Improper main battery earth point
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100% chingon
Joined: Oct 2005
Posts: 1,003
Improper main battery earth point
If other Max's are the same as mine, I'm not surprised people buy grounding kits for them. Today I had the whole of the air filter box out, allowing me to see where and how the battery was grounded to the body. I discovered that mine was improperly grounded.
The bottom part of the air box is held down by three bolts, each of which passes through a rubber bushing to allow some flexibility.
Standing on the driver's side of the car, if you look at the 'engine side' of the air box (to see, you need the top cover off and the air filter out) the bolt on the left, near the battery, had been used in my car to hold the main earthing lug. (US readers please substitute 'ground' for 'earth')
This is crap because
(1) it is very bad electrical practice to fix any electrical connection with a bolt or stud that has any kind of pressure-flexible arrangement - like the rubber washers in the airbox.
(2) that location wasn't designed for an earth lug and was painted metal.
The correct location for the earth lug is approx. 1/2" to the left of that airbox mounting hole, but it was pretty obvious that the paint had never been removed from around that stud hole.
So I used emery paper to remove the paint from around the hole, cleaned it with carb cleaner, used a spare 10mm bolt to secure the earth lug, painted over it and then reinstalled the air box. (You cannot get to the 'proper' stud hole unless you remove the air box).
Recall that the starting current is in the region of 200A. That connection needs to be tight and clean!
The bottom part of the air box is held down by three bolts, each of which passes through a rubber bushing to allow some flexibility.
Standing on the driver's side of the car, if you look at the 'engine side' of the air box (to see, you need the top cover off and the air filter out) the bolt on the left, near the battery, had been used in my car to hold the main earthing lug. (US readers please substitute 'ground' for 'earth')
This is crap because
(1) it is very bad electrical practice to fix any electrical connection with a bolt or stud that has any kind of pressure-flexible arrangement - like the rubber washers in the airbox.
(2) that location wasn't designed for an earth lug and was painted metal.
The correct location for the earth lug is approx. 1/2" to the left of that airbox mounting hole, but it was pretty obvious that the paint had never been removed from around that stud hole.
So I used emery paper to remove the paint from around the hole, cleaned it with carb cleaner, used a spare 10mm bolt to secure the earth lug, painted over it and then reinstalled the air box. (You cannot get to the 'proper' stud hole unless you remove the air box).
Recall that the starting current is in the region of 200A. That connection needs to be tight and clean!
1) The 200A starting current should never flow through the frame. The grounding cable does run a big dedicated line to the starter.
2) Somebody definitely had that ground point in the wrong place. Like you said, it should be in the tapped hole a little further forward on that flat shelf that the battery tray bolts into.
3) I don't think the emery cloth is too critical - the threads of the fastener usually serve to wipe clean and make good electrical contact. In case you're concerned about it, a simple resistance check from the bolt head to another ground should verify it.
Dave
2) Somebody definitely had that ground point in the wrong place. Like you said, it should be in the tapped hole a little further forward on that flat shelf that the battery tray bolts into.
3) I don't think the emery cloth is too critical - the threads of the fastener usually serve to wipe clean and make good electrical contact. In case you're concerned about it, a simple resistance check from the bolt head to another ground should verify it.
Dave
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