Rear Window Protection

Chuck · 03-31-09, 11:04 PM

The rear window quickly gets discolored from proximity to the Webers. The fuel vapors discolor the window.

Before putting in the new window would like to do something to protect it.

I am planning on adding a thin sheet of Lexan, about 10" wide by 20" long, to the inside of the window, held in place with several small screws through the rear glass. The plan would be to replace the sheet of Lexan when it becomes discolored. It would me MUCH easier to replace a small sheet of thin Lexan rather than the entire rear window. It would be relatively inconspicous, mounted flush on the inside surface of the rear glass.

The question: Is Lexan a suitable material? It is readily available and not too expensive. Better heat resistance than plexi glass. But not sure if it is sufficiently heat and fuel resistant to be set a few inches above the Weber intakes.

Any ideas?

We don't want to mount the flat cover over the Webers, seen on the original GTs. Want to keep the look of the eight throats under the glass.

Ian Anderson · 04-01-09, 05:17 AM

how about a tempered glass sheet mounted in the same way as the originals

stops the reversion and yet still shows off the carbs

A decent glazier would do this fairly quickly and round off the edges to avoid cuts

Ian

Mike Pass · 04-01-09, 06:48 AM

Go for a glass window - easily cleaned - problem solved. I don't know about ease of supply in the USA but most replica people should be able to get one for you. They are easily obtained in the UK for about £65.
Cheers
Mike

Chuck · 04-01-09, 03:45 PM

My recollection is that there is a tiny bit of flex when the sides of the rear window are screwed down. Not sure how that would do with real glass. To late to alter the fiberglass to fit flat, since it is painted. Thanks for the idea.

A bit more research indicates that Lexan / polycarbonate becomes flexible aroung 385 degrees F. It would seem therefore, that the idea of using a thin piece as a sacrifical protection over the carb would work. I can't imagine it getting that hot in that space.

Rob · 04-01-09, 07:16 PM

Hi Chuck,
Yep...this is an issue, especially with fuel and fire spitting webers. This is why they used the top pans back in the day.

Mike Pass · 04-01-09, 08:13 PM

The proper glass rear windows are curved (not just a flat piece of glass) and all the ones I have seen fit very well in a wide variety of bodies from different suppliers. Most of the rear clips seem to be very similar around the rear window aperture. The best way would be to check one for fit in your rear clip.
The angled tray above the carbs on the original cars was not to keep flame spit off the rear window. The engines tended to spit a bit of flame on startup after a few good pumps to prime but the flames were quickly sucked in when the motor fired. The main aim of the plate was to help with stand off. Engines using webers can often have a stream of fuel particles coming in a stream OUT of the carbs at particular revs especially with a race cam. This standoff can drift away from the carbs which creates a hazard and can upset the mixture quite a bit. The plate ensures that the stand off fuel cloud gets back into the carb rather than it getting everywhere. Resonance in tubes is a strange thing and can be more relevant than flow along the tube. This is why inlet and exhaust lengths are so important.
Cheers
Mike

Chuck · 04-01-09, 09:51 PM

Rob, Mike:

Interesting points. One wonders why more reproductions don't add the top trays to not only protect the glass / plastic but also enhance the peformance of the Webers. Perhaps it is the asthetics of the carbs - if you got 'um, flaunt 'um.

I recall seeing a picture of a top tray made from a thick piece of a clear plastic material, I would assume polycarbonate, in the same shape and location as the original. That idea is starting to make more sense, although it looked a bit strange to me.

Eric Johnson · 04-01-09, 10:15 PM

Quote:

Originally Posted by CESLAW

Rob, Mike:

Interesting points. One wonders why more reproductions don't add the top trays to not only protect the glass / plastic but also enhance the peformance of the Webers. Perhaps it is the asthetics of the carbs - if you got 'um, flaunt 'um.

I recall seeing a picture of a top tray made from a thick piece of a clear plastic material, I would assume polycarbonate, in the same shape and location as the original. That idea is starting to make more sense, although it looked a bit strange to me.

Chuck,
Maybe this is what you're looking for:

Chuck · 04-01-09, 11:15 PM

Eric:

That would be the one!

Would you know what material was used? Polycarbonate / lexan?

Chuck

Eric Johnson · 04-02-09, 10:20 AM

Chuck,

I'm not sure. Probably polycorbonate Tuffak I would think.It's not my setup, I saved the pic from the archives awhile back.
Maybe the owner of the car will see the post and respond.

Randy V · 04-02-09, 08:35 PM

Polycarbonate and Lexan are the same thing.. I would think that the Lexan would be longer lived that Plexiglass which breaks easily from vibration. However - I don't think that it will retain it's clarity for long as it's not likely to like the fuel reversion cloud above your Webers if you have a long overlap in your cam...

