VikingTrad3r

most recent edit. just go to post 19 to see what actually worked.


****EDIT. the melted acrylic looked amazing, but was not able to handle the expansion and contraction forces overnight as the top heated and cooled. the gap reopened. read below to how i got to a permanent fix***

Edit September 2016: the final repair with job weld and screws is still holding up. The paint job never looked right because when the unit expands it reveals the unpainted plexiglass shows up around the edge. We didn't want to take the frame off because we couldn't find a clear step by step and dint want to risk ending up with no roof. At the time, 1500 (we are in canada) was too much to spend on a roof. We then bought a cracked targa top off a guy for 35$. We just did the same repair but we did the repair from the bottom which left the top looking very good. So we are back to a clear roof, repaired using job weld and screws as pins. For details go through thread.


Hi all,

My 85 had a cracked targa top that was about 1/8th inch apart at the frame and tight at the toe or leading part of the crack that is propogating across the roof.

So far, the repair has worked and we tried to make it fail by taking it on roads at high speed and slow speed that would challenge the integrity of the repair jo

b.

The research i conducted on how to repair cracked acryllic plexiglass lead me to the fish tank industry where there is lots of youtube videos showing how plexiglass is put together and repaired if cracked.

You will need:
1. piece of plexiglass, i got a peice of broken plexiglass from micaels craft store in the framing department for free. you only need the size of a quarter at 1/4 inch thick ish.
2. acetone
3. glass jar or something like it that resists acetone
3. pipette or dropper or needle or syringe that lets you place a droplet of acetone in a precise fashion and control the amount that comes out.
4. watch a couple youtube videos on repairing acryllic plexiglass


A) put a chunk of plexiglass (quarter sized about 1/4 thick) into glass jar, and put in enough acetone to cover it twice high. cover the jar.
let sit for a while, like 2 days. the acetone is going to melt the plexiglass and you will end up with a sticky goop. when this goop dries, it will be optically clear and just as strong as plexiglass....it will be plexiglass...in the shape of the bottom of the jar..



B) drilled a hole at end of the crack. u will notice that i have two holes. i messed up and drilled the hole before the end of the crack. look through the bottom of the roof at a bright light to make sure you are at the end of the crack when you drill. i used a 1/8th bit.

C) If your crack is tight, no gap, then your liquid plexiglass needs to be very runny. like water. get some into your dispenser and SLOWLY place a drop onto the crack and let the crack suck in the watery mixture. walk away. you should be good after this one application. let it sit for a few days.

D) you will still have a hole in your roof to deal with, and for those who have some gaping in the crack, you will need to let some of the liquid evaporate off so that it becomes a bit more syrupy. that said, syrupy is too thick as it will retain bubbles. somewhere between syrup and water. SLOWLY fill the crack, just let the liquid flow into the gap. It took me 4 applications before the crack was filled. Same with the hole. If you put it on too thick, then it will have bubbles that cannot rise up and pop and you will have a week repair job. Use a mixture that is as watery as possible while still sticking to the walls of the crack.

E) after its done, you will want to sand off the plexiglass that has built up. If you have been precise and not over applied, you shoul dhave minimal buildup on the sides. I learned this the hard way and now that I have a nice solid repair job I am sanding it and filling in the ripples so they cannot be seen.

F) then you paint the top, or apply carbon fiber as has been done excellently by two members of this forum. Pictures of both are in this thread here one red, and one carbon fiber. IF THE CRACK IS THIN and if you have done a great job on the repair, it will be optically clear and you would be able to use a 3m headlight repair kit on your entire targa top and it would be smooth and not really noticable. you might not have to paint or cover with carbon fiber.

In my case, the targa top must have come off while the previous owner was on the highway cause it had a lot of deep gouges in addition to the crack. So we painted to match our car color which in our case is torch red and we used a spray bomb of duplicolor crack fill primer with duplicolor torch red with 50% overlap and its looking good so far. we are using spray max 2k clear coat after its all done and im sure it will look excellent as we are wet sanding and doing it right.

Or you could buy a new one for a few hundred dollars plus shipping.

For us, its been 50$ in paint.

the crack is fixed, but i have not finished sanding and filling the ripple marks.

here are pictures. good luck if you want to try it. if you have a crack and want to repair, using the carbon fiber wrap would be an excellent way to get the integrity of the crack taken care of and then also cover it up easy and quick. personally i like the look of the red top on the red car so thats why we went with it. It will look like a fiberglass top when done.

VikingTrad3r

sorry guys. comp died ill try to upload from phone.

VikingTrad3r

edit: no the crack did not hold. keep reading.

obviously, i am not done on the paint. now that we know the crack held, im sanding and filling the ripples of acrylic that u can see. then clearcoating with spraymax 2k clear.

ill post a final poc of that but this is more focused on HOW TO REPAIR A CRACK. its held so far. we even took it up and down the curb to get the body to flex. we tried to make it crack. it held.

playsdixie

lots of threads on this lately...I used JB weld black to fill in the crack on mine....originally covered it with carbon vinyl but later painted it....have had no problems with it at all

VikingTrad3r

yes yours was one i was referring to. i didnt know u had used jb weld. i think that is an epoxy? from my research it showed that the only way to "chemically weld" to acryllic was to use acryllic in acetone or there is another way to do it with another chemical that i cannot temember the name of but i had the acetone on hand.

its great that jb weld appears to be an option because my method was long and very involved!

