6,23cc 2 stroke engine

[Kevork BOYACIYAN]

I'm continuing to send photos for crankshaft. After heat treatment its time for grinding the shafts and open the inlet port with appropriate angles. There isn't any picture for finished parts for now. The last photo shows a circular conic shape. I saw it on lots of rc engine advert. I think it's help to pulverized and seperate of fuel. So I just added it on mine.

 

[Kevork BOYACIYAN]

Now It's time for timing. I'm sure there will be many criticisms of positive or negative. Please do not hesitate to share them with me, all your comments will help me to modify my engine and get more power and efficiency from it. I'm already finished my engine, but I'll try to make changes.

1 TDC

2 TDC+114 EXHAUST OPEN

3 TDC+119 TRANSFER OPEN

4 BDC

5 TDC-129 ROTARY VALVE OPEN

6 TDC-119 TRANSFER CLOSED

7 TDC-114 EXHAUST CLOSED

8 TDC+29 ROTARY VALVE CLOSE

 

[lohring]

4140 is an excellent choice for a crankshaft. Do you have a heat treating furnace? While I have used similar steels that come hardened to Rockwell 35C, you can get a lot more strength with further heat treatment. Most small high performance engines are stiff and strong enough to not need your rear crankshaft for extra support. Any reduction in friction is critical in a small engine. I was once told that the cylinder to piston fit was the most important factor in a model race engine. That's why the experts spend so much time with that one factor.

Lohring Miller

 

[lohring]

Your timings and port sizes are too conservative for a tuned pipe engine. However, I suggest running the engine as designed and making new piston and liner combinations with more aggressive timing. You can run the engine on a test stand with a series of propellers. An optical tachometer can measure the rpm. Small changes in rpm with the same propeller are a good measure of power improvements. We used an inertial dynamometer which will give actual power curves under simulated racing conditions. That's only a little more complicated.

Lohring Miller

 

[Kevork BOYACIYAN]

I'm so happy to hear from you. I do not have any heat treatment furnace but in my factory that I worked since 25 years, we have lots of suppliers, which we send our molds for heat treatment.
Since I started this thread, I've been researching more about the rotary valve, especially the bell valve. I also found the following link that you and Jim are talk about valves.

http://www.modelgasboats.com/forum/...stions/20812-rotary-valve-or-zimmermann-valve

I will consider your advice, I'm not happy some parts of my engine, even before first run, because of quality of parts machining. I will make a new piston and cylinder liner set with new angles, also I plan to change cranckshaft. Maybe a new design which contains bell valve why not. But before make some modifications, I run it in its original condition first, which I already finished, to can compare the differences.

At least is my angles are enough to run this engine? Or not.

 

[lohring]

Some good, but conservative, timing numbers for a tuned pipe engine are exhaust opening 90 degrees after TDC; transfer opening 120 degrees after TDC; intake opening 140 degrees before TDC; and closing 60 degrees after TDC. Your engine should have at least two transfer ports on the side with a boost port directly opposite the exhaust. The exhaust port can be 70% of the bore width at the top with the transfers and boost port taking up the rest of the cylinder circumference. The boost port can be as small as 30% of the bore. The boost port should have at least a 50 to 60 degree up angle to aim the flow toward the cylinder head. The boost ports should have a horizontal discharge angle with the edges aimed toward the center of the bore away from the exhaust.

An even better design is in the pictures below. It uses 4 well shaped transfer passages to control the flow much better. Here the transfers have an up angle for better scavenging. Note the horizontal angles as well as the vertical angles. The language is Dutch. Also notice how large the crankshaft intake diameter is. These port sizes is what you need for performance.

We did some development on a larger, ringed piston, gasoline engine. There the port widths are dictated by the use of a ring. The engine was far from an ideal design, but you can see what we did to improve it. You may be interested in a series we did on fuel testing as well.

Lohring Miller

Lohring Miller

 

[xpylonracer]

The MB40 engine shown above is used for FAI F3D class pylon racing, these are radio conrolled model aircraft that are flown for 10 laps around a triangular shaped course marked out by 3 pylons, total race distance is 4km and best recorded time is 56 seconds.
Lohring mentions the large port through the crankshaft, the venturi intake is limited in cross sectional area to that equal to a 12mm diameter hole, this rule is used to keep the model speed down to a level considered safe for control of the aircraft.
Current model of the MB/Picco engine has a radiused piston crown with a matching radius to the cylinder head squish band.

xpylonracer

 

[Kevork BOYACIYAN]

Hi Lohring, don't worry I found some english version of diagram. Now I try to understand each angles.
αdir = angles of direction which shown in top view of cylinder, I already marked them on picture.
αup = inlet angle at the cylinder liner wall.
αpos= There is two angle and I can not figure out them.

 

[Kevork BOYACIYAN]

I want to send a couple of photos and pictures about my engine block.

 

[Kevork BOYACIYAN]

As always, the aluminum rod was first machined on the lathe, then fixed on a shaft and the outer surface was processed on the CNC milling. Used a reamer to finished the crankshaft hole at the end.

