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Slick Inspection - Do I Need a New Distributor Block Assembly?

avrojockey

Well Known Member
Patron
I'm upgrading one mag to a P-mag and need to swap the tach pickup to the left mag. Since the plug was hard to get too I decided to remove the mag and do a 500-hr inspection IAW L-1367F.

All looked good but there is obvious contact happening between the electrode towers and the electrode finger on the distributor gear. The electrode finger on the distributor gear is not loose and there's no signs of cracking in the gear. Also, there's no cracking in the distributor block. There is, however, some slight play in the gear when assembled in the distributor block, which leads me to believe the olite bearings are worn.

Does anyone know if contact between the gear electrode and the distributor towers is cause for replacement? The overhaul manual is vague...
"Inspect the brass electrode posts for signs of physical wear. Replace block assembly as necessary."

Manual says bearing should be 0.246 +.002/-.001 so I'm checking that next.

IMG_0928.jpeg

IMG_0929.jpeg

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See Champion service bulletin SB1-15A:

https://www.championaerospace.com/assets/technical/SB1-15A_20181112.pdf

The distributor gear shown in your picture has a copper electrode and is called out in the sb for removal. It should be replaced with the new design that has a monel electrode. I know we don?t have to comply with service bulletins, but you are anyway with the 500 hour inspection. You can purchase the new one from aircraft spruce for 113.75. Champion will reimburse you the cost of the part, but the return has to be handled by the distributor - aircraft spruce - so talk to their service department and reference the Sb.
 
See Champion service bulletin SB1-15A:

https://www.championaerospace.com/assets/technical/SB1-15A_20181112.pdf

The distributor gear shown in your picture has a copper electrode and is called out in the sb for removal. It should be replaced with the new design that has a monel electrode. I know we don?t have to comply with service bulletins, but you are anyway with the 500 hour inspection. You can purchase the new one from aircraft spruce for 113.75. Champion will reimburse you the cost of the part, but the return has to be handled by the distributor - aircraft spruce - so talk to their service department and reference the Sb.

Thanks Scott!
 
One of the alignment holes in the distributor block looks stressed, like the mag was rotated with the timing pin in place. Suggest you look closely at the rotor shaft below the rotor gear, where the cam rests in the slot of the shaft. Look closely for cracks at the base of the slot, using minimum 10X magnification...
 
measure the shaft on the cap. Looks very worn. Something must be loose, as you can see a groove worn in the side of the main tower walls. Top of the shaft looks very worn, indicating excess slop somewhere, allowing it to pivot and wear at the top. Also, make sure you take an ID measurement down low in the bushing. It looks more worn down there and would allow the pivotting that appears to be causing damage.

For busihings in an application where only one side of a rotating shaft is suppoted, multiple measurements down the length of the bushing are required. Also, you need to take measurments in numerous radial directions. Your wear appears to be an out of round issue. Some directions can show true and others highly worn. Bushings in this application can wear very differently than those where both ends of the shaft are supported.

Larry
 
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One of the alignment holes in the distributor block looks stressed, like the mag was rotated with the timing pin in place. Suggest you look closely at the rotor shaft below the rotor gear, where the cam rests in the slot of the shaft. Look closely for cracks at the base of the slot, using minimum 10X magnification...

I noticed that too but the hole is not damaged, nor is the hole damaged in the distributor gear.

Ill take a look at rotor gear and rotor shaft.
 
measure the shaft on the cap. Looks very worn. Something must be loose, as you can see a groove worn in the side of the main tower walls. Top of the shaft looks very worn, indicating excess slop somewhere, allowing it to pivot and wear at the top. Also, make sure you take an ID measurement down low in the bushing. It looks more worn down there and would allow the pivotting that appears to be causing damage.

For busihings in an application where only one side of a rotating shaft is suppoted, multiple measurements down the length of the bushing are required. Also, you need to take measurments in numerous radial directions. Your wear appears to be an out of round issue. Some directions can show true and others highly worn. Bushings in this application can wear very differently than those where both ends of the shaft are supported.

Larry

Checked for out of round...all within .0005. Of course this is with my Harbor Freight calipers.
 
Wear marks

How many how?s total on mag in pics? New slicks are recommended to have IRAN after first 500 hours and overhaul after 1000. I am about to conform to SB 15A and do IRAN at 400 since new. Good luck with your repairs.
 
I think it makes a difference on type of use. My mags only had 294 hours on them since new from Lycoming, but new was 2005. There obviously was times of little use and much downtime. Both of my mags needed a complete overhaul on inspection - 725.00 in parts plus labor. Might as well just buy a new mag. I don’t think you can plan on a Slick mag making it to the TBO of your engine. A Bendix mag, maybe, but Slick mags are just not robust enough to last that long. I fly my airplane frequently and I plan on having a replacement plan set up when 500, or fewer, hours rolls around. I have one SureFly right now, and may go with a second one if this first one is reliable.

When we took my mags apart, it was surprising to see the amount of wear that happened in such a short time, and again, a lot of that has to do with lack of use. I purchased a mag from a friend that had an almost new one and had the 500 hour inspection performed on that one, but I don’t expect it to last forever.

Note: When you buy a new mag, they will charge you $250 more if you don’t have a ‘core’ to send to them. I asked my accessories mechanic what they do with those cores. He said they just throw them away because they want to get it out of the system. Goes to show you how long they think they will last.

Incidentally, if you need to buy a new mag, and you don’t have a core to send them, let me know. A core will save you $250. I’ll sell you a core for $100........ um, plus shipping......
 
Not worth the risk

I would fail the block assembly due to the possible FOD contamination on the cracked timming hole, it is not worth messing with. If it breaks off it could damage the gears or it could just find a corner of the mag and never move....but its not worth the gamble in my opinion. Kelly aerospace sells distributor block assemblies for most slick mags now at a lesser cost than the slick counter part. They are available thru aircraft spruce. In the past when doing a 500hr inspection I usually just assume I will be needing to replace the points and distributor block assembly. The most common dist block assembly part number will be ES3822 (not a guarantee as I don't know the model of your mag.)

Mitch AP/IA
 
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