Vinfire

I had someone try to pry my top off i ended up getting new one on ebay but i would love to have a spare. How do i use the carbon fiber if you want i can include pictures of the crack its at the back (trunk)side i have all the pieces to put on and then i thought i d put carbon fiber on top?

VikingTrad3r

show me pics and i'll see if I can tell if it could be fxed with this method.

playsdixie

it's been almost a year for the jb weld black..no issues at all....I did sand it smooth before putting the carbon fiber on it....not a hard job for the targa...lots of internet video's on how to....

Vinfire

ok ill get pics to you tomorrow

VikingTrad3r

I am back to report on this....

it looks like the crack in this 85 roof was either caused by, or exacerbated by, thermal expansion and contraction.

Because while my repair and paint job was amazing and looked top class, the repair job cracked the very first night it was outside in the cold (went below freezing) and the crack opened up. Then when it warmed up in the daytime, the crack closed up. But ofcourse the paint now had a crack in it.

So I decided to sand it down again and this time use JB weld. And I put in two "teeth" on either side of the original crack so that the layer of jb weld was notched into the plexiglass in order to hold it from spreading again.

Got that all done, left it outside last night. again...SLIGHT shrinkage in the cold.

It cracks right at the aluminum rail, where there is no jb weld under the frame because i couldn't get in there.

So now I have many hours into this thing and I refuse to give up on it. there must be a way to repair this thing and have it stop spreading/contracting with temp fluxuations.

I am thinking I will have to remove the glass from the frame and complete the jb weld repair all the way down to the edge of the glass edge that is within the frame.

I have researched on this forum and I cannot find anybody who has documented themselves removing the glass from the frame.

anybody? heat gun?

Hot Rod Roy

Do a search on: Betaseal U-418 Look at the thread by Radio Joe, entitled: Top Repair Advice.

I did my top in about 2009 or 2010, and it's doing just fine!

(Where's the knock-on-wood emoticon?)

VikingTrad3r

Thank you very much for that!

for others who might be looking here is the link:
https://www.corvetteforum.com/forums...ir-advice.html

I do have the acryllic top but i think im going to have to do this because i really do not want to spend 800 plush shipping on a new top. i'll pull it off and get er done with pictures for all to see.

thanks again.

VikingTrad3r

ok i know there is a group here who would just buy a new top.....but for those of trying to save the bucks, i had to update because my first post would lead people astray. actually i should delete the info in those upper posts so others dont waste thier time.

in the end, the expansion and contraction is a very formidable force and even jb weld by itself in a 1 inch thick (with crack in the midle of that inch, so a half inch either side) gouged out with a dremel then filled in with the original metal jb weld wouldnt hold. it would crack it as shrunk in the cold and then close up when heat expanded again. leaving a crack. see pic.

in the end i got my dremel with a grinding stone and ground a huge area of the acryllic top away on either side of the crack. then i coated it all with jb weld, then laid fiberglass matt and pushed it down into the jb weld. then added more of the jb weld on top of the fibrglass matt so the mat was totally saturated and no air bubbles.


this was on the top.


then on the bottom, i tried a different tack. i cut two long deck screws using boltcutters so i had a small rod, or pin. i dremeled two grooves deep enough in the acryllic that the pins would be fully in the acryllic. i filled the two grooves with jbweld then gingerly set the screw pins into the grooves that were oriented perpendicular to the crack. they suck into the jb weld, no air pockets. i chose this method on the bottom because i dont want to have to repaint the underside of the top. i can live with these two pin repair marks.

so, if you find yourself with a crack that is expanding and contracting and u find jbweld needs something in it to hold tensile strength, this has worked me.

note i never did take the frame off. really didnt want to do that. when i repaint (using duplicolr spray bomb torch red match) and 2k clear in a rattle can i will repost finished product.











here is the crack opening after the jbweld repair with no fiberglass and pin screws as tensile strength boosters.





u can see what i did here on the underside.

VikingTrad3r

Just reporting back for anybody who finds this in the future. my final attempt with the screws and jbweld has worked great. through below freezing to rediculously hot and over many bumps. its held. everything failed prior to this. The only downside is you will have to paint your top or carbon fiber it as mentioned by another member.

if you want, you can get the duplicolor match, and givr. you will need some stretchy vinyl tape, sand it, some 3m plastic adhesion promotor, and some 2k clear coat to get a professional clear coat.

fwiw, if you are trying to save the 1K to get a new top, its worth it to pay a guy to paint and clear the top for you, probably not muchmoney. you can prepare it yourself and take it to him ready for paint. using spray bombs is very hard to get a finish that is not "striped" in the right light.

anyway, good luck all. i wish these lids were less money!

colter

With it cold i.e. crack opened up. Why don't you try filling the crack with something like Permatex Plastic Weld? You can get it in black. It's a two part structural type epoxy for gluing plastic, but can also gap fill.

