January 8, 2014
We now have over 400 miles on the Locost. We think we should've been able to go farther than 400 miles before things started breaking, but 400 miles on essentially a prototype vehicle is probably good, and a busted exhaust hanger isn't the end of the world. The hanger is a 1" thick piece of rubber bonded to two steel plates, and the hanger failed at one of the bonds. It was a clean break, with no rubber attached to the steel, which means we can chalk it up to a manufacturing defect and simply replace it with another hanger from the same manufacturer.
We don't know when the hanger failed. The exhaust system is strong enough to support the entire length of the tailpipe by only the nuts and bolts that attach it to the exhaust manifold, and so you couldn't tell by looking at the car that the hanger had failed. It was only because we happened to be polishing up the bodywork that we found the break in the first place, and so there's no telling how long we'd been driving the Locost like that. Which means you'd assume from all of this that there probably isn't a lot of stress on the hanger.
And yet it broke. We're not exactly sure why, but it could be from absorbing the expansion and contraction of the tailpipe. When the car is cold, the hanger is noticeably deformed, stretched toward the front of the car. When the tailpipe heats up it lengthens, so the hanger straightens out. So we've got some stress cycles there, and we're not sure how many cycles the hangers were tested to withstand, but we're thinking probably zero, since these particular hangers were likely never designed for an application like ours.
When we said that we'd simply replace the hanger, what we actually meant was we'd have to tear the car apart. To unbolt the hanger from the frame we had to remove the driver's interior panel, which meant first removing the driver's seat and seat belt, and then unbolting the seat back. So one possible change on our next Locost would be to weld a nut to the inside of the hanger bracket. We could've done that now, with everything off the car, but it would've been messy and possibly dangerous and besides, that hanger will probably never break again.
When we removed the exhaust from the manifold, we noticed that four of the six bolts had loosened to the point where they were little more than hand tight. Fearing a trend, we went over the car with a bunch of wrenches and re-torqued everything. We found a couple of more loose bolts, nothing too serious, but it had us wondering if a) we really tightened everything down when we last assembled the car, or b) some of our assemblies are prone to loosening under the rigors of spirited driving. We'll have to repeat this exercise in a month or so and see.
It looks like we have a couple of welds on the exhaust system that didn't completely seal everything up. Considering the total number of welds in the exhaust system, this isn't all that bad, and it's not like the welds are structurally weak, only that they allow a little bit of exhaust to escape. Since all of the pipes are sleeved at the joints, none of this would even be an issue except for a few molecules of burnt gasoline that managed to fight their way back into the sleeve and through the leaks to blacken the pipe at the weld.
So it's not ideal, but the good thing is, both leaks are on the bottom of the pipes so you don't actually see any discoloration unless you have the exhaust off the car. Or get down really low. Still, we'd like to seal up the leaks, and we're probably going to do exactly that. Next time. This time we just cleaned up the joints with acetone and repainted the area. Good as new. Or not new, but, you know, as good as it ever was.
Meanwhile, it hasn't been just repairs and exhaust hangers and loose bolts this week. We actually made some progress on our long-awaited, amateur-built hood scoop. After maybe six dozen coats of paint and putty to get the mold nice and smooth, we laid up the hood scoop itself, and even got it to release from the mold unscathed, or maybe just slightly scathed. Even better, the mold wasn't destroyed in the process, at least by our definition of destroyed, so we could possibly make another scoop if this one doesn't work out.
The scoop does need a little help. When it comes to fiberglassing this isn't our first rodeo, but apparently we didn't learn a lot from any of those earlier rodeos. The first thing we need to do is reinforce the scoop with a few more plies of fiberglass mat and cloth, at least in the critical areas like the flange, the top, and the sides. Then we need to fill in a few holes on the top and sides with some epoxy and micro-balloons, and finally apply another six dozen coats of primer and putty until it's all nice and smooth.
After that we'll rivet the scoop to the hood, and then start all over again with the primer and putty to hide the seams. The final step will be repainting the hood, which we're not totally looking forward to. We're thinking probably June. All of this serves to reaffirm our strategic decision early on to avoid any fiberglassing work while we were actually building the car, which would've needlessly slowed the project down. At least the hood scoop should be the last of it, so long as we don't start working on any designs for a glove box.
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