Advices needed for CDI adaptation (2 stroke engine)

[TCAS]

Hello,

I am in trying to make this engine work. It's a MZ202 , twin ignition 2 cylinders
It came without ignition , I bought a pair of coils from the manufacturer (IDM)
But on this old model one 1 pickup can be installed , and 2 CDI are not fitting
I'm trying to find a equivalence , adaptable CDI + pickup able to feed the 2 coils , easy to find in aftermarket or used (bike , jetski etc)
Also need a power regulator , as rotor is only providing current for battery , no HT
I dont get how this system is actually "redondant" , one cylinder depending upon 1 CDI .. actually more chances to fail as they are 2
any help really welcome ...
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[Ian Rogers]

Moved your post here to Automotive section... You may get some hits here...

 

[TCAS]

Thank you Ian , I was hesitating as it's not exactly a car engine , but you're right

 

[shortbus=]

One pickup is all that is needed. The engine uses a "waste spark" ignition. This works because when one cylinder is on compression the other is on exhaust. Most newer cars and Harley engines from the start of V-twins used this method.

The redundancy of the ignition comes from the fact that both coils are fired from both CDI units. Each coil has a spark plug in each cylinder. That way if one CDI dies the engine still runs.

The engine needs a battery for the ignition. This is also for redundancy/safety in an aircraft. If the alternator fails, the battery will supply ignition for time to land safely. You don't say how your going to use this engine, but if for a aircraft, for your own safety and for the safety of people on the ground, the original dual ignition system and battery ignition should be kept.

 

[TCAS]

thxs shortbus,

my engine is a first version , and parts available are for twin pickup , which can't be installed on mine
Yes , it is intended to be an ultralight project. Rotax 447 is single ignition and even more reliable than 582 (dual) for instance , not saying that it's not bringing improvement but...
It really seemed to me that 1 coil / 1 CDI was for 1 cylinder , from what I can see in the 3 cylinders version for instance isn't it obvious? (or not )

edit : well I also found this picure , showing as you state
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[TCAS]

I can get the 2 CDI that are used on actual model , but they require 2 pickup .. how to solve this ... connect the unique pickup in parallel?...

 

[shortbus=]

Yes the single pickup is used for both CDI units. The crankshaft is a "flat" or 180 degree shaft, meaning when one cylinder is on compression/power stroke the other is on exhaust. The cylinder that is on the exhaust stroke the spark is still allowed but since it doesn't do anything it's "wasted". https://en.wikipedia.org/wiki/Wasted_spark

Most small (lawn mower, etc.) engines use this system. The points or in newer engines CDI, are run from the crankshaft instead of the camshaft. The crankshaft gives a spark every revolution, the camshaft will give a spark every other revolution, because the cam is half speed of the crank.

Here's another link to your engines operators manual -
https://www.compactradialengines.com/pdf/MZ202man0404.pdf

In it it shows the two CDI units connecting each spark plug.

 

[TCAS]

Shortbus , thanks for explanation , I now understand what is "wasted"
As you see on diagram , these DCI are made for connecting to 1 pickup each ... And I can have only ONE pickup due to the old rear case design ... that's why I'm still at the point to look for alternative
advance diagram is quite basic (a line...) , I really don't know who to adress to point me a reference for a CDI able to handle 1 pick and 2 double coils (that I just bought -not cheap from IDM)

 

[shortbus=]

Can you post pictures of where the pickup mounts on your engine? And pictures of the single and dual pickups? I assume that the pickups are the hall type, triggered by a magnet in the flywheel. I like solving puzzles like this.