Mag Mystery

[flyingriki]

Have a Slick mag on one side of an O-320. EI on the other side. Mag has about
600 hours since new and never removed for inspection yet. Plugs were new a
couple hundred hours ago. They were cleaned and gapped under 100 hours ago.
RPM drop at 1800 RPM runup is only about 60 RPM.

Problem: Lately the engine almost won't run on the mag alone at low RPM and if
low enough will just die. Of course it runs fine on the EI at low RPM. And
runs fine with the mag at high RPM.

Any suggestions? Pulling the mag is my next step but grounds me for as long as
it takes to have it sent off and repaired if necessary. Just wondering about
any other ideas. Wish I had the tools to do it myself. The Service Pro, Joe Logie, from
Champion went over a spare I have (no impulse for it) in about 15 minutes at
OSH.....

Timing has not been checked yet.

[nrpetersen]

Probably just bad points. You could get by with just replacing them if yr aircraft is non-certified.

[Tom Downey]

The Service Pro, Joe Logie, from

Champion went over a spare I have (no impulse for it) in about 15 minutes at
OSH.....

swap the impulse coupling from the one on the engine, 1 cotter key, 1 nut, and pull it.

[flyingriki]

swap the impulse coupling from the one on the engine, 1 cotter key, 1 nut, and pull it.

Different part number. Not worth the risk without confirmation that it is compatible. Champion say no and the engine is too valuable to play around in the acc. case...

Guess Mike was just waiting for me to watch the webinar...... will pull it and get it IRANed this week Mike!

[Tom Downey]

Different part number. Not worth the risk without confirmation that it is compatible. Champion say no and the engine is too valuable to play around in the acc. case...

Guess Mike was just waiting for me to watch the webinar...... will pull it and get it IRANed this week Mike!

Which part number? mag or impulse coupling?

[invntr]

Once the engine is running the impulse coupling is no longer effective, it's only for increasing the starting spark. Fly-weights inside the coupling are forced outward by centrifugal force thus taking the spring action of the coupling out of the system. Slicks are bad about the plastic cam for the points wearing down and decreasing the point opening gap. I've also seen the electrode inside the plastic distributor gear come loose several times and cause the timing to be all over the place. 600hrs is a long time for a Slick mag without inspection. I believe a 500 hrs O/H interval is recommended. Ck your timing with the new Rite-System Kit if you want it to be digitally accurate.

[SteveC]

Mike Busch is really adamant about getting mags IRAN d every 500 hrs. He also stresses sending them to a specialist rather than your friendly mechanic, as there are a number of special tools required not usually present in most A&P's shops.......

[skywagon]

Mag problems at low RPM's is usually caused by the point gap closing to a bare minimum. This is caused by the fiber points bar on the points that follow the distributor cam action. If the cam gets dry, dirty, etc. it will wear down the rubbing bar. The results are the slow closure of the points gap. At high RM's this closure is less noticible due to other forces working on the points and electrical spark generating system. However, that RPM range will soon have problems also.
Rule of thumb....check the mag points and gap at every 50 -100 hrs. After the points are checked or re-set, the timing should be checked too......

[Tom Downey]

Mag problems at low RPM's is usually caused by the point gap closing to a bare minimum. This is caused by the fiber points bar on the points that follow the distributor cam action. If the cam gets dry, dirty, etc. it will wear down the rubbing bar. The results are the slow closure of the points gap. At high RM's this closure is less noticible due to other forces working on the points and electrical spark generating system. However, that RPM range will soon have problems also.
Rule of thumb....check the mag points and gap at every 50 -100 hrs. After the points are checked or re-set, the timing should be checked too......

The wearing of the cam, or the cam follower will cause the points to open late, and close early, which changes the dwell of the coil induction and results in a weak spark. and of course a large mag drop.

[Mike Switzer]

For an experimental, I'd recommend taking the mag to your local tractor dealer, if they have a mechanic over 40 that knows what it is...

Not that I ever get mine serviced, I've got an Allis Chalmers WD45, a Case SC & a Farmall M, all with mags real similar (or the same) to the ones on our "modern" planes, I never have to do anything to them. I've been mowing with the M for over 10 years with no service to the mags other than a few drops of 3 in one oil in the cups every now & then...