Nissan grommets and bushings
C&R Racing delivered my custom heat exchangers this week. Before mounting them I needed to figure out how to isolate them from vibration. I had planned on using sandwich mounts similar to what I used for the radiator, but I wasn’t able to come up with a good way employ them. I then spent a lot of time looking for a rubber grommet with a metal bushing like what I’ve seen on lots of OEM applications. The only aftermarket ones that I could find where intended to isolate oil and gas tanks on choppers. However, they’re designed to be installed in 1/4” thick steel brackets… I guess choppers shake a lot.
Striking out with aftermarket vendors, I decided to look for an OEM part. Abe had a Nissan GT-R in his shop and we found a some nice grommets on its oil cooler. He checked the service manual and ordered some Nissan parts:
Grommet: 18316-S3260 (Nissan calls it a “Clip-Rubber”)
Bushing: 49728-55S0A (Nissan calls it a “Collar-Insulator”)
I used 0.10” aluminum for the bracket which fits well in the grommet’s groove. The groove’s OD is about 11/16” so I used a 5/8” hole saw and then a step drill bit to open up the hole a little. Note that you can’t install the grommet with the bushing in it — duh, it took me a little longer than it should of to figure that out.
The picture below is a test bracket made of 0.10 aluminum and isolated from a weld tab with a grommet and bushing.
The bushing’s ID will accommodate an M6 or a 1/4” screw. However, I had some 3/16'“ steel weld tabs with 1/4” through holes that I wanted to use as nut plates. I was able to open the bushing ID with a drill bit to fit a 5/16” bolt which allowed me to drill and tap the existing holes in the tabs.
You can increase the stiffness of the grommet by machining or grinding the small end of the bushing which increases the “squish". It appears that the stock squish is good, but I won’t know for sure until the heat exchangers are installed. I should finish mounting them on Monday.