[balsaman]

While it might seem as if I am doing nothing, I have been working on a twin by hacking two week eaters. Once this one is done, I will get back to my other twin.

[WOODKNACK]

how are you connecting the cranks together?

[balsaman]

I cut one off at the throw, then drilled and tapped it for the 10mm threads the other crank has on it's end. Locktight and a tapered pin hold it together.

Eric

[WOODKNACK]

looks good. keep up the good work!

[RotarySMP]

Could you post a picture of the final crank please?

[balsaman]

Yes and no. I needed to assemble the crank with parts of the crank case in there between the two throws. Now that it's permanently assembled, the crank can't be removed. I will take some pictures the next time it's apart for a closer look.

Eric

[aspenelm]

Interesting. I have a stack of mcculloch chainsaw motors that I want to do something with.

are you going to have one or two carbs? are there sync issues? I assume the crankcase housings are completely separate. Also what is the relationship between the first and second piston, is one at the top of the throw while the other is at the bottom of the throw?

[balsaman]

The crank cases are seperate. One carb, the pistons are 180 degrees apart. I need to work out the ignition. I may make one flywheel with two magnets, one magneto and an electronic ignition module.

Eric

[RICHARD ZASTROW]

You could fire both at 0 & 180 (- spark advance) My 3-cyl. fire all 3 3 times per rev. Only the one in compression actualy ignites.

[balsaman]

That's the plan...

Eric

[vulcom1]

After looking at your conversion I thought you may want to see what I have been working on. 2 Ryobi's for 60cc's horizontally opposed. I am now working on the ignition so I can start it to see if stays together. On the ignition (cdi) I am learning new things like programming a pic and think I may have aquired enough knowledge to get it done. I have had help on the ignition and now just working out some of the bugs when you change components.
With your ignition being 180 deg. differance in firing I would be tempted to install 2 magnets (180 deg.apart)for your pickup and waste a spark as mentioned. I am not sure if mine will have the output to fire 2 coils at the same time which I will have to try or install two systems in parallel. I have my board down to 1.5 x 2.125 so far.
John

[Arthur Clampitt]

You could fire both at 0 & 180 (- spark advance) My 3-cyl. fire all 3 3 times per rev. Only the one in compression actualy ignites.

I know this is done on 4 strokes with little problem , With 2 strokes the area around bottom dead centre has a combination of exhaust gasses exiting the cylinder and inlet mixture entering via the transfer ports ( Assuming that is the way these little engines work ) A spark firing might not be the best idea ?

[kentavv]

vulcom1 - looks like an aircraft cawling and wheel pants in the background of your picture... are you putting that engine in a plane?

[balsaman]

I know this is done on 4 strokes with little problem , With 2 strokes the area around bottom dead centre has a combination of exhaust gasses exiting the cylinder and inlet mixture entering via the transfer ports ( Assuming that is the way these little engines work ) A spark firing might not be the best idea ?

Hmm, hadn't thought of that. Anyone have any experience with this on a two stroke? I know it's done successfully on older 2 cylinder, 2 stroke, snow mobiles.

Eric

[vulcom1]

The engine is going on my scratch Raven (89") which has a modified Poulan46cc with cdi ignition. Waiting for some weather(warm) to show up but I think before that happens I will have the twin on it.
I think the wasted spark would be okay as the piston is before bottom dead centre as you are firing in advance of tdc the exhaust gas is still being removed and a fresh fuel mix is being pushed in. There is also no compression to help ignite the mixture. If mine was in that configuration I would try it first as it would be the easiest route.
Eric,
Have you got or figuured out your ignition? I have the hv end working but was having problems with the trigger.(scr) Comes from changing to different components(dah).
John

[balsaman]

OK so, been working on the ignition. There is no way I can combine two flywheels to make one with two magnets. Those flywheels are quite the mixture of steel, magnet, and aluminium casting.

The plan is to use the existing points, no magneto, an automotive coil and battery. I made a new cam for the points that slides over the old cam (ground into the crank shaft) that has two flats, 180* apart. So now I have the points opening and closing twice per revolution. I need to work out how to get the two plugs in series so they both fire 180* apart. I think this will require insulating the points from engine ground and using the engine itself to connect the two plugs electrically and the spark plug wire for the second plug will be connected to ground....Something like that.

Eric

[vulcom1]

Eric,
I am not sure but are you going to fly with this engine or doing testing? You mentioned automotive coil and twin points which gets heavy.
If you are flying I have made a few hub adapters and now have gone to the setup you can see on the nose of mine. The od is 2.25" so is not to big and I use the original key and nut internally to keep it on. The front part is bolted on with (6) 10/24 socket head bolts. Mine was done manually as I am not setup for cnc and is the reason I am here to maybe get into it. The back side of the hub is turned so the magnet is out of sight and I adapted on my case a split collar for adjusting the hall sensor. I think you could set this up just as easy as making the cam, cam plate and other items.
Just thought I would mention what I have been up to. I like watching for projects like this as I find it goes with what I am into.
Happy New Year to you and your family.
John

[balsaman]

Not planning to fly it, just display. In the end it will be water cooled with a radiator.

E

[RICHARD ZASTROW]

Ref 2-stroke spark ignited ic engines. Spark @ 180 & 0 works on 2 cyl. & 3 cyl. motors. I don,t know if 4 would be too close. There is a spark advance (I used 21 deg. btdc.) which allows some added margin. Properly tuned 2-strokers will have a narrow power band but when everything is timed (tuned) correctly, they produce buko hp. In a race tuned 340cc Rotax snowmobile engine with race gas (100-113 octane) no turbo's or superchargers you can produce about 115 hp. Thats 338hp/ltr. That includes, of course, the benefit of very dense cold air (lots of oxygen) which permits burning a lot of fuel with very high revving (11,000+ rpm) motors.
The racing gas allows advanced timing & high compression withought pre-ignition. Add to that the tuned exhaust of reverse cone pipes and you have volumetric efficency better than 100 % You should be able to do the same thing with your 2-stroke airplane motors. Read up a bit on the pipes though. It's very easy to loose pwer instead of gaining or even burn pistons if they are not properly designed. lol!!!

[balsaman]

Here are some photos. I hope you can see the pin used to secure the two crank shafts. Also the ignition and new cam.

E