Primarily for general aviation discussion, but other aviation topics are also welcome.
#1519049
Thats it really,
Are they stripped down re wound, bearing changed, brushes changed, springs re sprung, diodes lubricated( Im showing my ignorance here as I don't believe diodes are involved) or is it just a bench check and a paperwork exercise ?
£1000 every 500 hrs (if lucky) hours seems a bit steep to me.

A few years back we had a recently O/H one play up and I'm might be wrong but from memory the guarantee was only 3 months.

I did a search and couldn't find an answer so apologies if previously answered.

Cheers J
#1519070
Points, bearings, capacitor being replaced. Gears checked for wear and replaced if needed, P gap re-adjusted, cap checked for cracks and contacts being checked for wear. Clean, lubricate and have a shiny new paint. Have I forgotten something?
#1519117
Magnetos do not require overhauling every 500 hours.

It is a myth.

A Service Bulletin came out years ago suggesting an inspection at 500 hours but it was nothing more than that. All the mags I have had, had a similar service life as the engine - 2000 hours.

If it ain't broke, if it is still working - leave it alone :mrgreen:
#1519211
If it ain't broke, if it is still working - leave it alone 


Not quite! Old, lacquer-potted windings are susceptible to cracking, damp-ingress and eventual breakdown....but unusual in anything under 30 years old .
Modern Epoxy-potting is "fit and forget "
A hypodermic syringe can be used to lubricate ballraces NOTE 1/3 full MAX.
Sliprings usually have a brass contact-pad and sometimes this wears at a different rate to the rest of the (plastic) ring. Skimming the surface to remove any step will lengthen the life of the contact-brush, which will, in turn, reduce carbon-dust and the possibility of tracking and shorting.

POINTS ! they wear, the "heel" that rides the cam wears. Normally, there's a grease-soaked pad that should lubricate the cam........it takes a "set" sometimes it's possible to turn it over and then the bend actually improves the pressure.

The points themselves are normally a tungsten facing on a small post.....one will ALWAYS build a lump, the other a crater (DC current,tiny spark every time they open, think arc-welder)
Polish with a whetstone / wet and dry paper (600 grit is OK) a magneto/Swiss/Warding file may be needed first , to reduce the "pip" .

The "gap" is absolutely critical for optimum performance, as it determines at what point in the armature's rotation, the optimum flux-collapse occurs. The timing of the magnetic "break " is part and parcel of this.


I suspect a lot of Mag troubles are caused by poor points-maintenance.

Lastly, the capacitor...they're cheap, they quench the spark at the points, thus lengthening their life and preserving timing. The quenching also ensures a much quicker collapse of the primary-winding current. - this, in turn, gives a stronger induction into the secondary-winding = a fatter spark!

There's plenty of info "on the net" for those seriously interested.

by and large this "dump or overhaul " business, strikes me as a total con-trick.

Bead-blasting and painting are purely cosmetic. the major issues are points and bearings...they're the wearing bits.

If dismantling, be aware some designs have paper insulators around the armature- bearings. they must be in place and intact!

hth.
#1519289
Despite having an old Crypton, with a proper 'scope, I never tried it....I was able to pick the pulses off an early Bosch ECU, fitted to a V-8 Merc.....it was only firing on 4, ....replaced the huge cast-alloy box in the side of the passenger footwell.....and it started on all 8.....owner never had any more problems...odd!
forgot to say, you can mark a mag as appropriate, and use a strobe to set the points. (pick up HT trigger pulse as usual, use a separate to power the light..... still have a dwell-meter and a timing light!.
#1519511
Trent772 wrote:Magnetos do not require overhauling every 500 hours.

It is a myth.

A Service Bulletin came out years ago suggesting an inspection at 500 hours but it was nothing more than that. All the mags I have had, had a similar service life as the engine - 2000 hours.

If it ain't broke, if it is still working - leave it alone :mrgreen:


Am not sure. I think that the Slick has to be done every 500h, the Bendix are 'recommended'.

Edit:
Made more digging and found that there is a SB on the Slicks while Bendix recommends. The Slicks were/are known to go downhill fast around the 500h mark to the point that in some cases it is cheaper to buy new.