How to make frame bushings | Project Elva sports racer

On an Elva Mk VI sports racer, the tube that cradles the transmission in the rear part of the frame is a separate piece that attaches to the main part of the frame with tapered rubber bushings.

While we can easily understand the desire to have the rear section of the frame removable for quick engine and transmission service, for the life of us, we cannot understand the rubber mounting system that Elva used. Perhaps it's meant to cut down on vibration and frame cracking, or maybe it is all they had to work with back them.

Still, between the rubber bushings being totally disintegrated and the fact that the rear suspension mounts to this portion of the frame, we needed to find a better solution.

Here’s what the rear end of an Elva Mk VI is supposed to look like. You can see where the rear frame section is bolted to the front section right near the tops of the coil-overs. The transmission bolts into this rear frame section as well.

Here’s a close-up of how the two halves of the frame are sandwiched together with a rubber bushing and a metal bushing holder.

This is a close-up of the frame rail. A raised area holds the metal bushing holder. A stud is threaded into the end of the frame rail and then the tapered bearing is tightened, thus centering the frame rail in four different mounting positions like this one.

And here is the condition of our original bushings that we had to deal with. To say that getting accurate measurements from these rotten bushings was difficult is an understatement.

Our plan is to take as accurate measurements as we could, put these measurements into a CAD program, and then print test bushings out with a 3D printer. If these test bushings fit well, we could then duplicate them on our lathe in Delrin, which would still offer some give but would allow much less suspension deflection.

Classic Motorsports staffer Tom Suddard took dimensions to run through his 3D printer.

Pretty quickly, the bushings appeared on Tom’s computer screen. The orange bushings in front of his laptop are what he was able to create with his 3D printer.

Once we determined that the orange test bushings fit perfectly, we replicated them in Delrin. On the wall, you can see an illustration with exact dimensions marked for each phase of the machining process. We used a Smithy machine for this work.

Here you see (from left to right) the original bushing, the test bushing as it came out of the 3D printer, a white test bushing that we machined and the final bushing in black Delrin.

We were missing one of the original bushing holders, so we turned down a piece of tubular steel stock and then drilled and welded the correct size washer to the bottom to duplicate the original bushing holder.

And here’s the finished product. We now have eight nicely painted bushing holders and new bushings that fit perfectly. We can now bolt the two halves of the frame together and test-fit the transmission and the rear suspension that we have nearly completed.

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View comments on the CMS forums
RoddyMac17 Reader
1/5/22 6:26 p.m.

Those look like Spridget front suspenion bushings, the ones for the shock to trunnion (88G264).  But, they should work much better in solid delrin than rubber.

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