 

[lohring]

Let me post pictures of the port layout of the Aprilia RSA 125 cc engine. This is considered state of the art for motorcycle engines and requires a tuned pipe. It has a ringed piston. On a ringless piston engine you don't need the dividers in the exhaust but you probably can't make the exhaust width much more than 70% of the bore. Some engines have used a central exhaust bridge to get around this. The up angles and port opening timing varies depending on what you want the shape of the power band to be. For mid range power the transfer angles from front to back should run 25/10/55 degrees up angle and the open duration should run 125/128/129 degrees. For peak power keep the same up angles but the open durations should reverse the stagger with 128/125/125 degrees. You won't see the effect of this level of detail without transfer passages shaped like the Aprilia pictures. Typical model engine transfer passages can use the angles and timing I mentioned previously. See the liner pictures in the CMB article for more typical model engine porting.

Lohring Miller

 

[Mechanicboy]

The timing is too close each other in exhaustport and transfer port, it can create overpressure in crankcase by pressure from cylinder. The exhaust port must be open earlier before transfer port to reduce pressure in cylinder before transferport. Can't works well with tuned pipe with the close timing of exhaust and transfer. The transfer port on the cylinder must be wide as port. See the drawings of cylinder where the exhaust port is higher than transfer port as Lohring showed in earlier post #26 and #31.

See the animated engine with tuned pipe how it works in this link.
http://2strokeengine.net/2strokeenginetuning/2strokeengineanimation.php

 

[Kevork BOYACIYAN]

Hi Lohring I realized αpos meaning. It’s marking the intersection points of the ports beginig and liner wall angularly. Because the bore (21mm) is same with mine, I can use directly this angles and dimensions, which you send in blue picture. I will try to draw a new liner with four transfer and one boost ports from the beginning as applicable to milling without any casting proccess.

Hi Mechanicboy, I thoughted that it is more good to keep presurized gases in the cylinder as more as possible to get more power from engine. So I designed to open exhaust port as later as possible from TDC. But an engine with high RPM like over 20.000 there isn’t remain enought time to scavenging.

 

[Mechanicboy]

Hi Mechanicboy, I thoughted that it is more good to keep presurized gases in the cylinder as more as possible to get more power from engine. So I designed to open exhaust port as later as possible from TDC. But an engine with high RPM like over 20.000 there isn’t remain enought time to scavenging.

Not only pressurized gas in the cylinder to get more power.. fault timing will reduce the perfomance of the engine. The velocity of gas through the shavening port is in fact much higher than hurricane then shavening is not problem when the timing is correct.

There is the program who can be downloaded in this link how to calculate the tuned pipe vs timing.

https://www.mh-aerotools.de/airfoils/javapipe_en.htm

 

[Kevork BOYACIYAN]

This is my cylinder design, which I try many drawings before processed. Also I was a few mistakes in the production phase. The photos are belong my third attempt. This one also have a little false but acceptable. One noticable false is exhaust pipe connection hole. There is two canal inside the cylinder, they are combined with canals on the liner and creates transfer ports. After all I have learned, I agree that there is just two transfer ports and all of there ports are small.

 

[Mechanicboy]

And where are the boost transfer port?

 

[petertha]

Interesting build, following along.
Is the crank pin to be integrally machined or a separate insert? Can you describe some features on end of crank pin - the flat (for connecting rod retention) and the circle close to the web (lubrication hole maybe?). I guess we will see, but are you planning to finish grind or lapping or...?

 

[Kevork BOYACIYAN]

Years ago when I was searching on the internet I found the following picture and some articles which explain loop flow advantages. Also this type liner is easy to produce for me, this system use flat piston and just three ports are enough. I benefited from this picture and decided to make my liner as same as.

Hi petertha, thanks for your question. My crankshaft consist of two parts, long one is the main shaft and it is single part. First I processed it in lathe then processed on CNC milling to complete eccantric pin and balance part on it. I left a pass on all of surfaces for grinding process and remachining. I sended my crankshafts to a firm for heat treatment process. Then my crankshats are grinded for bearing assembly and or inlet port, without eccantric edge. Then I put them again on CNC milling to finished eccantric parts in appropriate dimensions. So I complete them like this way. There is an angled hole for lubricate the connecting rod needle bearing on eccantric part. And there is a flat surface on eccantric part edge, also there is a flat surface in the hole of short crankshaft. So they are angularly connected in right position, in the block.

 

[Kevork BOYACIYAN]

This is my cylinder head, I drawn many models in time this shape is the last one and I produced it.There is radially six holes for fixing. Its shape not continue to up but down. So the heat sinks are placed around the head. I was send my cylinder picture above, it have plain outer shape without heat sink. Cylinder head have quite big hole and it is totaly gets cover both cylinder liner and cylinder.

 

[Kevork BOYACIYAN]

It have a little conic combustor chamber with a radius at the corner, so I machined it completely on CNC milling machine. After inner surface I processed head of it by CNC milling and circular heatsinks by lathe.

At the end I needed a tap for my glow plug, but unfortunatelly I didn't have it. So I decide to make a tap, it have 0,794 pitch approximiately 0,8 acceptable. I have 52Hrc hardnes materials it can be machined on lathe with diamond tools. I build a tap then sharpened it and use this tool, it can seen on image 8380.

At last photo there is my head with connected glow plug on it.