Bendix Mag Rebuild?

I got a flying used engine for my project with Two Bendix mags (S4LN-20 and S4LN-21) that are working fine.

*BUT *

1. Should I go ahead and rebuild them?
2. If so, Who is a good rebuilder?
3. Replace them with Slick mags?
(for now, electronic ignition is not an option)


Dkb

My $.02:

Pull the mags and inspect the impulse couplings per http://www.tcmlink.com/pdf2/MSB645.pdf

If that checks out put them back on, run the engine and if its running fine, don't fix what's not broken. Bendix mags are generally pretty bulletproof. The cam follower and points might need to be adusted and you need the pointer tool to do that.

Mags are simple to work on...if you can build an airplane you can easily work on mags.

Like bob says. You can find the whole manual online. Once you lern the guts you can keep S4's tip top pretty cheap.

Bendix 1200 Mags

In my other world when I was an IA A&P and maintained a 310r 421 Golden Eagle I was the one whom rebuild the mags.

The 421C was pressurized and saw high altitude.

Take care of the mags by the book and all will be well.

Mag comment

I believe a generally held opinion is that Bendix mags are more robust than Slick. A west coast mag shop built me Bendix for my SINGLE magneto A40 antique engine. They advised something I had never heard discussed. If you pull the armature for any reason, it should be stored or shipped in steel mass to retain optimum magnetization. Rocket Bob is probably right about inspecting the primary failure mode. If you overhaul, I can give the contact info for the shop that will turn key O'haul or simply re magnetize the armature. My engine starts first blade hand proping. I am told Bendix is significantly hotter output. larry

Trying to find the digital manual for the SL4N-20

Does anyone have a link for the Bendix Manual....I can find the D version, and the one for converting the impulse Coupling to a Shower of Sparks, but it seems like the most popular Bendix SL4N- 20 and 21 500 hr inspection/overhaul manuals have disappeared from today's search engines.

FYi....was not getting my right mag to show up on the timing box when checking the timing on the mags. Turns out there is small amount of oil getting past the internal oil seal (about 400 hrs on the mag), that would prevent the spark when setting the timing. A friends Cardinal had the same issue after about 300 hrs on his "rebuilt" Bendix mag - anyone know if there was just a seals being made several years ago?

Thanks,
Paul

RV7A