Gold Lifetime Member
Join Date: Jun 2009
Location: Tomball TX, DeRidder LA
Re: rivnuts in frame for ground
You are proposing the following scenario: You are joining a steel frame that has an aluminum rivnut, using an electrical lug that is made of nickel plated copper. All of this is fastened with a stainless steel bolt or a zinc plated steel bolt. This connection will be exposed to the elements.
There are a lot of dissimilar metals in contact with each other. Galvanic corrosion is likely to occur. I know if you use the stainless bolt and run over a mud puddle, the aluminum will corrode. The zinc plating on the steel bolt will eventually go away and the bolt will rust. Trying to remove that rusted bolt will cause the rivnut to spin. Your idea of a steel rivnut will eliminate one of the dissimilar metals.
Counter sinking the rivnut is a great idea. Think about how the rivnut collapses. The rivnut comes in contact with the subframe in very small areas. This is not a good electrical connection. Flush mounting the rivnut will allow the lug to directly contact the steel subframe therefore providing more surface area for the electrical connection.
On my car, I welded a little 3/8" thick tab to the subframe. I drilled and tapped a hole in the tab. I used a zinc plated steel bolt, lock washer, flat washer to hold the lug to the frame. I coated the electrical connection with Penetrox to prevent electrical corrosion. I originally thought about using a silicon bronze bolt. This was not one of my better ideas. It would have been the sacrificial element if galvanic corrosion occurs.
Look for a spot on your subframe where you have access to both sides of the frame. Use a bolt and nut for the connection.
A star washer cuts through the paint. It scratches the surface as it is tightened. I would not use one for a high current application since the electrical contact is on the tips of the star.
Money can't buy you happiness but it can buy you car parts which is bout the same thang.