6,23cc 2 stroke engine

[petertha]

Just a general observation that most engines I've seen, even in the HP class, don't usually have wrist pin end the same diameter as the crank pin end. It probably has to do with strength & reciprocating mass. I'm not sure which is big or which is small in your cad model (suspect the top end) or if bearings are driving these dimensions. But just mentioning. Lots of HP 2S glow engines have bushed wrist pin in methanol / premix oil fuel. My mantra is - if you don't fully understand it or cant calculate something better, best not to stray too far what others have spent their lives refining... at least for the first engine

Here is link to Jim Allen gallery specific to connecting rod. I doubt many people will deliver this kind of power to displacement. He has some other nice techniques & fixtures on the web page that I'm sure you will find beneficial
https://gallery.intlwaters.com/thumbnails.php?album=360

many more goodies from the same guru
http://www.modelenginemaker.com/index.php?topic=3890.0

 

[Mechanicboy]

And the other is the connecting rod balancing vs counter weight on crankshaft vs weight of piston who are important in the hi reving engine to keep engine in balance with less vibration by rotating mass. Use "Ctrl" and "+" to resize the image and read about balancing the conrod-piston and counterweight.

 

[ixb1]

Hi Kevork
Your build is interesting.I saw latest engine porting changes and have a question.You really need your engine running at 30000+ rpm?

 

[lohring]

Those rpms are pretty standard in a competition engine of that size, especially for cars. We ran 26 and 35 cc gasoline engines up to 25,000 rpm in lots of dyno tests.

Lohring Miller

 

[petertha]

That's what I mean. Your rod assembly looks like much more mass on the piston end; rod width, same/big diameter wristpin maybe meaty piston too. Is that what your calculations are confirming meets the balance equation?

 

[Mechanicboy]

As usual the model engine do not have the needle bearing in the connecting rod in their high revolution engines due the glow plug engine is really overlubricated compared with the big 2 stroke gas engine with 2-4% oil in gasoline (glow plug engine fuel has 12-25% oil in fuel). Use thin bronce bearing pressed into the connecting rod and the wristpin must be smaller diameter and light weight (hollowed wrist pin to example). Oil hole must not be in the pressure zone (see former post as i wrote). I used hollowed drill rod (silver steel) as wrist pin who are not easy to break off (uneccesary to hardening the wrist pin since abration is not problem).

How to press the thin bronce bearing into connecting rod:

1. Create the bronce with right width and diameter. Do not drill hole in bronze!
2. Locktite 648 applied on bronce bearing and press into the connecting rod who are made of aluminium 7075.
3. Drill and ream to right size for crank pin and wrist pin.

 

[Kevork BOYACIYAN]

Hi,
Because of the production took a very long time, I decide to had finished my engine completely or at least a large portion of it and did a lot of photo shooting, otherwise this article would be cut again and again. When I started sharing my drawings and pictures, I realized that they are many design faults or lack of quality. After your comments I'm back to my drawing table, and meanwhile I'm started to watch my completed engine on my desk. I am trying to make some corrections by making a minimum change on it. For example, changing of the input timing on the crank is easy. But the modification of the port, I sent yesterday, is a modification that needs to reproduce the cylinder liner and the piston together and reshape the existing cylinder. I will try this. But before that, at least I want to hear the sound of the running engine.

Dear petertha connecting rod have a very simple and symmetrical design. It doesn't matter to put it up or down side in the engine. In my first drawing, I used a bushing on both the wrist pin and the crank pin, but then I've converted them with needle roller bearings. It has "I" shaped midle part and machined in CNC milling machine at one time. I haven't opened the lubrication holes yet, so I still have a chance for the best solution. By the way I didn't make any calculations about piston-conrod vs. crank balance.

Dear ixb1 I had not planned to make a high rpm engine, maybe this design looks like that, or maybe it has this capacity, I'm not sure, but this is my first attempt and I don't have too much expectation from that.

Dear Mechanicboy I do really understand what you mean. We use bronze in our factory, where I work, with same method. I have hydrauolic hand press, I can pressed bronze in to the aluminium connecting rod and then procces it. I will try to make a new conrod with this way. Also it have that advantage to not do any heat treatment, thus help to keep stabil con rod.

I will try to make more sensitive engine after my first experiment and that knowledge that I've learnd from here.

Thanks

 

[RodRico]

Very interesting project. It interests me primarily because I am currently designing a form of two-stroke with cylinder volume of only 2.1 cc. These small engines bring all sorts of challenges, and I'm interesting in seeing how others approach them. I've been in design for about 3 years now. Most of that time was spent developing thermodynamic models complete with estimates of heat and friction loss. It's only in the last year or so that I started the mechanical design complete with stress, thermal, and flow analysis using Solidworks. My current challenge is the fuel injectors. I use them to inject directly into the cylinder after the exhaust port closes to end the scavenge cycle. Injecting in this fashion eliminates a number of problems, not the least of which is unburnt fuel in the exhaust. Because of the small displacement and the fact that I plan to run in Low Temperature Combustion regime (min 36:1 air-to-fuel ratio), I need to inject a maximum of only 0.00009 ml of fuel yet still develop good spray and mixing characteristics. I think I'm close to completing the design, but some of the features are so small (0.076 mm orifice and 0.254 mm needle), I'll likely have to send key parts out to a micro-machine shop. I enjoyed reading about your work thus far and look forward to following your continuing efforts. Keep up the great work!