mini v-4

[rcmachinist]

hello
how is everyone doing today. i am interested in building a miniture v-4 2 stroke engine i have started to draw some rough dimensions and started to work out some of the plans. currently i am in japan with the military so i am not around any machinery but i am trying to get all the plans done. so far my plan is to have a 1" bore and not sure about stroke yet thinking about 3/4". the cylinders will be based off of nitro RC car engines in the means of having 4 ports 1 big exhaust 1 big intake and 2 lubercating slots for the fuel to get to the crankcase. the carb will be a top mounted carb unlike a RC engine. The suction of the piston will draw the gas into the cylinder just like a rc engine. the will be no rings. the cylinders will be tapered for compression again just like a RC engine. Of course it will work off of a glow plug so no need for any cylinoid or anything. i am trying to keep the total engine under 7" long due to the fact that i am also working on a pre runner truck for it to go into. i have not started the real details on the truck yet but i am going to build the truck around the engine. i am getting autocad on my computer right now so i can start actually drawing the actual plans up for the engine first. If you have any Ideas thatmay help me out please let me know. thank you


RCMachinist
LCpl Navarre Justin J
USMC VMFA(AW)-224
2111 armor

[Stepper Monkey]

It is an unfortunate fact that the simpler the engine in number of moving parts, the more frighteningly complex the actual design is. While four-stroke engines may have a lot of complexity in the parts, the fact is they have a very broad range of variables under which they will still run.
In contrast, while the two-stroke, as well as some other engine designs without valves, looks very simple, the operating principles are frankly INSANE. Particularly the shape of the combustion chamber and the expansion chambers. The math involved in designing one from scratch is very, very formidable, even for a large corporation with a well-funded team. Even just designing a new exhaust system for an existing motor is a non-trivial task - everything is interconnected and the exhaust systems convergent-divergent shape serves much the same function as a camshaft as well. One of the reasons for this is that the fluid dynamics equations are all that really keeps the engine running. The pressure differentials are what are acting as valving and timing. Getting proper primary compression, moving that charge into the combustion chamber without losing it out the exhaust port or trapping too much combustion gas, getting proper combustion, and getting it to exhaust itself properly is not something I would suggest that any individual, no matter how skilled, could do from scratch.
I used to build and tune two-stroke racing engines, and even tuning and alterations to an existing design is an extremely technical science in and of itself. There is a reason two-stroke engines have lagged decades behind four-stroke development, even with people the likes of Honda having been working on R&D for decades so far.

I wish you the best, but this is not as easy as it might look just from the raw parts machining perspective. The parts are easy, calculating the exact dimensions to actually work are not!

[rcmachinist]

thanks for the input and i have now started to actually draw the block on auto cad and changed it to a v-6 due to measurement reasons.i know the exhaust and getting the right position on he chambers are going to be a difficult task but if it was easy what would be the point in making it. i have made expansion chambers before and know them pretty well i have been a rc hobbiest for roughly 10 years now and have done alot of work on my little toys. so i think i am up for the challenge. i know this is no small task and it will not be accomplished over night and neither have the other projects i have made. thanks for your cacern but i think i can handle it.

[elmerfud]

If I were you I would buy 4 or 6 used edge trimmer motors so your barrels, pistons, conrods, carbys are sorted. The trouble with a V type two stroke is the crankcase pressure in one bank of 2 pistons only charges one cylinder with pressure and the trailing cylinder only gets a sniff. Detroit diesel v8 motors overcome this with a supercharger, it works pretty crap though.
a boxer motor or inline would be easier or an offset crankpin crankshaft could fix it.