DanH

DanH

Legacy Member
Mentor
On the runup pad, the usual 40 drop was more like 100 on one of them. Not rough, not ugly, just excessive. No problem, only going up to screw around anyway, so let's test.

Set up 65% cruise, lean just short of rough. Turn on EFIS logging. Run on one ignition for a bit, then both for a moment, then the other ignition, the one with the abnormal drop. Catch a few barrel rolls, then back to base.

At home, download the memory stick, find the flight segment, dump the single ignition EGTs into Excel and plot them. Look at #4 when running on the top plugs, right side of the plot.

Single Ignition Runs.jpg

Today, back to the airport, pull the cowl and plenum cover. Pop the plug cap off #4, look inside the boot. The little C-shaped spring which clamps the tip of the spark plug was broken, so it had been chaffing and fretting and creating rusty dust, the result being high resistance.

This is a new plug terminal. The spring is the black part.

Ain't science grand? ;)

Plug Terminal and Boot.jpg
 
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Nice!
How long and what would have to happen before that was found on a legacy non-4 cylinder monitoring system? Don’t want to mention how many times the information is there and logged but ignored.
 
DanH said:
On the runup pad, the usual 40 drop was more like 100 on one of them. Not rough, not ugly, just excessive. No problem, only going up to screw around anyway, so let's test.

Set up 65% cruise, lean just short of rough. Turn on EFIS logging. Run on one ignition for a bit, then both for a moment, then the other ignition, the one with the abnormal drop. Catch a few barrel rolls, then back to base.

At home, download the memory stick, find the flight segment, dump the single ignition EGTs into Excel and plot them. Look at #4 when running on the top plugs, right side of the plot.

View attachment 63088

Today, back to the airport, pull the cowl and plenum cover. Pop the plug cap off #4, look inside the boot. The little C-shaped spring which clamps the tip of the spark plug was broken, so it had been chaffing and fretting and creating rusty dust, the result being high resistance.

This is a new plug terminal. The spring is the black part.

Ain't science grand? ;)

View attachment 63089
Click to expand...
Yup. Have had this problem before. Check the clips during annual or if you don’t feel a snap when pushing the lead onto the spark plug

Headsup for spark plug lead issue

Something to be aware of: Twice in the last year I have had to replace one of the leads between my pmags and my automotive sparkplugs. In both cases, the very small band that is attached to the metal retention clip that attaches to the sparkplug tip had broken. This piece is what causes the...
vansairforce.net vansairforce.net
 
erich weaver said:
Yup. Have had this problem before. Check the clips during annual or if you don’t feel a snap when pushing the lead onto the spark plug

Headsup for spark plug lead issue

Something to be aware of: Twice in the last year I have had to replace one of the leads between my pmags and my automotive sparkplugs. In both cases, the very small band that is attached to the metal retention clip that attaches to the sparkplug tip had broken. This piece is what causes the...
vansairforce.net vansairforce.net
Click to expand...

Interesting. The terminal posted above is a leftover from when I built the last spark harness about seven years ago, Bought in bulk from Kingsborne Wire, perhaps not the best quality available. I ordered a package of MSD terminals last night. Note the plated spring. Erich, do you recall if your broken band springs were also black oxide?

MSD Spark Plug Terminal.jpg
 
DanH said:
Interesting. The terminal posted above is a leftover from when I built the last spark harness about seven years ago, Bought in bulk from Kingsborne Wire, perhaps not the best quality available. I ordered a package of MSD terminals last night. Note the plated spring. Erich, do you recall if your broken band springs were also black oxide?

View attachment 63107
Click to expand...
sorry, don’t remember,but I will check in the next couple days when I’m back at the hangar
 
I have caught similar spring breaks twice in my airplane - by listening to the radio. Find a quiet frequency, kill the squelch to listen for the "tick tick tick" of your ignition (if present), check which side it's coming from, and start looking.
 
How do you force that retention clip out of the rubber cap? It wont slide.
Seems that the cap is suck onto the harness lead. Silicone? Thanks.
 
GOFT said:
How do you force that retention clip out of the rubber cap? It wont slide.
Seems that the cap is suck onto the harness lead. Silicone? Thanks.
Click to expand...
Some hand sanitizers work well to lube up these things. Once dry, the rubber sticks quite well.
 
MSD spark plug terminal caps are also made of stainless steel. Helps eliminate corrosion and resistance due to moisture. I also use dielectric grease on the caps during installation.
Good case for High Output Electronic Capacitor Discharge Ignitions.
 
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