An M.G. Locost Build
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October 1, 2011
Suspension Work

Work continues at an incredibly slow pace. We built jigs for both A-arms, and we've been cutting tubes for the suspension, but it’s taking a while. We started by cutting all 13 bushing tubes, plus two spares, to a length of 1-7/16” per the book. We ground them individually using the new disc sander and dial caliper to get them all within .005” of 1.4375”, but found we could only take off about .01” at a time before the tube was too hot to handle. So that took some time. But they're done now and they look great to our untrained eyes.

  Book-size bushing tubes
click to enlarge

Fresh off the success of constructing these shiny metal suspension pieces, we cut some tubes for the upper and lower control arms with the chop saw, and by using careful measurements taken directly from the plans, ended up with 3 of the 4 lower A-arm tubes too short, or so it seemed at the time. In the process of fitting the one remaining tube to the jig (a four hour job—more on that later), we ended up having to remove a good 3/4" from the length of the tube. So clearly our measurements were off, and just like that, the three discarded tubes were back in play.

Later, we kept looking at the new bush tubes and started wondering how they’d look in the planned 1-3/4” suspension brackets (1-1/2” inside dimension). That’s only 1/32” of clearance per side. We couldn’t see that working in every situation, and metal-on-metal screeching from the suspension wouldn't be fun to hear at an autocross or on the track. So we shortened one of the spare tubes to 1-3/8” (1.375”), then pressed one of our rubber bushings into it.

Squished bushing  
click to enlarge

That didn’t work at all. Rubber squeezed out of both ends at least an eighth of an inch, making the assembly more than 1-5/8” wide. And while we might be able to jam that into a bracket that's only 1-1/2” wide, we're pretty sure suspension movement would suffer. So we're going to leave the rest of the bushing tubes alone, and switch over to 2” brackets, with a 1-3/4” I.D. We think the wider brackets should still fit, giving us additional clearance and more space for adjusting out any build discrepancies. Which we may need. You never know.

With that mess cleared up, we were able to finish the lower A-arm tubes. While filing away on the first of these, two things became apparent, one good and one not so good. The good thing was that our half-round bastard file (that’s what it’s called, not a comment on its usability) turns out to have a radius of curvature that's exactly the same as the bush tubes—half an inch. Coincidence? Maybe, but we're not complaining. By using the file carefully and judiciously we can make perfect fish-mouth cuts. At least on the 1" tubes.

  Filing suspension tubes
click to enlarge

What was not so good was the realization that getting the angle of the fish-mouth, the alignment of the two ends, and the length of the tube to all meet in one happy place is a major chore. It can be done, but it requires an amazing amount of test fitting, and only one or two swipes with the file each time as you’re getting close. And when you do get close, you’d better hope the length of the tube is very close, too. You can’t build in any manufacturing tolerances, like slotting a hole or shimming. It has to be just right.

As the A-arm building process continues, it’s beginning to dawn on us how much work this is going to be. And some of it won’t even be this much fun. If we think about building a single A-arm to fix a broken part on a production car, it wouldn’t be too bad a task. If we had to replace ALL the A-arms on a car we could take it on as a semi-major project. On the Locost, this is just one project out of 50 major projects. Each and every component of the car has to be installed, and at least half of them built before installing. Our odds of completing this? We're generously giving it one chance in three.

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