Two part molded glass fender - not joined well

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PostPosted: Wed Aug 05, 2015 11:15 am
This fender was molded in two different molds and then "grafted" together. That's my term...maybe not the right term.
fender.JPG

PIC 1: The bottom edge of the fender. The nearest part to the road. There were some extended pieces molded out here, designed to be cut back to the shape that the end user desires. As you can see, once cut, it's pretty obvious that they didn't get enough glass or resin in this part. It's still sealed at the edges. For how long, I don't know. This dry/open pocket travels several inches back, especially along that crease where the filler portion meets the upper portion of the fender.
GLASS 2.JPG

PIC 2: From the center portion of one of the extended pieces where a hole was cut to add turn signals. Sealed at the outside edge, but they obviously did not use enough glass or resin to get this thing to be a solid piece.
GLASS 3.JPG



None of these problems were evident from the edges as supplied by the manufacturer. It wasn't until the parts were cut back somewhat that the air pockets were seen.

What say you? Is this inferior glass work? Would you accept it like this and move on? If so, what fix would you apply? Cram it full of glass and resin? Fill it with epoxy? Just cap it off with body filler?

Thanks for your thoughts.

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PostPosted: Wed Aug 05, 2015 5:34 pm
Okay, here's the deal.... what you are seeing is imperfections in what is called "flash molding" of parts. Flash molding became more popular after the introduction of sandable gel coats appeared back in the 1970s or so. Smaller molded pieces are indeed put into bigger molds and "flashed" together by adding resin/mat/cloth as needed at the joined areas. The problem most times is that the resins are being added on to already curing parts so bubbles will indeed appear. Another phenom. that appears is a a "shrink back" of parts after they are pulled from those molds causing edge seems to open up.

So what to do????..... Evey kit car I've worked on in the last 20 years or so has had these flash lines that need careful massaging. And, no, they are unavoidable in almost any aftermarket fiberglass part.... If you can identify "where" the flashing has been done the best thing is to take a moto-tool or grinder with burr style bit and open up these areas. I surface them with West System epoxy using one of their marine grade filler/thickeners. This makes a nice paste that fills in, builds strength, and should give you a surface density that is the equal of the surrounding fiberglass. I do not like using regular fiberglass resins in these areas because I think you need a stronger and stiffer bond. You can still go over these areas when done with any regular filler or poly putty and feather that out as needed.
One thing, do not be tempted to just use a body filler on those areas as they are not stable and, trust me on this, the shake of a bike will quickly open them all back up!
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PostPosted: Thu Aug 06, 2015 7:38 am
I want to make sure I'm understanding you. Are you saying to insert the bit INTO the open area between the molded pieces to rough it up as far back as I can so that the epoxy has something to grab on to...then cram the epoxy into the gap as much as possible?

I hope that's what you're saying.

Now...the section that is showing inside that turn signal hole. I'm thinking it won't really be a problem in the long run, as there are 4 bolts that actually hold the LED box to the fairing. I believe those bolts will hold it all together without issues.

You know, back in the late 80's I worked at a fiberglass mfg where we produced golf cart bodies, sleepers and wind jammers for big trucks, fire truck body panels and tanks, hearse body panels and lots of tanks for the oil industry. We did both mat and spray glass techniques. I was involved in all aspects of it. I even built and maintained some of the molds. But mostly I was in the "bodywork dept", where we would search for bubbles and imperfections. We'd grind them out or cut them out with a knife, fill, sand and prime.

We would have easily rejected this fender. No question. I'm really surprised to hear that this is pretty common these days.

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PostPosted: Thu Aug 06, 2015 7:49 am
Yeah, you got it with technique there.... And, yes, fiberglass work has deteriorated to this level now mostly because of imported stuff. Even the stuff that says "USA" on it may come here in pieces and be flashed together here so it can get that stamp, save freight costs on oversized pieces, etc. Go to any speed shop and take a good look at aftermarket hoods even by the biggest names in the business and you'll be shocked at what you see. Don't get me wrong there is still some excellent work being done by a few companies here in the US but there just aren't many now.
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PostPosted: Thu Aug 06, 2015 8:02 am
Thanks, sir. I think that fix won't be so bad after all.

I'm fairly certain that if we were going to "fix it" back at the old plant, we would have probably ground out the entire inside portion of that tire well, roughed up the remaining surface area, and laid in mat and resin. It wouldn't have had to been perfect since it's never going to be seen...just structurally sound.

But that does seem overkill in this instance. If the epoxy will stick, I like it. And it's a lot less itchy fix.

Thanks.

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PostPosted: Thu Aug 06, 2015 5:24 pm
Yeah, you were working in that "quality" era of fiberglass..... :( ...it's just not there much anymore. The epoxy will stick, just give it a nice rough surface to lock in and fill away.... The kit truck build I did had about 8 pounds of it in the flash seams.... Last simple aftermarket hood I did had about 1/2 pound of it.
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PostPosted: Fri Aug 07, 2015 7:07 am
I'm way too familiar with pneumatic grinders and 100+ degree heat with fiberglass dust stuck in every crevasse on the human body that can sweat.
:rolleyes:
Back in that time, my girlfriend refused to sleep in my bed. I had gotten so used to it that I really had no idea that my bed had any glass in it...but apparently it did.

Alright. Thanks for the poundage report. I was looking at it closer last night and noticed that I won't have any choice but to fill the turn signal hole problem as well - because it's all part of the exact same problem. Which is fine. There are only two bolts holding that turn signal in...so I wouldn't have felt comfortable anyway. And I was thinking I'm going to have to add a lot more resin to this thing than I had thought. I hadn't thought to weigh it before I filled it. I'll try to remember to. I don't imagine I'll be anywhere near those numbers, but it's hard to tell until I start pouring.

The bike owner ordered the West Systems stuff yesterday, so it will be a few days before I get to it.

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PostPosted: Fri Aug 07, 2015 7:09 am
I just want to add. You haven't really lived until you've hand rolled a freshly sprayed mold and had resin squirt up into your eyes as you're rolling into a tight corner.

Good times.

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PostPosted: Fri Aug 14, 2015 7:56 am
The original fender hung out and watched over this new process with great curiosity.
looking.JPG

The West Systems epoxy resin as suggested by DarrelK
west.JPG

We used some foil tape to try to block off all gaps in that turn signal hole which happened to fall right in the middle of this giant dry spot. Looking back, we should have just used a single piece of tape over both sides and let it fill up and recut the hole later. This tape leaked pretty badly, so we ended up having to contain it the best we could until it set - and then go back and fill it again. We didn't weigh the fender, but I think we used about 300 grams or so.
setup.JPG

We built a bit of a funnel with the aluminum tape at the big portion on the bottom of the fender well.
mpty.JPG

And....after the second filling, still had bubbles coming up where it was filling in the entire seam from where the inner piece was flashed onto the outer piece. There is probably a 2.5 ft seam in there that had to fill up before it would level off.
full.JPG

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PostPosted: Fri Aug 14, 2015 8:00 am
I left before the epoxy set up. I told my buddy to let it gel pretty solid and that he could probably take a razor and just zip off the excess that was built up on the funnel. He sent me these pics later last night. Looks like it'll do.

done1.JPG
done 2.JPG


Thanks for the advice on this, Darrel.

And now...back the to the other thread....and back to the sanding and priming. It'll never end.
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