Other thing to look at that is probably better is something like Weld-On #40. Which is a two part acrylic glue. You can tape off around the crack to keep the glue contained. Fill up the crack with glue. After the glue is set, you could try sanding it down smooth.

hotrodbob01

There is an epoxy adhesive used to attach body panels rather then welding. It is an extremely tough compound available at autobody supply stores. Once cured it is almost impossible to separate the replacement panel from the main body. It might be worth a try.

http://www.autobodytoolmart.com/3m-s...1-p-10380.aspx

CMiller95

How well did the acetone and acrylic wind up working?

VikingTrad3r

It didnt hold.


look up at post 14 and i explain what i did that has been a permanent solution.

cheers. VT.

VikingTrad3r

I'm revisiting this thread because this cracked targa top issue is so huge and given that these cars cost as low as 2k it makes no sense for some of us to buy a new 1500 roof. There are new panels to buy for $400, and you can take apart the frame and get the right adhesive. If I was in the USA that's what I would have done but for me it's just too much $ with shipping and freight.

So, after success with the first roof, which was butchered from the top down, meaning if sanded and bonds filled and laid fibreglass across the crack, and then had to go to the underside to add cut screws as pins that would 'lock' in the jbweld adding tensile strength.....

I decided to buy a new cracked targa top for $35. It's crack was very long!!! My first roof, the now red one, it's crack was maybe 20 cm or 5 inches and it was from the left side towards the centre. This new roof I picked up has a crack that is over 1foot long and is from the leading edge towards the centre.

I wanted an oem looking roof and wanted the translucent top again!

Here is what I did:

Flipped the top over and ground out a nice 1cm / 3/8 inch groove over the crack with a Drexel and the cylinder grinding tool. Use a utility nice or similar thin and sharp blade to remove any loose shavings. You need all the with flakes removed before the jbweld goes in.

Switched to the cone shaped grinding tool and then made 9 cross grooves perpendicular to the crack. These are almost as deep as my screws were in diameter, this repair is on the underside so you are going to see the frakenstein type mark on the underside but you will not see it on the top at all if you do it right. So don't go through the roof with the grinder!!!! Grind past the end point of the crack. And pout a cross pin groove just past or over the leading point of the crack.

Now cut the screws. Mine were about 1 inch long. Get the vacuum and clean up the mess.

Place the screws into the cross grooves and just make sure they are long enough.

Now you need 4 stacks of books or in my cause I used 4 jack stands with rags wrapped over the top so as not to scratch the roof. It's got to be high enough off the ground so you can get your head under and see the top if the roof. I laid on the ground.

Grab some heavy items and place them on the bottom of the roof (which is facing up) and far enough from the crack so that you will still have room to work on the crack with these weights sitting on the roof. I used random boxes of screws. I didn't need much weight.

The weight is to get the crack level on the top of the roof. Run you fingers over the crack on the top side (which is facing down) and get it even.

Now grab your scotch tape. Packing tape would probably work too, don't use masking tape.

Tape over the crack on the top side of the roof. Which is facing the floor.

Grab your syringe. Mix the job weld. I mixed an entire kit of jbweld. Do not used the quick set. I considered using the clear stuff because it claims to have a higher tensile strength than the original grey blend but I couldn't afford to have this go wrong so I stuck with the same stuff that worked for the first top I did.

Suck some up the syringe and push it into the crack. Think like air and do it in a way that would let the air escape. Slight angle, and from the bottom up. In my case this second roof I did the crack went under the front plastic part. I used the syringe to push hhhaaarrrdddd under that piece so that I could see the jbweld fill the crack from the underside through the tape. Shinning a light down helps see this I used my iPhone light. Drop your pins into the jbweld and roll them to coat them. I used a set of old needle nose to drop them into place and a piece of wood about a Popsicle stick size and pushed them into the groove. Then I gobbed more jb weld onto the suture so it's nice and thick.

Have a look underneath for air bubbles.

Let it sit for 24 Hrs.

Peel tape off and you will probably have a few small bubbles. I did. But I wasn't careful about how I pushed the jbweld in.

I used a pick tip and put a very very. Very smal amount of fresh jb weld into the air bubbles. (On the top side now btw).

Just put a very small amount in and let it slowly settle to its level. Then I put it into the hot sun. Any left over air will make these little bubble fills bubble up. I left it I to the sun for about 5 min. Then I took into the cool shop. The bubble collapsed and I have a perfectly smooth surface. Let that sit for 24hrs.

Grab your black sharpie pen. Colour the grey jbweld black.

Admire your work from the top. You will be barely able to see it.

From the bottom it is a different story. Frankenstein. I'll come back in a sec and upload some pics.

^^^ this seems like a lot of work but it is actually quite easy. The amount of work time doing something is about 1.5 hrs.

VikingTrad3r

pick the white stuff out