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  #1  
Old 01-29-2020, 10:47 AM
avrojockey's Avatar
avrojockey avrojockey is offline
 
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Location: Appleton, WI
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Default Slick Inspection - Do I Need a New Distributor Block Assembly?

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.



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  #2  
Old 01-29-2020, 12:08 PM
Scott Hersha Scott Hersha is offline
 
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Default

See Champion service bulletin SB1-15A:

https://www.championaerospace.com/as...A_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.
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  #3  
Old 01-29-2020, 12:39 PM
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avrojockey avrojockey is offline
 
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Quote:
Originally Posted by avrojockey View Post
Manual says bearing should be 0.246 +.002/-.001 so I'm checking that next.
Oilite bearings are within limits...on the small side (.245) so they're not worn.
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  #4  
Old 01-29-2020, 12:40 PM
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avrojockey avrojockey is offline
 
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Quote:
Originally Posted by Scott Hersha View Post
See Champion service bulletin SB1-15A:

https://www.championaerospace.com/as...A_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!
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  #5  
Old 01-29-2020, 01:54 PM
OKAV8r OKAV8r is offline
 
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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...
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Old 01-29-2020, 02:34 PM
lr172 lr172 is offline
 
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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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Last edited by lr172 : 01-29-2020 at 02:42 PM.
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  #7  
Old 01-29-2020, 03:07 PM
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rocketbob rocketbob is offline
 
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Almost every one I take apart looks worse.
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  #8  
Old 01-29-2020, 03:15 PM
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avrojockey avrojockey is offline
 
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Quote:
Originally Posted by OKAV8r View Post
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.
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  #9  
Old 01-29-2020, 03:22 PM
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avrojockey avrojockey is offline
 
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Quote:
Originally Posted by lr172 View Post
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.
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  #10  
Old 01-29-2020, 07:09 PM
BH1166 BH1166 is offline
 
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Default 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.
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