel from RC. One side looks good, the other side is a bit eccentric but I think it will clean up OK.

I need to do a bit more design on the balance weights and then start on the crankshaft.

[Roger B]

Crankshaft underway. I drilled the centre holes using a technique I read about which seemed to work and is supposed to keep the centre holes coaxial.

This is on the limit for my lathe. I had to angle the compound slide 20° to get some cutting distance. The full cut on the webs required the tool to be repositioned twice.

As I am intending to fit balance weights there are two M5 holes in the webs so I made a bridging piece to clamp across the opening to help keep it all rigid when turning the shafts.

I have turned the crankpin to 13mm to allow some cleanup depending on how much the BDMS distorts.

[smfr]

Good stuff, Roger. That's a neat idea to keep things square while turning! You could even make the clamp piece T-shaped, with the stem of the T fitting into the slot to make things even more rigid.

Simon

[philjoe5]

I'm getting a good education on this thread Roger.  The picture sequence for the one piece crankshaft is great.  Something I haven't yet done but plan to.

Thanks for putting titles on your pictures.  I've saved them and will actually be able to find them when I need them.

Cheers,
Phil

[Roger B]

Simon, I didn't put a spacer block in this time as the webs are only rough turned. After it has finished distorting I will finish the crankpin and webs and then make a spacer block to finish off the shaft. It will be held in place by the bridging piece and some insulating tape.

Phil, thank you for the comments. As I reduce the size of the pictures before posting it's very little effort to sequence number and title them when saving, and also means I can find them when I am looking back over stuff.

[Roger B]

Crankshaft roughed out so it can sit and strain relieve before the final machining. I am still undecided whether to cut the webs square at the crankpin or to make them the same radius as the balance weights.

I decided that it was quicker to saw the waste away from the shaft than to turn it off.