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Discussion Starter #1
So, was taking apart my MKIII spare starter to rebuild it, clean it ect...

I noticed these arcing marks between the end cover and brush holder.

Everything on the field frame, brushes, meters out correctly with continuity and no continuity where applicable.

I can't seem to understand why these arcing marks are present. The negative side brushes have continuity to this back plate which is then bolted to the end cover which is grounded to chassis.


any thoughts on what caused this, and more importantly is this a reason not to rebuild it?

thanks
rick



 

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Discussion Starter #2 (Edited)
ok.. after some closer inspection and thought, I'll take a stab at answering my own question.


In a "clean and new" situation, the negative brushes have a path to ground through the back plate, then through the screws that hold the end cover on to the back plate. Over time, buildup of dust/moisture, etc.. caused resistance to originate between the two screws and the back cover, as well as, the physical contact point of the back plate and end cover (where the arc marks are). Eventually this resistance build up enough that arcing occurred directly from the back plate to the end cover.

Although my camera will not take a close up of the two screws, I can see (with my magnifying hood) that some of the threads on the screws show signs of arcing as well.

That's my best theory, and as long as I clean up these contact areas of the plate and cover and perhaps use 2 new screws then a proper path to ground will be established, and no arcing will occur. (at least until buildup of dust/corrosion occurs again)


rick
 

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Rick, a bit like spot welding: high current in a small surface. The crank Amps is nowhere near spot welding, but still high. Enough to, in the long run, do local pitting on the surfaces.
 

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Discussion Starter #4
yeah, makes sense.

I ground off the pitted areas with my dremel on both the plate and the cover, however there was so much material that was pitting and then removed when I put the dremel to it, that there was a gap between the cover and back plate at those areas. I took two .5 mm thick small washers and used them between the plate and cover to fill up the gap. Cleaned up the screws and threads in the cover and plate, and it now fits together snug.

I'm now just waiting for a new plunder and plunger contacts for the solenoid and then give it a test crank (off the car of course).
 

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I'd use a dab of either aluminum or copper antiseize compound between those new parts. The metal in the compound improves conductivity, and grease seals out moisture.
 

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Discussion Starter #6
I'd use a dab of either aluminum or copper antiseize compound between those new parts. The metal in the compound improves conductivity, and grease seals out moisture.
Ah yes, good idea, I have some copper anti-seize that I used on an old Subaru's OX sensor.

will do,
thanks
rick
 

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I like "Jet Lube SS30", it's copper-based, and thick enough that it stays put. I use it on antennas, but it works great as a general purpose antiseize, too.
 

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IF Doc uses it I'm ALL IN!!

I like "Jet Lube SS30", it's copper-based, and thick enough that it stays put. I use it on antennas, but it works great as a general purpose antiseize, too.
 
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