Light Aircraft Association

I'm looking to change the HT leads and plug caps on the 1834 VW in my Veep (SR4 mags).

Searching deep into my memory banks as to the type of leads and plugs that were on the VWs in my Luton Minor and previous Veep, I seem to recall hard plastic leads and suppressed plug caps.

Does anyone have any particular thoughts on the softer more flexible (silicone) leads as opposed to the hard plastic type and suppressed or unsuppressed ignition.

I prefer suppressed ignition purely and simply because I like to hear speech in my headphones but what if any effects do the capacitors have on spark performance and what potential is there for the capacitors to shorten the life of the components in the mags?

NGK have a website with some useful knowledge on it. http://www.ngk.co.uk/

http://www.ngksparkplugs.com/techinfo/s ... country=US

For what it is worth.....

.....I was always told that you want approx 5000 ohms between the mag/coil and the tip of the plug. Several ways to do that.
1: Resistive plug eg BPR6ES instead of BP6ES on the old cars.
2: Resistive caps marked 5Kohm
3: 5Kohm-per-foot approx carbon cored ignition cable.

Number 1 is easy to deal with. Just buy the right plug. Number 2 is the same. Number 3 needs you to have similar lengths of lead to get similar resistances. If the resistance is too low then the spark waddles over the sparkplug points instead of blasting over (or summat like that)

Not sure how mags affect the issues. I use NGK caps which are waterproof and have rubber seals at each end.

IIRC, the plug gap on the Leburg system is about 40 thou, on the Morris Minor about 25 thou and on magneto engines the gap is even less due to the lower ability to fire across a gap. Maybe 5kohms is going to be too much. Maybe someone has a lycoming or Continental handbook or training manual?

have a feeling that for the SR4 magnetos you should use 1000 Ohm resistor caps. Brain fade is preventing me from finding out any references and the caps on my Veep 1834 engine are not marked as far as I can see

Interesting. I have 5k resistance plug caps on my VW1600 with SR4 mags. Do you think this could be reducing the spark at the plug?

Cheers

Gary

Quite possible that at low rpm it will not fire with the same vigour. Back-to-back might be the only way to prove it.

Slick mags say 5000 ohms is too much.
http://64.82.22.158/id18.html


http://www.archive.org/stream/aeroengin ... 00pollrich
Useful archive material is some of these older books. Might help?

http://basementbags.com/dhs/magneto-ignition-system.pdf

Slick mag and lead info here, too.


Also, Rotax 655 manual says 0.8 to 1.4 K-ohms