It might be one of those things that you have to replace once a year or so..

Chuck · 04-02-09, 11:42 PM

Randy:

I suspect you are right about replacing it from time to time. That is why I plan to put a piece 12" wide by 21" long on the inside surface of the rear Lexan - it will be a whole lot easier than replacing the entire window. We will see how it works.

Just re-installed the rear window tonight. With the trimming, drilling the holes, etc. it takes me several hours. Don't won't to repeat the process any more than necessary.

Randy V · 04-03-09, 10:55 AM

Chuck - I just got to thinking.. On the NASCAR cars - those boys have a couple of thin lexan sheets (tear-offs) on their windshields. They tear them off as needed during pit stops.

I wonder how hard those would be to come by?

They could potentially be placed on the inside of the rear window - thereby killing two birds-one stone..

Randy V · 04-03-09, 11:12 AM

Hmmm... Not very hard to come by at all..

They are a Polycarbonate Mylar Film.

Seems like Google Search brought up a number of them just be searching Windshield Tear Offs.

Here's a couple;

Welcome To Tearoffguys. Windshield tearoffs, Paint Protection, and Vehicle Wraps

Your Racing Products Online Superstore - Windshield Tear Offs

I've also sent an inquiry to 5-Star products (whome I have bought Lexan windshields from before)..

Chuck · 04-03-09, 11:47 PM

Randy:

As I was driving to a meeting today I got to thinking about the 3M protector material I had applied to the front end of the BMW to protect it from dings. Really tough stuff and adheres very well. Placed a call to the guy that installed it to see if it might work inside the rear window, but, alas, it was a warm Friday afternoon and no one was around.

Then I saw your post. Had not heard of that material before but sounds like an EXCELLENT option.

My concern would be the heat from the engine causing it to separate from the window and then dropping onto the hot, fuel laden, carbs. That could cause some real nastiness. So would need to make certain it would be safe in this applicaiton. Keep me posted on what you learn.

This idea would be a whole lot cleaner and easier than a piece of sacrificial lexan.

Chuck

Dimi Terlecky · 04-04-09, 12:21 AM

Hi Chuck

Having read all the posted suggestions there is only one way that will be permanent and not cause further grief and is the correct way to do this and that is to fit a real glass rear window.

I have a DRB which was supplied with a "polycarbonate/lexan/plastic" window which I chose not to fit for all the above reasons and purchased a glass window from RF which fits and resolves all these problems permanently.
The clarity of a glass window is second to non and will not deteriorate with time.
There is no other fix.

Dimi

Randy V · 04-04-09, 09:49 AM

While I agree with Dimi re: real glass - I would be concerned about the flexing of the rear clip when opening and closing. Perhaps the bonding of the glass would strengthen it from flexing quite so much - but then that would make the rear glass a structural component of the clip and put it under some degree of stress..

Chuck - I've not yet heard back from 5-Star and I'm sure it's because they are quiet busy servicing their bread-n-butter customers right now as racing season is upon us..

I've had a though concerning the heat you mentioned (quite appropriate)...
I wonder if there would be some sort of retention that you could put at the top and bottom of the lexan mylar tear-offs to grab hold of it and not let go until properly released?

Sandwiched between the lexan and the body?
Hmmm.. Rather a pain but cheaper and easier than removing and replacing the entire window...

I'm going to think on this a bit as I don't think the idea is dead just yet..

EGLITOM · 04-04-09, 06:33 PM

Hi Chuck

why not making this out of laminated security glass. THis withstands the heat and should keep clear and easy to maintain.

IMHO i like th look of the screw down rear window. From what i could see the original cars have them as well. May be besides the mark III cars glass is not original and dilutes the look of the car.

TOM

Eric Johnson · 05-29-09, 02:33 PM

Quote:

Originally Posted by CESLAW

Randy:

I suspect you are right about replacing it from time to time. That is why I plan to put a piece 12" wide by 21" long on the inside surface of the rear Lexan - it will be a whole lot easier than replacing the entire window. We will see how it works.

Just re-installed the rear window tonight. With the trimming, drilling the holes, etc. it takes me several hours. Don't won't to repeat the process any more than necessary.

Chuck,

I was wondering what your ultimate solution was for your rear window? I like the tear off idea myself. What did you end up using?

Chuck · 05-31-09, 07:57 PM

Eric:

As of this time I have done nothing. Interstingly, with the carbs reasonably tuned and the filter screen in place I have not yet noticed any discoloration or spotting with about 150 miles since the replacement Lexan has been in place I may just take my chances and let it go for now.

Chuck