Monday, February 13, 2012

Windscreen

After a few months of sitting there waiting, procrastinating, distractions, and whatever, the windscreen is finally in. Over the last couple of months I had put the screen in place several times to check fitment, and had always had a problem with getting the rubber seal along the bottom of the frame to fit nicely against the curve of the body. In effect the rubber was not forming to the body curve well, and thus the frame was sitting too high off the body. Cracking the glass is a very real possibility if you start pushing on the frame, so I avoided this. I knew the problem was partially because the rubber was "gripping" the body through friction, but also I thought the rubber was just resisting the distortion that the screen frame wants to put on it when the frame is placed in position. It seems I was wrong about that.

The bottom of the frame does not actually touch the body. The rubber sits on the body, and curves to follow the frame/body curve. A fellow Cobra builder suggested lube on the rubber seal, so I gave the rubber a generous coating of rubber grease, and it slipped right on, followed the body curve beautifully and I'm very happy with how it turned out.


The CR manufacturer-supplied build manual suggests a measurement of approx 1070mm from the top of the screen to the rear-top of the transmission tunnel. I used this measurement initially to place the screen, but it looked a bit too upright. to me. To check my eye I protracted the angle off an A2 size poster side-profile picture of an SC427 Cobra, transferred the angle to my Cobra, and it calculated out to be more like 1045mm on the CR body. So I used this measurement to end up with the screen rake you can see in the photos.




The windscreen is made in England, and is made from chromed brass. The mounting legs on the windscreen are too long by design, so after positioning the screen, marking, removing and drilling, the excess few inches is cut off and I rounded off the sharp edges.




The CR chassis/dash rail has the mounts for the screen already in place complete with slotted holes, so it's a fairly simple process to position the screen, mark where you need to drill the windscreen legs, remove, drill, and then bolt it in place.

There is a small chrome bracket at the centre bottom of the frame which bolts through the top of the dash. To ensure I got a nice flat fit between the bracket and the top of the body I removed the bracket from the screen and bent it slightly more than it was already. I haven't drilled and bolted this small bracket yet, as I'm sure at some point during the rest of the build the screen will probably be coming off again for one reason or another.


 



To allow for millimeter variances in chassis build and windscreen build (both use manufacuring jigs and some high-tech like laser-cutting of course, but at the end of the day both are made by hand so there is always a tolerance) and ensure the mounting legs actually fit in the space, the chassis mounting holes are purposefully placed too close together - each mounting plate sits about 5-8mm away from the windscreen mounting leg. This gap is bridged with a few washers, being careful to pack it as much as possible so that when the bolts are tightended any distoriton is kept to a minimum to avoid possibly stressing the frame and cracking the glass.




There have been people who have had a good windscreen one night, and woken the next morning to a cracked screen. This appears to have been caused by some amount of chassis twist after racing/driving and resultant stress on the frame. I seem to have gotten through the install and well past the first 24 hours without cracked glass, so hopefully my install has not placed any stress on the frame. Time well tell.







The escutcheon plates are not on yet either, as they dont go on until after paint - and believe me that is a LONG way off!

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