Monthly Archives: November 2014

Mounting the Side Impact Panels

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Side Panel

Aluminum side impact panels finished and mounted

SCCA Formula 1000 rules require side-impact protection consisting of either kevlar laminated to the inside of the body, or 0.060″ aluminum or 18-gauge steel bolted to the frame. To keep the side impact panels from being used as a stressed member, attachment points to the frame must be more than 6″ apart. Mine are laser cut from 1.6 mm aluminum. The mounting holes were also cut by the laser to be sure of the 6″ rule, but this was a mistake as it made the mounting tabs much harder to fabricate. It would have been much easier to weld the tabs in place with holes already drilled, then drill through the tabs to the aluminum panels for exactly aligned holes. As you can see from one of the photos below, the panels fit perfectly. This project was a lot of cutting and welding with little apparent progress.

Building the Axle Halfshaft Extensions

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Rear Suspension

Rear suspension, axles and differential in place

The car will use standard Honda Civic axle halfshafts, and I had the choice of cutting, sleeving and re-welding them, or building extenders that effectively widen the differential to meet the unmodified halfshafts. The cut/sleeve/re-weld option would eliminate the axle hardening and leave unknown strength, and I’ve since seen an example where this was done and the axle broke right at the weld. The option of “widening” the differential has several advantages. First, we can easily replace the halfshafts if necessary in the future with off-the-shelf parts. Second, moving the inner constant-velocity joint closer to the plane of the control-arm pickup points minimizes the plunge, or change in length, required as the suspension moves through its travel. Third, the halfshafts become equal length, eliminating torque steer. Now you may say “but, the extensions will be of different length and will twist unevenly so the torque steer won’t be eliminated”. The extensions will be much stiffer than the axle shafts so that won’t be the case.

So the choice was clear. We started with a differential and a couple of halfshafts as raw material…

 

Mounting the Rear Sprocket

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Mounted

Rear sprocket mounted on the differential

The limited-slip differential is a torsen or quaife type made by OBX, imported from the USA for an American-style Honda Civic. The differential ring gear on American Honda Civics is mounted with left-hand threaded bolts, so I blithely go down to the auto recycler here in Thailand and buy a differential for donor parts. Hmmmm… these bolts don’t fit. So I check carefully and find these differentials are sold in Thailand with right-hand threads! I go back to the auto recycler and ask for left-hand threaded bolts. They just look at me with that “crazy foreigner” look. OK, all we have to do is order some American-style bolts from Ebay US… There is exactly one listing on all of Ebay, and they don’t ship to Thailand! Plan B: drill the suckers out and use through-bolts.

This is where I find out the differential housing is made of some ultra-hard tool steel, or maybe kryptonite or something. Wow, are these holes difficult to drill out. Solid carbide end mill, highest speed on the milling machine, lots of lubrication, and wait. And wait. And wait…

Next we had to drill a matching hole pattern in the rear sprocket, then cut it in two halves for quick changing at the track. This sprocket will be for static test only as the new hole pattern wasn’t compatible with the old one, leaving thin aluminum in some places. I’ve since ordered a blank rear sprocket from England which I will cut with only the correct holes.

Fabricating the Differential Mounts

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Finished Diff

Finished differential, differential mounts, and rear sprocket

Thirty-four years ago I designed a car for the SAE collegiate Mini-Baja competition. The differential was inadequately supported in the middle, and although it didn’t break on us, it broke the next year and sidelined the car. I’ve felt guilty ever since, so that’s one mistake I’m determined not to repeat. This one should be adequate…

Later I plan on fabricating some sort of container or plugs to keep the oil in the diff.

Removable Engine-Compartment Frame Rail

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My original plan was to make the engine install from the bottom as I’d owned Porsche 911s for most of my life, but feedback on the ApexSpeed.com forum made me change my mind. The change was fairly simple, requiring only making the upper right engine-compartment frame rail removable. Taking an angle grinder to cut a big chunk out of my finished frame definitely made me measure seven times, cut once.