Big stroke 55 cc one cylinder ICE

Alex,
Wanted to let you know I'm following along. It's also a bit larger than my Val at 1.125 X 1.1 inch bore & stroke. Are you intending to use splash lube? If so seal it well with silicone and it should be all right. Good progress, look forward to the rest as it progresses.
Art

May I ask why you've chosen to have the exhaust valve smaller than the inlet valve? I would normally expect it to be the other way around.

AS

Thank you all. Roger, my lathe isn't very big one, but with some hint and tricks it is good possible to make a larger engine. I am amazed that the lathe engine continues to rotate larger diameters and harder metals. While the electric motor only has an eighth horsepower of power and some 1.6 Nm torque.

At the moment bottom part is almost finished and I am busy with making valves and seats. Later this week I will upload a little more of the progression.

Art, splash lube is a good idea. But I had in mind to use an existing oil pump. From here I planned to build a pipeline that could lubricate the big end and the cylinder wall as well as possible. But I am open to suggestions. What is the best way to design a splash lube? And yes I want to seal the whole carter with silicone, and add two seals for the axles (15 mm).

Allen, there are two reasons why the exhaust and lift are smaller than the inlet. You want that the engine could breathe easily, that is called the volumetric efficiency. The intake air-fuel mixture is coming in the combustion chamber with a low temperature and pressure. But for the exhaust, the gasses leave the chamber with way more higher temperature and pressure. Because when the exhaust start to open, for a short moment the exhaust gases leave the combustion chamber with tremendous speed. Then the piston moving upward and pushed the rest of the gasses and ensure that the new mixture enter the chamber.
In view of this, the speed and density of intake and exhaust gasses aren't the same. So they needed a different opening to leave the combustion room.

Secondly you don't want a large exhaust valve with also larger mass. The main reason for the size difference is to avoid pre-ignition and knocking. Against that knocking will not be so problematic with a compression ratio of 6:1. But the exhaust valve is the hottest part of the engine. We also know that Q=m Cv dT.
Hence the heat generated is directly proportional to the mass of the substance. Now if the size of the exhaust valve increases, its mass increases. So the heat of the valve increases.

Now after the exhaust stroke, the charge(air and fuel) is sucked in for the next cycle. If the temperature of the exhaust is very high it may cause pre ignition.
Also even if the temperature of the valve is not that high, during compression the charge becomes more volatile. The exhaust valve will ignite the charge creating a flame front which progresses in all directions. Also the spark plug creates a flame front. When these two flame fronts meet, knocking takes place.
To avoid these difficulties the exhaust valve size is kept smaller than the inlet valve. Correct me if I'm wrong.

Here some big update from the progress of December-January to today!

Crank pin journals with fitting an big end Ø 20 mm x 14.

Left and right main journals Ø 15. For the journals, I have milled some flattened piece in certain places. This to better fix the flywheel, distribution gear and oil pump later on.

Last picture shows two extra weights (4.7 gram) for the counterweight. This to fully balanced the rotary forces of the crankshaft and connecting rod assembly.

A couple of main bearing 'blocks'. Each fitted with a 6202 bearing.

Then the crankshaft press assembly. Had to make a tool to mount the crank cheeks in parallel. The result was just fine!

Crankcase progress to fit crankshaft assembly! Need more adjustment in the future to run it smoother. But it is fine for now;)

Added some spacers for the mounting plate for timing belt rollers and flywheel support bearing. The hole to fit the main journals in the front and rear crankcase plates, are 25 mm. This to put some seals for the journals.

Now it is more serious work! Valves and valve seats.

Valve stem of round 5. And the valve dish of staff material round 35 (needed for cams).

Third picture shows the result of solder at my home, but this was not good enough (heat to solder brass). So I had to do this with an autogenous welding machine set. I was lucky they had such a set at school. I thought the result was fine, for the first time I soldered hard (with some nice help tips from the workshop teacher !).

Modify valve disks. Before I install the valve seats in the head. I adjust the passage of the inlet in the cylinder head.

The seats and valves fits great so far. What a birth! This was done yesterday. Now need to fit some valve springs, camshaft assembly etc etc.

