How to repair plastic/vinyl air dam (69 BB w/ AC)

[JohnZ]

Those were self-tapping sheet metal screws (like those used for gas and brake line clamps), not machine-thread screws; the holes in the subframe were just drilled, not tapped.

[BlackoutSteve]

This is confusing because the brake line clamp screws are a machined thread with a thread cutting flute.
Gas tank strap screws are a sheetmetal tapping thread with a point. The two are quite different. 

Brake line screw 3958062 / B-10412 http://www.amkproducts.com/bulk3.asp?part=B%2D10415

This is the kind of screw I expected to see used here but, without the hex-flange because a separate washer is used. No where on these cars have I seen a hex-flange with a washer. Only hex with washer or hex-washer.

Gas tank strap screw 9420065 / B-12108 http://www.amkproducts.com/bulk3.asp?part=B%2D12108

[BlackoutSteve]

Sorry, I thought gas tank straps for some reason.. Forget that last B-12108 example..

Still, the threads on those fuel and brake clips were machined threads with the tapping flute and not regular self-tapping type. 

[NoYenko]

Steve & Mark X22, I finally found the missing Air shield screw I was looking for. I thru it in with my front end sheet metal bolts. Any way I am sure this is it because when I took it out I remembered it was ground on one side like it hit the pavement or something. I am now questioning if the other holes I measured as .250" were filled in slightly from powder coating. I hate to put a 5/16" tap into it and open it up more but I have to find out what size bolt goes in there.I will let you know.
George

[mark x22]

5/16-18 tap size is .257

[big iron]

Has the correct size screw configuration been determined?
There is something wrong with the 69 AIM C60 B4 UPC.
From an assembly standpoint I can not imagine a line worker having to stack 9 washers on screws and installing them while holding up the shield. It would be more efficient to have a washer and screw asm.
The screw hole piercings of .277/.281 would only work for a self tapping 5/16-24 or 32 if I am correct.
The only screw I think would work using the bolt and washer assumption is an over sized self tapping screw ( hex head wo/ washer) used on the front sway bar. Rick's shows them  as SS-415 and are used when the screw holes are stripped. Bob

[z10kl]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=220947515192&ssPageName=ADME:B:SS:MOTORS:1123
Here is an early LA built car that I noticed the holes for the shield on the underbody pics. Looks like 09B

[9T4Z]

Hijack:  for all their 'knowledge' the Hendrick group advertised it as a September 69 build! Love to see the protect-0-plate

[NoYenko]

Mark,Steve & Big Iron, I pulled out the subframe, check the bolt holes for air shield they are all 5/16" X 18 in the sub frame & cross member.
Cleaned out the power coating with the tap I guess.
George

[big iron]

George,
Do the 5/16-18 bolts fit tight in the holes? If the holes where drilled to .277/.281 as indicated I would think the bolts would be loose.
What do the holes measure now?
Bob

[BlackoutSteve]

5/16-18 thread (0.3125") will tap into a ~0.280" no problem. 

[NoYenko]

I was going threw some boxes today and came across the bag with my original AC shield bolts, cleaned them up & they are the same as my fuel line clip bolts #3958062.
These are the ones I took out because I bagged them. Wish I did that with all the bolts. Also they thread into the holes good not loose.
George

[mark x22]

Can you take a picture of the end ?

[NoYenko]

Mark, Here you go. Sorry for the wrong picture 10 posts back. George

[mark x22]

Thanks .