The International Cessna^® 170 Association

Just had my Bendix Mags IRAN'd and have been advised I need to replace one of the drive gears. Apparently it is pitted and appears to be delaminating (?) Repair facility has a possible source for a serviceable gear, but owner of that business is out of town until Monday at which time he will let me know if she has one available and at what cost. Anyone know of a good source for one of these gears? This is for a Continental O-300B.

Frank

Disregard my earlier post. Repair facility found a serviceable gear on an extra mag in his shop and will install it prior to shipping later this afternoon.

thanks,

Frank

First of all the gears are heat treated steel and don't delaminate. Delamination is a mode of failure for composite materials. Modes of failure are also known as 'failure mechanisms'. In laminated materials, repeated cyclic stresses, impact, and so on can cause layers to separate, forming a mica -like structure of separate layers.
The real concern is why just one mag had this problem of corrosion and did your mechanic inspect the mating drive gear for corrosion. If your mating gear has corrosion; then you need to determine if the corrosion requires a replacement that will require you to remove the engine and replace the corroded gears. If you ignore this; the corrosion will cause excessive gear tooth match and effect the timing of your magnetos. You may want to learn more by engaging a complainant engine mechanic that is educated to all materials that your engine is made of. Don't be a turn key operator who ends up flying machines they don't understand and become a statistic. Respectfully Andrew ...if I can help please feel free to contact me at airplaneandy@yahoo.com

Thanks Andrew. The comment regarding possible delamination was what my repair facility owner used to describe how the gear appeared. I haven't seen the gear yet (it will be sent to me along with my mags). I agree with your description of what delamination is and am aware of the type of material from which the gears are produced. At this point I have not inspected the accessory case gears that drive the mags, but will do so upon receipt of the mags prior to installation. I have a competent mechanic who will assist in the installation, timing, etc of my inspected, repaired mags.

Frank, May I suggest you have the facility return the defective gear to you? (for your "personal education", of course...and bring it to convention for the seminar.)

Did you notice anything peculiar about the gear when you sent it in? or did your mechanic send it on your behalf?

George, I pulled the mags and shipped them to TX for IRAN. I didn't inspect the drive gears prior to shipment. However if Aaron says there is a potential issue with anything on a mag then that is sufficient expertise for me to replace the item. He sees many, many more mags/drive gears in any given time frame than any of the IA/A&P's at the usual shops. He is sending the questionable gear along with the mags and I will do my best to remember to bring it to St Louis.