CraigH

Interesting, so my 71 is May production if i recall correctly.

Is it likely a production change or its been swapped off a later model.

Do I need to handle the repair any differently ? Is it still polyester resin based ?

Alan 71

Hi Craig,
I'd expect to some fiber-glass stands and texture on the back side of the valance.
I didn't see any in the photos that show the back side of what you're working on.
Regards,
Alan





This might be an indication that it IS a GM panel.

CraigH

Good pick up Alan

It has the following in raised letters "CHEV 3977870"

The only place you see the fibres is where they have drilled the panel for bolts or clips.

caskiguy

Alans pretty amazing isn't he Craig ? Doesn't miss a thing, which is a great benefit to all of us.

CraigH

He certainly is.

I did a search on that part # 3977870 and it is the rear valance 71-73) but should it be prefixed by GM not Chev.

Don’t have access to many other Vette’s in those years near me to compare.

DUB

The part number cast into the part is not what I am worried about...because the molds could have been used with different materials.

I am guessing that when you grind into it it is a light gray color. IF it is and I am almost 100% positive that I am correct. If I am correct....then the polyester resin does not bond to SMC. it may seem that is does...but in time it can literally fall off. IF your part is an actual factory polyester press molded part...it will be a dark gray like Alans photo CLEARLY shows. Your part is more like the first photo in POST #1215 that you posted where I can see the quarter panel is a light gray color where you sanded back the paint..

I know many people use it...and will swear by it....but I also have worked on Corvette where polyester resin HAS been used on an SMC part and I can pop the laminated repair off easily with a screwdriver once I get under it.

This is when the WEST SYSTEMS epoxy resin ( part number 105) and hardener (part number 206) is what you need to use.

DUB

CraigH

Thanks Dub

It is very light grey when sanded.

I can source the West Epoxy and Resin in Queensland online so will order some today.

I assume everything else is the same matt, process etc.

Oh well one step forward and one back.

CraigH

I am a little confused...is it just the Filler panel that is SMC or are the rear guards and halo etc ?

I have repaired the front clip, doors and the rear wheel arch with polyester resin, glass etc. as I thought it was after 71 it changed to smc.

If the rear guards are smc also do I need to grind it all out and start again ?

CraigH

Done lots of searching tonight and I find that the 71 front clip through to doors should be ok with Polyester resin repairs as its not SMC

The rear quarters most likely are SMC.

Rear deck Halo etc are not SMC

And in my 71 the Rear Filler Panel is SMC.

Lots of conflicting info out there.

So I will order the West Systems Epoxy resin and Hardener.

To be safe should I grind out the rear arch repair and start again ? It seemed to laminate up fine but I don't want to risk it if it may delaminate later.

Am I making Sense DUB ?

CraigH

This is doing my head in

From reading the NCRS forums and others

Through the `68 model , the fiberglass was a polyester based product. That is generally known as FRP and is compatable with the commonly available liquid polyester resins that we have used forever. In `69 General Tire Co introduced a low shrink resin they called Genite. The first Genite panel was introduced on `69 doors during the production run. You will find some cars with one type on the right and the other on the left. More panels were introduced as they became available throughout `70 and `71. Then came the new SMC panels which were introduced in `71. The first SMC panel being used on `71 rear quarters. SMC panels were phased in through 73. The `74 body was the first to use all SMC components.

press molded polyester = (Genite)

So my 71 will be likely Genite panels except for the rear quarters and possibly tail light panel and rear valence.

My repairs to date have been with Polyester resin.

Should I grind out the rear quarter and tail panel repairs and start again ?

Alan 71

Hi Craig,
Here are the panels on mid-January 1971 assembled car.
You can see the where the materials were used.
The exhaust filler panel is the one that I posted photos of... not the first dark one (69), but the later photo.
Regards,
Alan

I don't know if you've seen these or not.

CraigH

Thanks Alan

From my reading the Genite "press moulded polyester" (with low shrink resin) will be a mix of medium and light grey and the SMC panels possibly possibly lighter.

The only bit that seems consistent in all the posts is that 71 will have SMC rear quarters and possibly rear tail light panels.

So my repairs on the rear quarter and tail light area need to be done in epoxy resin and the remainder polyester.

a bit of a pain but the grinder may be my friend for a while :-)

At least the front through doors is ok.

Alan 71

Hi Craig,
Finding things like this can be helpful. The tags are imbedded in the resin... you can't feel them.
This is on the underside of the hood surround in the top of the left front wheel well.
Regards,
Alan

PS.... I consider this as being part of 'matching numbers' !?!

CraigH

Hi Alan

Yes I saw a sticker similar to that on my original hood when i cleaned off the underside.

CraigH

Pictures from behind panels

The door


The rear tail light panel


Rear Quarter







Rear Deck



The quarters have a little less visible fiber than the others.

Not sure if that helps decide if they are SMC or press moulded polyester

caskiguy

Just curious, is there a way to "test the body panels to know what they are made of" or is it just by visual assessment ? Sorry to see this happening Craig but, I'll be in the same boat down the road and I wouldn't have a clue.

CraigH

So I almost had the filler panel finished



But given its SMC I decided to do it again so i went out and grabbed.



And some matching chopped fibre powder bound matt.

Then I took to my finished panel and ground out the new polyester resin filled glass on each side of each repair and then tried to break or delaminate the glass away. It took a pair of pliers and a lot of twisting and in the end it took away some of the SMC with it as well.

So it seems to have been fairly well stuck but over time who knows.

Then I ground it all out again and laid up the new epoxy based products to the inside.







Must say the epoxy compatible matt is so easy to use and I do like the extended dry time.

Lets see what its like tomorrow.

CraigH

Still would love some comments from the experts on the inside panel pictures as to if my rear quarters are SMC and the rear tail light panel.

Alan 71

Hi C,
Here are some photos.
At the fear of being yelled at I won't post what I think the material is.
Again, this is a mid-January 1971 assembled car. (6589)
Regards,
Alan

Underside rear deck:





Tail light panel:


underbody and quarter panel.

CraigH

Mine is early May 16432: May 6, 1971
Depends if smc started at beginning of 71 or mid production and was it just the quarters or the rear light panel as well