Detlef Kunkel

If you have a weak ignition ( cap, coil, plug, ECU or whatever) and it is a borderliner, you may well see sparks in any open test, but the spark will not come under compression condition.

Pros do have a compression chamber, set it under +5 to +8 bar of pressure and then check the sparks. That is much more realistic.

The ONLY thing you see and confirm in your way of testing if there is NO spark at all. A borderliner is much harder to get by.



I had one of my Moki 180s on the test bench, tuned it quite fine, stored it carefully away in my office ( not a damp cellar or so)

One year later mounted on the airframe- 2 coils were not working.

Checked a lot- the coils were not working any more. Cables, connectors etc- all fine.

Replaced the complete system.

2 months later- all 5 coils of this ignition were firing absolutely fine, even test flown just to prove - no issue.

I cannot explain this from the technical point of view. Maybe temperature, condensation effects, micro cracks in the coil insulation or whatever. I simply do not know exactly what it was.

And believe me- I checked that case VERY deeply.


You see in the pics that you are not the only one spending time with this topic.

I tried RCEXL Ignitions as I operate this brand very successfully on my own V4 Phoenix engines.

So I tried their radial ignition. It is not plug & play. I dont care, because if I replace the ignition, I wanted to replace it completely including the Moki sensor.

First I made only an adaption to the black Moki hub, in later engines I replaced the entire hub with a custom made one.

The ignition replaces the original coils, as Rainbow and CH do as well.

Needs to be adjusted to the correct timing (and then you even find a slight increase of rpm if you do it properly.


BUT:
This is not something you do without sufficient tools, machines and - of course- the necessary know- how. It is no quick plug & play thing.

BTW this is the third year I run these conversions, no issues so far


On the other hand- everything can fail.

I had old black Moki ignitions for 10 years, many flights- no issue ( running at precisely 5,5 Volts)

Blue ones failing during lunch break (ran before, no function after the break. Switched off of course (!) and nobody was touching the engine)

Everything can happen, that must be clear.

Detlef Kunkel

Correct. Try a gap of .35 mm.


But if this works and .5 mm doesnt, I personally would no fly that igition any more. One day or the other it may easily quit the function in flight when you do not wish so

Ragz

I would hate to send this back to germany because it's very expensive to send and importing it back would entail customs duty again. How difficult is it to replace the coil at home?

Detlef Kunkel

We cannot know or say what you can do and cannot do.

Basically- everything is possible.



Its not really a big fun and you should be experienced in soldering, but why not give it a try

Moki Radial Service USA

The hall sensor will not cause a single cylinder to not fire. I have seen solder issues it the bullet connector. May be worth a look if you have no spark. I have also seen coils that will make spark when testing but fail under load. If you have spark, It may be a good idea to check the compression also. Feel free to reach out if I can be of any help moki radial service USA @gmail.com

ChemE

Crashed MOKI 250 Repair -Some videos by -Oliver Rogeau - Page 2 - FlyingGiants

I am going step by step in the rebuilding process!!! visit if you want. I just do not have the time to do it on two sites.

Ragz

It just occurred to me, that I am using a 6v powerbox spark switch. Perhaps I should just bypass that and give the ignition 7.4volts, in order to get a stronger spark. This just occurred to me...

Jaketab

My Feedback: (2)

Short stack broke of the collector ring. Tig weld or is it too far gone? Many flights on the old reliable 250.

ChemE

It looks like its time for a new one in my opinion!!!!!

Jaketab

My Feedback: (2)

The welding shop said they could TIG weld for around $80. A new one is $355 USD and is currently on back order.
I will know in about 1 week it the repair is successful. But yes, I new one may have been a better choice.

ChemE

[QUOTE=Jaketab;12803999]The welding shop said they could TIG weld for around $80. A new one is $355 USD and is currently on back order.
I will know in about 1 week it the repair is successful. But yes, I new one may have been a better choice.[/QUOTE

If you look at the failure, it is not the weld that failed but the aluminum. This indicates a weakness in the aluminum after a long time of use. Also remember you have to paint the new aluminum with high temperature paint so it does not oxidize.

Ragz

I notice that the cam followers are of different lengths for intake and exhaust push rods. 24mm and 25.5mm as per specs. Can someone clarify which length goes where? Left one is longer than the right? Totally lost here. I have removed all push rods from my moki 250 and I find not all are 80mm.. 3-4 rods are almost 81mm.. Same for cam followers. Not all 25.5 are identical.. and not all 24mm are really 24.. Is this ok?

Ragz

I am trying to do a compression test on each cylinder on the 250. I have unscrewed all plugs and am screwing the pressure gauge in each cylinder one by one rotating the prop to check the pressure. I find that only cylinder 4 shows 95psi pressure. No other cylinder registers any compression. Does this have to do with all plugs being removed? If so, then why does cylinder 4 only show compression?

I found something peculiar, to me at least, since im not an engine expert. When I remove the push rods from a particular cylinder, it suddenly develops around 50psi pressure. But the moment I install the push rods back in, it doesnt have any compression. But this is not the case with cylinder 4. What the heck is happening. Its obvious im doing this incorrectly.

ChemE

The longer cam follower goes to the prop, the shorter to the crank case. Length may not be 100 percent, but you have adjustment in the rocker arm.