4cylinder 2 stroke

[2stroker4cyl]

im new to this and i want to build my own engine completely but i figured id start off by making a new block and bolting on jugs and pistons off 4 31cc roybi motors i just cant figure out if i should go radial or inline which would be easist to do and i need some tips on ignition systems and also some block casting tips i plan on melting a couple aluminum brigs blocks for this the main thing is i have to make the crank case as small as possible so i can get a good fuel air ratio i plan on possibly puting it on a small bike

 

[xpylonracer]

There used to be a powered wheel in the UK called Cyclemaster which replaced the standard back wheel in a bike frame, that was a single cylinder 32cc 2 stroke engine, so with 4x31cc you will have loads of power.
I would go with a flat 4 but there are many design criteria which need to be considered.
If you are a beginner may I respectfully suggest you start with a single cylinder so you have a successful outcome, I think if you try the 4 pots there will be some disappointment around the corner.
Emgee

 

[2stroker4cyl]

i myself am not experience but my grandfather and some of his friends are im 17 and i have always been fascinated with engines i did my first rebuild on a brigs 3hp when i was 12 i understand the mechanics its just that neither me or my grand father have attempted to build an engine before i was looking for tips on how to do so and i didn't mean a bicycle ive already built a frame and picked up a 4 speed transmission for it

 

[gbritnell]

The way a 2 cycle engine operates dictates that the crankcase be closed. That being said to build any type of multiple 2 cycle engine you have to follow that design. Many years ago Suzuki and Kawasaki made 3 cylinder transverse motorcycle engines. Each cylinder had it's own carburetor because it was basically 3 engines put together. I know there are other 2 cycle configurations out there but for the sake of simplicity and tuning if you want a multiple then this is the way you'd have to go. A radial 2 cycle isn't possible because there's no way to pressurize the crankcase to feed the charge into the cylinders, Unless of course the cylinders were built individually and stacked as separate engines.
gbritnell

 

[lohring]

The standard piston ported cylinder would be good as a starting point. Lots are available. I'm most familiar with the model gas engines that can be found at Dave's Discount Motors. You can find a twin cylinder RCMK engine and parts there to get an idea of how a twin is built professionally. The easiest 4 cylinder engine might be horizontally opposed with two opposed cylinders 180 degrees out of phase in a crankcase section like this. You would need to build the crankshaft, no easy task. There are lots of other approaches. An inline four with Cox cylinders can be found here. A V-4 configuration is here. With piston ported cylinders you wouldn't need the crankshaft valving, but you could block off the piston ports and use crankcase induction. Using the standard Zenoah (Chung Yang, RCMK, etc.) crankshafts coupled together in inline twins and fours has been tried. The press fit crank pins often twist so I would recommend a different crankshaft design. However, their connecting rods and bearings would be hard to duplicate, so I would still advise an assembled crankshaft.

Lohring Miller

 

[SixSixSevenSeven]

The way a 2 cycle engine operates dictates that the crankcase be closed.

Unless of course you wish to use an external supercharger of course, but that's just overcomplicating things, you'd have to worry about oiling etc then too which just isn't worth it. Still, a 2 stroke radial would be kinda funky, I wonder if some sort of centrifugal compressor could be integrated into the front of the block, planetary gearset driving it or something, but I digress, don't see any reason to build such a thing other than "because I can" (and I can't).



As for the issue here. You have to be able to walk before you can run. Its one thing to understand how an engine works, another entirely to build a new design, plus you have to machine parts too which is a skill in its own right. Start at square 1 with a small single cylinder engine and reserve the 4 cylinder bicycle for a few years later when you have the experience to pull it off.

 

[2stroker4cyl]

what if i closed off the bottom of the jugs with small metal tubing with a slit in the bottom for the rods with a small piece of rubber for the rod to go through and the tubes out to a carb located centrally between them or 4 individuals to create a small enough area for the vacuum to occur and keep the crank wet then the crank case could be bigger and for the crank i could do some precision welding and weld it ind some ball bearings with piston pre-installed with tubes in place and have a steel block that i weld the intake pipes to and i build the intake as small as possible and i take the system and set it on a mini test stand with the top and bottom and on and weld weights on the crank to balance it out and i also have a scale to measure the piston weight so i can have a guess at what weight to use and ill wind it up to as many rpm as i want and slowly go up in increments to have it completely balanced it would definitely be a great amount of work to do it that way what are you guys thought on that i know that it probably sounds a tad tedious but i don't plan on it happening over night and i have the original crank and its counter weights and it is not a reed valve type

 

[barnesrickw]

If it's just an exercise in attempting the extremely difficult, I say go for it. If you want a high probability of a running engine, I would first try a single cylinder, and study two cycle operation very well.

 

[lohring]

A better way to scavenge a small engine is with a stepped piston. Inline and radial designs have been done. See the Bernard Hooper engines or the radial below. However, you just stepped well out of the relm of using readily available commercial components.

Lohring Miller

 

[tornitore45]

A total of 128cc on a bicycle?
Plus, examine the previous responses carefully before committing to this project.