An M.G. Locost Build
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May 21, 2012
Back on Track

We're still waiting on our latest shipment of metal stock, so the rear transmission rails are still MIA. But that isn't stopping us from moving ahead with other tasks, most notably installing the suspension brackets, one of the most critical steps in the entire build. By using jigs to locate the brackets front and rear we're minimizing our mistakes, although we're not eliminating them entirely as that would take all the fun out of it.

  Early version of the front suspension jig
click to enlarge

The jig in this photo has since been modified. The original jig had the upper and lower brackets 7" apart, since our two-dimensional PowerPoint sketch has them 7" apart. In real life, however, which has three dimensions, the actual space between the brackets is 7-7/8", because the lower brackets are set 3-1/2" inboard of the uppers. At first we thought this measurement gaffe would mean we'd have to build a whole new jig, but then in a Forrest Gump moment we realized we could just saw it in half and glue the two halves to a bigger base, with the extra 7/8" between them.

That worked shockingly well, however not before we'd used the jig to install the nearside front upright (FU) tube. Because the FU and LB tubes aren't parallel, this resulted in the top of the FU tube leaning 3/32" too far inboard, which was unfortunate and disappointing, but based on our new expanded Locost disaster scale, only a minor annoyance. Still, it would've been too painful to cut out the freshly-welded FU tube, so we were left with two options: add a shim between the tube and the bracket, or make a new, slightly longer bracket. We went with the longer bracket. It's barely noticeable. Don't tell anyone.

Rear suspension jig hasn't failed us yet  
click to enlarge

The rear bracket jig is much simpler because the brackets are welded to vertical tubes, which means the distance between them in three dimensions is the same as it is in two. The brackets aren't centered on the M tubes because the trailing links need to clear the K tubes. Some builders install the brackets flush on the inboard side of the M tube, which has the advantage of not sticking into the passenger compartment and jabbing the driver in the side, but we weren't comfortable with that from a structural point of view, so we offset our brackets 7/8" outboard and 1/8" inboard.

  Gusset for the upper shock mount
click to enlarge

We also added the rear shock mount gussets. The book gives almost no information about how to make these, but we determined that 16 gauge steel would do the job, based in part on our extensive engineering experience, and mostly on photos from other Locost websites. The big breakthrough with these gussets was not that we managed to get them welded in without ruining anything on the frame, but that we cut them out in minutes with the angle grinder, instead of hours with the Dremel. I'm not sure any of us quite realize yet what a huge impact this is going to have on the build schedule.

Gusset weld almost good enough to post online  
click to enlarge

We were pretty happy about the welds on the gussets, partly because we didn't blow any major holes in the thin sheet steel, but mostly because you can look behind these welds and see how well the filler wire penetrated into the base metal. The beads weren't bad either, and overall we're pretty excited about our welding progress. Our next Locost frame is going to be awesome. As for this frame, we're starting to think we can do all the remaining welds ourselves, and not farm anything out, even the critical rear suspension bits. We'll see how the seat belt mounts work out.

Over the weekend we trial fit a few more donor parts, and it turned out the steering rack we bought off eBay last year was the wrong model. It's from a later MGB, one of those rubber-bumper cars. We should've saved the rack from the donor, but it was kind of rusty. I suppose we could make the later rack work, but it has a slower turning ratio than the earlier cars, which was a lame attempt by British Leyland to lighten up the steering effort without spending money on power assist. So we bought another rack off eBay, an early model, at a bargain price of just $52.50. Can't wait to see it.


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