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Replacing Magneto P-Lead? printer friendly version
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D. Porter
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Posted Sunday, June 10, 2012 @ 11:54 PM  

I'm getting considerable ignition noise on the handheld comm radio in N1700F and started looking for the problem today.

It appears that the P-lead was cut and spliced just forward of where it passes through the firewall. The P-lead is shielded from the mag to the splice, but from the splice to the panel mag switch it is all two-conductor unshielded cable. So I'm guessing that is the source of my noise.

I'm going to make a new P-lead from 4' of 20awg http://www.aircraftspruce.com/catalog/elpages/shieldwire.php.
Question is, can I unscrew the P-lead connector from the magneto housing without tipping the engine down? It looks like it should be possible but just wondering if anyone has actually done this before I try it.

Don

Bob Grimstead
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Posted Tuesday, June 12, 2012 @ 10:41 AM  

Sorry Don,

I haven't tried that, but do beware if you do tip the engine forward/down, that the throttle cable (at the very least) is disconnected from the carburator. If not, you can kink the inner, subsequently making it very difficult to make small throttle adjustments. Although a little time-consuming, it might actually be easier to remove the carburator rather than damaging it or any of its cables.

Yours, Bob

--------------------
Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Donald
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Posted Tuesday, June 12, 2012 @ 12:53 PM  

Don't really know about the RF4, mine is an RF3, but from photos on this site the 4 looks to have the fibreglass bowl through the firewall to house the magneto, just like the 3. IF, if it's the same then yes you can do it by removing the gear 'snail' and that bowl to get access to the back of the magneto. There are 4 small nuts (M7 I think) that hold that bowl to the back of the firewall, but it's a bit of a blind fumble. I've done it with the gear doors held 180degrees open with a bungee chord, lying on my back, head on the main wheel and reaching up and forward with the spanner. The nuts are in the 1:30, 4:30, 7:30 and 10:30 positions.

Whether that's easier than disconnecting the carb and swinging the motor down I have no idea for those swinging mounts are not on the 3.

D. Porter
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Posted Tuesday, June 12, 2012 @ 02:31 PM  

Thanks guys, good info.

I tried a stubby adjustable wrench on the magneto P-lead connector and found I was able to loosen it just enough to remove it by hand. That still left a ground wire connected to a terminal under a rear mag cover screw, which I couldn't access but did cut. I will temporarily relocate that ground wire to elsewhere on the mag housing until I get access to the rear of the mag someday. Should have the new P-lead wire tomorrow so hope I can reverse the process without problems. And I really hope this fixes the RFI problem.

Also, the P-lead and plug wires are secured to the magneto by large nylon cable ties, about 20" x 0.3". Those don't seem to be commonly available but I found them at McMaster-Carr.

Don

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