1974 M20F Magnetos

[aerobat95]

Quick question I know I have Bendix Mags but does anyone know what type are on a IO360-A1A? Also the 500 hr inspection is that a mandatory requirement? What all is involved? Thanks.

[jetdriven]

Quick question I know I have Bendix Mags but does anyone know what type are on a IO360-A1A? Also the 500 hr inspection is that a mandatory requirement? What all is involved? Thanks.

AFAIK they are Bendix S20 series, and the 500hr inspection is not mandatory per the regs, but is one of the few things that shoud be treated as mandatory.

The 500-hr is basically an OH without replacing the shaft bearings. All components are checked for proper operation, reassembled, and retimed internally with point gap set.

[aerobat95]

So what parts should I be looking to purchase? How much in parts is it? Approximately how many hours are involved per mag?

[N601RX]

Does anyone know the weight difference between a pair of bendix and slick mags? I think I've read it was around 6 pounds for the pair? Did the early IO360-A1A's come with Bendix when new?

[jetdriven]

So what parts should I be looking to purchase? How much in parts is it? Approximately how many hours are involved per mag?

As important as magnetos are and how much they get screwed up, I think the conventional wisdom is to send them off for a ~250$ inspection.

[garytex]

Jetdriven is spot on.

[aerobat95]

So where would I send them off to? My A&P here on the field has rebuilt tons of mags so I trust him. For the ~250 what all do they do?

[jetdriven]

It might be OK to have him OH your mags then, I hear Bendix are easy to do, but it does take special tools. If you mechanic has the experience perhaps thats the best. Bendix are rumored to be pretty robust, so the inspector check everything, replace bad or worn components (such as distributor towers and distributor gears), replace the points and set the E-gap.

I am sending mine to John at hummingbird rotorwing. Call him. Im getting rid of the Slicks for Bendix 1200s.

Quality Aircraft Accessories is good too but rather expensive. They are fast though.

more info.

http://www.eaavideo.org/video.aspx?v=1367499350001

http://www.avweb.com/news/savvyaviator/savvy_aviator_63_recommended_or_required_199001-1.html

http://www.avweb.com/news/savvyaviator/savvy_aviator_43_high_altitude_misfire_194870-1.html

http://www.sacskyranch.com/bendix.htm

[BigTex]

I sent mine off to Select Aircraft Services to have them both IRAN'ed. Don Maxwell sends all of his Mags there. They did a great job and it cost around $600. Their website is www.selectaircraft.com.

[aerobat95]

So they are supposed to be OH at 500 hour intervals then? This 500 hour inspection/OH is kinda confusing. Do Mags just work and then fail all of a sudden or would one notice problems developing over time? Currently mine have very little drop and the drop is very close between the two when tested during the runup.

[garytex]

Oh, I have run mine out to 800 hrs, but the parts showed me that that was plenty long enough. Worn cam followers, toasted points, capacitors looking dodgy. Are you old enough to remember the "tune-up" that was needed on old breaker point vehicles in the 70's and before. Same story. You could go more than 20,000 mi. with no maintenance on that distributor, but it increased the chances that one would sleep out on the ranch, or have a long walk back...I don't want to walk back.

Gary

[jetdriven]

Bendix mags are stone reliable, I think the general opinion is Slicks are less so. (Slicks use a plastic breaker point cam and their QC on components, frankly, sucks). A rash of AD's and the resulting service letters a few years ago on magnetos got everybody on the 500-hr inspection interval frame of mind. I don't think there is a legal requirement anymore for 500-hr inspections on most magnetos, but I treat it like an airworthiness requirement regardless (and I am a big believer in "on condition" maintenance). Especially and absolutely if you run a Bendix dual mag.

From what I have learned, a 500-hr is similar to an OH but the requirement to test and/or remagentize the rotor and to replace the shaft bearings does not apply to the 500-hr inspection.

The fact our replacement Bendix 1200 mags came from an experimental and the history is shady, we are doing a real OH on them. Principally to get away from the Slick reliability and cost per cycle. The cost difference on the Bendix 1200 overhauls is <100$ each anyways. Busch's mags are also Bendix 1200s, and they havent been OH'd in twenty years. They do come off every 500 hours for inspection though. If I were you, and your mechanic knows what he is doing,I would use him. Shadrach (Ross) rebuilt his Bendix mags under supervision of an A&P. Just be sure to have the special tools, and current service manual if you do.

These are my opinions alone, and YMMV.

[aerobat95]

LOL....the "tune-ups" were before my time.....My first car was a '85 Ford Tempo.....but it makes sense. I will see what my A&P says.....annual is just around the corner in Nov.

[BigTex]

I highly recommend sending them out to folks that specialize in mags. If the big guns like Don Maxwell and Mike Busch send their's out instead of rebuilding them in house, there's a reason.

[Lood]

Here in SA, the 500hr/ 5 year exercise is mandatory and it normally costs around $700 - $800. When I had my engine overhauled, I ran a sort of poll and asked many, many pilots whether I should convert to Slick mags and the end result favored Bendix by far. So, I stuck with them.