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Question: Coil mounting on QJ 26 CC engine

Started by Erez, July 03, 2018, 14:48:10 pm

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I have been building and flying RC planes over 40 years but this is my first venture into petrol engines.

I apologize if my question seems basic or over-thinking an issue, but here goes:

I got a new QJ 26cc engine (a Zenoah 26 cc clone) but have not installed or run it yet.
Right out of the box I noticed the HT lead from the coil to the plug, was routed under and aft of the carb in a manner in which the HT lead not only had a very sharp bend right out of the coil, but it was also pressing hard against the carb mount and one of the carb mounting bolt's head (see first pic, taken after I removed the coil).

To my eyes this did not seem right and actually the HT lead already had a tiny mark on it in that area and for the above reasons.

Thinking this would not last long, with engine vibration and heat, I removed the coil and mounted it rotated 180 deg from the original position (which is the only other alternative position and orientation to mount it).

Now the HT lead does not contact anything but does have a sharp bend (though less than before).
I also placed some protective plastic spiral shield on the HT lead opposite the carb, for in case it gets pushed back by the airstream and occasionally contacts the carb body.
See pics of how it looks now.

I have no one to consult with on this at our field (all electrics...), and so would greatly appreciate any comments on whether it's OK to do what I've done, or should I have left it alone?
Should I arrange for some support for the HT lead so it doesn't vibrate under wind and engine vibration?


With the Zenoahs, its usually no problem. Just make sure the lead is not touching a cowl.


I would have turned the coil around, I don't like the look of the HT cable bend,,,  :-\
Mode 2 THE only way to fly


July 03, 2018, 15:30:49 pm #3 Last Edit: July 03, 2018, 15:33:19 pm by Erez
Quote from: paulinfrance on July 03, 2018, 15:22:22 pm
I would have turned the coil around, I don't like the look of the HT cable bend,,,  :-\

Before I turned it, there was a sharp corner...and it was pressing hard against the engine.
At least now there's a radius...and no contact with the engine.

Maybe a different coil?


Not familiar with the engine, but what is the tapped hole behind the coil (underneath the connector on the black lead in the second picture) for? Could the coil bolt horizontally - ie undo the upper screw, rotate the coil around and refit that screw into the other hole?

Failing that you could always mount the coil away from the engine, of course.

There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...


This is how the Z26 is done. [attachimg=1] turn it round and reduce the lead length


Quote from: itsme on July 03, 2018, 16:02:46 pm
This is how the Z26 is done. [attachimg=1] turn it round and reduce the lead length

Yes, that's the Zenoah way, but my coil cannot be mounted that way because my coil is a mirror image of the Zenoa coil.
The mounting lugs are NOT centered on the thickness of the coil, that's why I had to rotate top-to-bottom and cannot rotate it right-to-left to be like the Zenoah one.

The tapped hole is too close for that, to the bottom hole. It is intended for when using a boat-mount for this engine, in its marine version.

Interesting idea re mounting the coil off engine.
Hadn't thought of that. I plan using it on a Flair Fokker DR-I that certainly has enough space for that on the firewall.
A question though - I notice that one (the bottom one only) lug of the coil has exposed metal so when mounted it is grounded to the engine body via that bolt, hence I conclude that if I mount the coil off-engine, I just need to ground that lug via a wire, to the engine body?


Yes, exactly. You could even fit an engine kill switch in there. If it anything like the Zenoah, my Triplane was well powered by it. I reckon the 26 has almost the power of the Z38.