Jerry Feather

Hi Alan. I showed the original plastic cover to my Plastics guy and he said he thought it is Poly Propolene, I think, and he commented that it is "really cheap." I don't know how heavy the current covers are that are available, but Roger says in this thread that they are a little more robust than the earlier ones. I haven't miked my original ones but I think they are about 15 or 20 thousandths thick. I wonder how thick the current ones are.

If you look at the pictutre of the wooden form I showed above you will see a strip of aluminum screwed to the front edge. That is the part of the form that will make the slim channel to go over the sheet metal in the car in front. I don't think it is going to be a problem to form over it. The main problem that I think we are going to have is getting the formed plastic off of the forms.

One of the last things I will have to do with my forms is drill very tiny holes all over each one so the air does not get trapped between the form and the plastic in the sucking process. There needs to be enough holes in the corners and groves so that the air will go out in a rush rather that taking a few seconds even. The forming process needs to take place when the vacuum is introduced in about 2 or 3 seconds, especially with plastic this thin to start with because as soon as it hits the form it will cool and not form.

Jerry Feather

yardpro

jerry.... you ARE the man....

what a lot of time and effort in these..

that is what i love about these cars and this place.... people like you interest in improving them and keeping them alive... cause you surely are not going to make a lot of money off these parts...

Thanks

dcrasta

Wow Mr Feather, Impressive as usual. Carry on sir (Subscribed).

Please add me to your S3 list .

Ducman82

If u need an OB tester, let me know

dprantl

Jerry, if you are making the cowl cover from a thicker/more sturdy plastic, you may not need the fins at all. It seems to me that the fins are there on the stock piece to reinforce it since it is very thin. On other cars where the cover is made from more sturdy materials, there are no fins present.

Dan
'91 928GT S/C 475hp/460lb.ft

WallyP

"One of the last things I will have to do with my forms is drill very tiny holes all over each one so the air does not get trapped between the form and the plastic in the sucking process. There needs to be enough holes in the corners and groves so that the air will go out in a rush rather that taking a few seconds even."

Why not arrange a manifold or an overall air chamber connected to all of the little holes so that you could introduce air pressure to help remove the part?

Jerry Feather

Hi Dan. Thanks for your input. That is a very valid point about the fins. Making these covers without the fins would haver been somewhat easier, but then the resultiing cover would not look much like the originals. I am not trying to make something that draws attentioin, like someone looking and saying "that is one of the Jerry Feather covers," but rather one that is not really noticed as with the originals. I think the fins will help with that and even on the ones that don't have the bottle opening provision on the end.

I don't think that the fins will cause the plastic to lock itself on the form, but my plastics guy is not so sure. He pointed out that the originals seem to have some relief or taper to them where mine don't. We are going to try to form a couple of these probably next week and see how it goes. If we have some problems I may very well have to remove the fins. Or, if the problems are too great I may just have to abandon this project. We will see.

Jerry Feather

Jerry Feather

[QUOTE Why not arrange a manifold or an overall air chamber connected to all of the little holes so that you could introduce air pressure to help remove the part?[/QUOTE]

Hi Wally. That is actually a common practice in this vacuum forming process, but one I hope to be able to avoid. It would/will add a lot of complexity to this project, and I haven't given much thought to just how I would accomplish it.

Thanks for your input.

Jerry Feather

Alan

Jerry - I imagine you could sand a little taper into those ribs pretty easily - no? It wouldn't take much to make the release easier. I agree keeping the ribs is good for strength and keeps both a more stock like look and a bit more interest in the flat area of the panel.

Alan

Andre Hedrick

I happen to be filling mine with JB Weld and drywall fabric tape to make a bottom side casting, and who knows it may last forever, now.

Jerry Feather

Alan, if you form some plastic down over a form that has straight sides when the plastic cools enough to get hard again it will lock itself on the form. If you form the plastic down inside a form that has straight sides when it cools it will pull away from the sides and come right out.

I think what my plastic guy is doing is thinking of the ribs from the down-over aspect, but I am thinking of them from the aspect of the plastic down inside or in-between two ribs. I think I am going to be right about that.

Where I think we are going to have some difficulty may likely be pulling the formed plastic up off of the metal strip we are going to form over for the front mounting narrow flange. However, even that one will be pulling away from the form, I think, except for the slightly different angle it will have in respect to the rest of the form.

Jerry Feather

Jerry Feather

Now, I find that I am going to have to back up a little and correct another significant design flaw I have just found in the original cowl cover.

I took an opportunity to casually look at one of these covers in one of my other S4s that still has one in it that is in pretty good shape, but I looked at it from behind the hood with the hood closed. OOPS!! I see that the back curve of the plastic cowl cover does not match the front curve of the metal cowl piece that it it mated up to; and it is off quite a bit, about a quarter or 5/16 inch on each end.

What I did just to be sure was grab one of my spare metal cowl pieces (you all have several of them lying around, don't you?) and took it out to the shop and compared it with one of my new forms. Same result. Now I see that my other improvement in these, with the seal, is not going to be effective unless I get the back curved edge to match.

