Lucas SR4 Mags - Suppression or not!

rogcal · Post by **rogcal** » Mon Mar 16, 2009 11:38 am

The 1834 VW mounted in my Veep is equipped with non-impluse SR4 mags and it appears that the leads and plug caps are of the unsuppresed type.

I was intending to replace the ignition system with the Leburg modification however, with the recent tragic demise of David Mickleburg, the manufacurer of that mod, there is little chance of my being able to go down that particular route.

The only other option is to improve the current installation by renewing leads, plugs and plug caps plus checking the mags for correct gaps, coil efficiency, leakage, etc.

My major concern is, do I suppress the system or not and if I do would the increase in resistance cause damage to the mags in any way .i.e. premature failure of windings in the coil.

The interference heard on my handheld radio could be dealt with in various ways (I've read the earlier postings on VW ignition noise) but a good starting point would be suppressed caps and or leads.

Does anyone have any thoughts on whether or not suppression by increased resistance is a bad thing or not when it comes to SR4 magneto efficiency and more importantly, longevity.

cardiffrob · Post by **cardiffrob** » Sat Mar 21, 2009 9:07 am

The 'Tank engine' Morris 8 motor used as a donkey gen in the Canturion had supressed plugs and leads. A call to the Bovington Tank Museum in Dorset might secure a few sets of plugs shaped like the standard Lycoming/Continental ones in the same heat rating as the B6HS used as standard on the VW. They are also dismantleable for cleaning! You'd need longer shielding on the leads but a dead set of Lycoming leads would supply that if you inserted a new inner.

rogcal · Post by **rogcal** » Sat Mar 21, 2009 9:16 am

Hi Rob.

It's not the problem of getting hold of suppressed leads (shielded or otherwise), caps and plugs, I can source those very easily, what concerns me is how they affect the spark output and the long term effect on the magneto coil, points and condenser.

Thanks for the response anyway.

cardiffrob · Post by **cardiffrob** » Sat Mar 21, 2009 3:49 pm

http://www.sacskyranch.com/eng174.htm ...has some minor info. Also, the following crowd might be able to answer some questions over the phone? http://www.magnetorepairs.com/tip1.shtml

I don't know anyone else who specialises in Mags other than the 'replace with new' type suppliers.

Rod1 · Post by **Rod1** » Tue Mar 24, 2009 10:57 am

I tried this on a Nipper some years ago. I could get the engine working but the radio not or the radio working (by suppressing the ignition) and the engine misfiring. After a lot of messing about and help from “experts” I resorted to only transmitting with the throttle closed…

Rod1

rogcal · Post by **rogcal** » Tue Mar 24, 2009 11:12 am

I resorted to only transmitting with the throttle closed…

I always thought gliders were non-radio?

Seriously though, has anyone resorted to using a mobile phone (through the headset with an adaptor) instead of a radio where interference has been a major problem? OK not ideal when wanting to work ATC but perhaps an alternative to a radio when visiting smaller airfields which only have a/g!

Would the frequency used by the mobile phone networks be less prone to electomagnetic interference or am I clutching at straws here?

Gary Hancox · Post by **Gary Hancox** » Tue Mar 24, 2009 9:05 pm

Roger

I am experiencing exactly the same problem as you, and am also wondering about the pros and cons of supressed ignition. I am running a 1600 VW which when it came to me was running with carbon core supressed HT leads with, I assume, supressed plug caps as well. (As used on many car engines.) The engine ran well, and I had NO interference on my ICOM radio with the ANL switched on and the squelch turned up.

Whilst doing some mainetnance it was pointed out to me that I should be using copper core HT leads, as the carbon core leads could break down over time. I followed this advice using supressed plug caps (5k) and unfortunately developed (as expected) interference on the radio. At the moment I am using non-suppressed plug caps, and as you can imagine the interference on the radio is very bad.

My thoughts are now that I should go back to using the carbon core HT leads and suppressed plug caps (but this time only 1k resistance), this being on the basis that it worked before with little or no radio interference. Perhaps I could then check / replace the carbon HT leads periodically if they show any signs of breaking down.

However, I too would love to know if by using this set up I could be causing long-term damage to the magnetos.

Cheers

Gary

rogcal · Post by **rogcal** » Wed Mar 25, 2009 10:38 am

Gary. After reading the Sacramento Skyranch article on the link posted by CardiffBob, the theory espoused in it makes a lot of sense i.e. squeeze the oulet and whatever is pumping the fluid or in this case energy, has to work harder and by default more heat.

My VW powered Luton Minor never gave any problems with radio interference however, when I bought it the leads and plug caps were surpressed. When I started having problems with statrting and had discounted fuel problems as the cause, my attention turned to the ignition system and I replaced plugs, caps and leads like for like and still no joy.

When I turned my attention to the magnetos which up until then I had just serviced in the normal manner i.e. points and condenser, I discovered several spark tracks on the inside of the magneto caps and both coils looking as though they had spent a couple of hours in an oven.

Needless to say, I didn't know what I do now and gave everying a good clean up and took the trouble to respray the inside of the caps in an attempt to stop energy pulses going to ground via that route (I knew to do that much) and hey presto the engine fired up and starting became less of a problem. I got rid of the Luton a month or so later, so didn't find out if the problem returned.

It looks as though I shall be rebuilding both mags, shielding the ignition, connecting everying to a common ground (including radio aerial base plate) and keeping my fingers crossed, unless of course someone takes over the production and distribution of the Leburg system but that may never happen and I want to go flying again this decade.