Alex

As an attachment you see a section of the cylinder head with valves assembly.

In red the connection between cylinder head and valve stem is shown. In blue, the connection between cylinder head and valve stem guide bushes is shown.

For the exhaust, the valve stem guide bushes fits nicely. But for the intake they are way to lose.
I had expected the milled hole to be small enough. I thought to make some sort of assembly bus. Where the bearings can be mounted more tightly. Outside diameter 10 and inside 7 mm.

Another thing is that the valve stem and the connection between the cylinder head has some slipstick-effect. Simpel solution would be to make the diameter in the head slightly larger. But I don't want that the exhaust gasses flow directly along the valve stem. Possibly I could make a guide bus for this. Maybe have someone any suggestions?

Two thoughts:

1. Are you sure that hard soldering will be sufficient for the valve heads, especially the exhaust valve? I have made my valves in one piece from stainless steel screws.

2. I have used one piece bronze valve guides with the outside diameter the same as the port.

Roger, the temperature of soldering is around 900 degrees Celsius. For exhaust valve it might been critical. After some research on the internet, I saw that average the inlet valve would run around with 425-540 degrees Celsius and the exhaust 650-780 degrees Celsius. But this engine is not going to deliver high power and peak temperature.

I saw this method from youtube, so I give it a try. But your way of making a valve of a stainless steel screw is also great idea! I think it will be good enough for the first tests. But thanks! Maybe in the future I will turn out of one piece of material. For now I used material silver steel (115CrV3 I guess?), it can be hardened to 64 HRC.

The red area in your drawing looks like a problem area to me - but you might get away with it in a low power engine.

Good full size practice dictates that the valve guides ends either flush or a few millimetres inside the port / channel and inside the spring at the other end. This gives you a big enough support area for the valve stem. The clearance between the two are measured in um (micro-meters) - most of my bikes has been in the 25-55um for the inlet and 40-70um for the exhaust valve.
The engine will run with a much bigger clearance and I don't expect this kind of tolerance on a model we make - but the size of the tolerance has great influence on oil consumption if you have splash lubrication of the valves ....

The reason I don't like the red areas are heating of the valves and the cylinder head on the exhaust side and more wobble of the valves - but again, probably not a serious problem here.

Best wishes

Per

Hi Alex, that will be big engine, will you try to power something with it once finished? (bicycle perhaps)

Per, indeed the red areas could possibly cause problems if the valves get really hot. But what you said, it won't be a high power en fast running engine. For the inlet, I have fit in some extra tube to fix the guide bushes better(shown pic. 1). And I had to make the red area slightly wider. I didn't measured the clearance between the stem and bushes, but now for both stems moves nicely. Fifth picture shows the valve assembly fit in the head with two springs. Lock the valve spring with a seeger ring 55 mm. I do not expect any serious problems, maybe I should make a firmer clip.

The spring constant is 3.63 N/mm. Reduced mass of valve train would be around 100 grams. So the own frequency of the spring with the mass would be around the 4000 rpm. This is higher than the max rpm what I would be running this engine. The spring length when the valves are closed are 8 mm. And for the intake 8+4.5 mm. Forces are not that high (29 N closed, 45.5 N opened), but I think it would be good enough to run it with low rpm range. The cam followers are carried out with rollers. With this and that it does not have to transfer many forces, I think it would be not that necessary to splash lubrication. Occasional greasing with ball bearing grease seems sufficient. Is not that right?

Perry, I have many this in mind to upgrade and to adjust etc. But first I want it that it run good with as a stationary machine. Later on I would make a hydro dyno (load cell), added some sensors like temperature speed etc. I have ideas to advance a programmable (mechanical interaction) ignition. In addition, maybe a throttle controller. Going to nearby convenience store with powered your own build engine to get some beer would be a dream! Maybe to attach this engine to a gearbox of a chinees motorcycle or a Puch moped engine in the future.
But this will come later! First plan is to start the engine properly;)

Yesterday started making the mounting beam of the camshaft composition. Two ball bearings 608 would be mounted in this beam. The intake cam comes to the left of the beam and the exhaust cam on the right. Also, two pairs of adjusting blocks are mounted on this beam where the valve clearance can be adjusted.