An M.G. Locost Build

November 12, 2011

Back on schedule. We built a new UCA jig in just a few hours on Friday, having had lots of practice, and filed the fish-mouth ends on the new upper A-arm tubes during the 49ers game on Sunday (27-20 win over the NY Giants, woo hoo! Sorry if you're a Giants fan, but the 49ers have been so bad for so long). We also finished trimming the lower control arm brackets, a seemingly never-ending job.

  Spiffy new LCA brackets
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These brackets will carry the lower trunion of the MGB kingpin assembly, and will also support the lower shock mounts. In your typical MGB Locost build, these are often just big hunks of box-section steel welded to the A-arms. We felt it was important to integrate them better, and also to round off the outer edges, because that looks like something real automotive engineers would do. So we took the extra time, and we think they turned out excellent, although they may not look like much in this photo. Or in person.

The only problem is, we're wondering now if they’re strong enough for the job. Most of the weight, cornering, and braking forces on the front tires are going to be transmitted through these brackets. At 3/16” thick, the lower suspension bolts have only .09 square inches of steel to work with. With a yield strength of 36K psi, the brackets could start to deform at 1800 lbs. That may be okay for you, but it seems to us a little close to the edge. You never know when a curb might jump out in front of you. So we'll have to give that some thought, and maybe weld on collars or something.

The Locost workshop  
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On a happier note, we’ve added a drill press to the workshop. It’s a table model but it’s still pretty big. It's got a laser sight and everything. We wish we knew how to use it. We got the drill press originally for those suspension bracket holes that have to be just right, but the more we use it, the more we realize we should be drilling all the holes with this thing. It’s very precise, and a lot more powerful than the hand drill. The only problem now is that with all the new power tools on the workbench, there’s no room left to actually work on anything.

  Cutting holes the easy way
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Another piece of good news was how well our new set of hole-cutting saws, a whole box of them generously loaned to the project by my brother, works on 1/8” mild steel. The lower control arm shock support brackets were kind of overkill in terms of size-to-weight, since the pieces are mostly used as spacers and vertical support, and the horizontal part doesn’t see a lot of stress. By cutting 2” holes in the middle of the brackets, we knocked 25% off the weight and the pieces now look totally pro. Good luck doing that with a hand drill.

Semi-professional shock support brackets  
click to enlarge

It's hard to imagine any part of this Locost build being more work than the A-arms. I hope that’s not just because we decided to do them first. We know there’s plenty of heavy lifting ahead—literally and figuratively—and a lot more cutting, drilling, trimming, and even filing to do yet. But the A-arms have really tested us, both mentally and physically. Twenty tubes altogether, along with assorted brackets and fittings, at least four do-overs, and 28 fish-mouth ends to file at 2-3 hours per. Plus all of those jigs. It may be awhile before the hands and fingers recover.


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