Interesting EGT.....
 

I've been doing some work on teh Valkyrie, and had a funny signature a few minutes after take-off the other day. The airplane runs dual P-Mags and auto plugs - very smooth, easy to get LOP, even though it is carbed. I still have what I consider to be the best display of EGT's on any of the EFISes - GRT's plots of EGT versus time (I used to love reading strip chart recorders too .... dating myself!).

So shortly after take-off, I leaned to peak, and as I did this, all four EGT's came together nicely, as they always do. LOP, all was smooth and CHT's started coming down. Then all of a sudden, a few misses - a touch of roughness. I looked down, and EGT #2 had jumped up and out of the pack by almost100 degrees! I had to riches things up to smooth it out, and that meant I was now ROP, and had to go a long ways rich to bring the CHT's down. Teh errant EGT rejoined the pack, but not completely.


I had removesd intake tubes as part of my maintenance work, so immediately suspected a leak - but why it would start inflight was a mystery. The mystery cleared when I took the cowl off and looked at cylinder #2 - the lower plug wire had popped off! The P-Mag automotive plug wires have to be "burped" to make sure you get the air out, and that the metal cap has clicked on to the plug.

Easy to fix - and the EFIS made it easy to know where to look!

Paul, I know you've talked about burping the plug caps before. I think you should have a serious talk with your mechanic :).

As I read your story, the very first thing that came to mind was that you lost a plug.

If you really want an eye-opener, do a mag check at altitude while 50 LOP. Even with all the spark advance of the EI, one plug just can't get everything burned.

Unlikely an induction leak would go to higher EGT if you are LOP - it would go leaner still and get cold. That would explain a miss though. So the EGT trend on the strip chart is the key discriminator.

I'd like to see you change a paper roll in flight, though, or what you do with all that chart paper piling up in the floor of the -8. I suppose you could have a take-up roll on the outfeed. ;)

Yup - spent a little quality time after this with a set of long needle-nose pliers persuading the contacts to grip the plug tightly.

I wonder if there might be a spring clamp just the right size to fit over the boot?

Like those spring clamps you see on modern cars for hose clamps. It would need to have just the right size/clamp pressure to provide more positive retainment, but not chafe/cut the boot. And the clamp ears would have to be short enough not to get too close to the cylinder head fins, etc.

Burping Plug Caps?
 

Sounds like you're running Rotax plug caps!

I got a good suggestion off--line from a long-time experimenter who uses just a touch of Dow #4 on the inside of the boot - slides right on, and makes for a nice click without any doubt. Great suggestion. I've ben using the P-mags and their plug wires for six years now - never had one come off in flight - so not a big deal. Just annoying!

Paul

If you pull off the rubber boot and look at the metal cap that makes the contact with the plug you can see a small circular clip that's job is to provide the tight fitting, snap-into-place connection. I have had two of those little clips break at different times, resulting in intermittent connection or no connection at all. Just another thing to be aware of and check. After the second one I replaced all the leads.

Erich

Paul, I might have been a bit hesitant to use an "insulating compound" such as Dow 4 on plug connectors but if you go to this technical blurb from Dow Corning you can see that it is in fact recommended for spark plug connectors.
http://www.dowcorning.com/content/ne...4_Compound.asp

If you use the right amount of dielectric grease (which I think is what Dow #4 is) and you get the clicker clicked and you burp the cap, these things are almost hard to remove. I can't imagine they would come off in flight if all 3 are true.