I think I have figured out how to do it without starting completely over; and the fix will not be too obvious as such, I hope.

Of course I should have started this design with the metal cowl in the first place, but I had presumed that the original plastic cowl cover was properly designed, at least at first; and I have had it in the back of my mind that I should be using the metal cowl piece to determine this curve.

Jerry Feather

Jerry Feather

Thanks. One thing you can do in preperation for the test is to check in your 81 to see if there are three (or how many?) clips under the metal cowl trim piece just below the windshield into which the rear edge of the plastic cowl cover is intended to be inserted upon installation. Also you could just confirm that yours has or maybe had one of the original partial (2/3) covers.

Jerry Feather

Jerry Feather

At this point in this development I have mostly completed my feeble analysis of the whole program of plastic cowl covers and the rubber trim seal that is associated with them along the front edge. It's feeble because I still don't have answers to some of the questions I have had, so I have had to guess about some of that.

My first conclusion is that the plastic cowl cover was put in the first cars with the purpose of directing the water that is being wiped off of the windshield away from the heater blower intake and perhaps from the WSW motor. I think the reason that the first covers were only partial is because the bulk of the water coming off of the WS is wiped down principally on that side of the windshield because the water coming off of the driver's side is pretty much up and to the side rather that downward as with the other side.

I have to assume that the full length cowl cover came in with the high intensity washer feature, and I think that may have been with the 85 or 86, since I have seen a number of what I think is the first full length version (that we are referring now to those for the"S3") on at least MY 86. I'm not sure about 85. That version has the cut-out for the washer bottle. That version also is the first with the opening for the heater vent. I suppose there was no need for this opening when so much of the cowl area was open to the fresh air having no cover over it.

I think the full length version was possibly created solely to provide a more cosmetic cover for the cowl to hide the washer bottle and the WSW apparatus in that area.

I can't even guess at why the S3 version was changed, someting in the MY 87, I think, because I have seen pictures of the S3 version in some 87s, but I think the washer bottle hole was reduced in size and the design was changed a little bit. The two little flat areas in the rear outer corners were removed. In addition, the design of the opening for the heater vent was substantially simplified from a kind of double fense to a single fense design. I think I will refer to this third version as the S4/GT version, because I think that is how long it lasted.

Finally I think the last version of this Cowl Cover created by the factory is the one that has been shown above in this thread and which I usually see in the GTS cars. It is very similar to the S4/GT version except it has a fairly large and ugly trough from back to front just to the drivers (LH) right of the hump in the center and in fact "takes out" a portion of the center hump on the right. I have concluded that the trough was put there because of whatever testing may have been done probably revealed that the WSWipers were sweeping a bulk of the water off the WS just in that area and the S4 version of the cover actually has a sort of dam between the center hump and the heater vent opening fense that was likely causing the water to puddle and back up to drain down the back of the cover and into the cowl area where it is not wanted.

I also think that they may have failed to notice that perhaps the main reason the water was pouring down the back of the cowl cover was more associated with the fact that the cowl cover did not fit well in that area and that the ledge in the back under the metal cowl piece is not designed to drain water anywhere but over its back edge. There are two humps in that ledge toward the outer ends that create a puddle place right in the middle of that ledge. So, most of the water off the windshield was going down the back of the cowl cover and onto or maybe into the heater blower, but not for the reason that I think was concluded. The two humps in the back ledge are there to cause those ends of the back of the cowl cover to conform the the shape of the metal cowl piece to the rear of the cover because the front edge of the metal piece does not have a continuous verticle flange; rather it is narrow for some reason in the outboard area and had no clips underneath, so the cowl cover itself needs to hold itself down to the correct contour. I think a lot of thought went into that part of the design, but I am amazed that they did not notice that the back curve of the plastic cowl cover doesn't match the matal cowl piece, and that may very well be the reason water can go down the back.

I still wonder now if this GTS version of the cover is the one that is available from the factory. I also wonder now how much the factory version of this cover, whichever one it is, has gone up, as Roger has announced with other 928 and maybe all Porsche parts.

In looking at pictures of 928 engine compartments since my attention had been drawn to these covers I have noticed that there may be a many at 15 or 20 percent of the cars out there totally without the cover, and most of them are also without the trim seal that seperates the cowl area from the engine compartment.

I may not seem important, but the bulb seal that fits along the front edge of the cowl area clearly has the purpose of keeping the air and gasses in the engine comparment out of the cowl area. Probaly the sole reason is to allow for fresh air only into the heater motor opening in that area and to exclude air from out of the engine area. If you look closely at the underside of your hood in that area you will notice that the trim seal is or was actually making a slight mark where it is/was touching the hood framework.

I'm still working on the forms and hope to have them ready to try forming this next week.

Jerry Feather

heinrich

Yes.

I recommend you redesign the cowl cover according to your above post. It will look and function better and last longer.