Just how bad are replica fiberglass parts?

Anything goes in the world of fiberglass and plastic



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PostPosted: Sat Jan 02, 2021 9:15 pm
Hey guys, I'm interested in putting an overfender kit on my nissan 350z. The only kit I like is unfortunately discontinued and I can't find any second hand for the life of me. I need some input if it's a bad idea to deliberately purchase a crappy copy of an authentic fiberglass part with an attempt to just fab it until it works. I plan on molding them to my quarter panel and fender regardless so there will be fiberglass work involved even if I do get an authentic part. If anyone has experience with cheap replicas of overfenders and if they fit so horribly that they were unsymmetrical/ etc, your input is much appreciated!

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PostPosted: Sat Jan 02, 2021 10:59 pm
Man, it's just a mixed bag of quality out there on parts like this..... I am assuming almost everything that is out there for your car is coming from China, Malaysia, etc? I am also assuming that the Japanese stuff is probably just coming from China as well? I've always found American made stuff to be quite superior in thickness/construction but a lot of those companies don't want to fool with the import scene. You might see if some custom work would be available from some of those American companies. This is one I've sent some guys to in the past.... http://www.customcompositesok.com/ If you do a search other small companies that do both open lay ups and infusion molding should come up.
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PostPosted: Sun Jan 03, 2021 8:02 am
Most need a lot of 'massaging' to fit. Even more to fit very nicely. Had a 55 Chevy hood, with a scoop on it, I actually had to cut slits in the underside support, put a 2 x 4 against the center, and use ratcheting straps around it, to add more curvature to the hood, so it matched the cowl. Big, awkward job!
Most need a good blocking with 80 grit to flatten them, and then some Poly primer for some filling for a second blocking out.

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PostPosted: Sun Jan 03, 2021 8:35 am
chopolds wrote:Most need a good blocking with 80 grit to flatten them, and then some Poly primer for some filling for a second blocking out.


And they're the "good" ones.
Chris

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PostPosted: Sun Jan 03, 2021 9:57 am
There is another industry wide problem with a lot of these parts.... One word, DURAFLEX. I refuse to buy fiberglass parts that are made with the Duraflex process. The claims for this process are that it reduces shipping damages and is easier to work with. Well, for the manufacturer it's probably pretty great because the parts pop out of mold more easily because they can flex more without damage. The down side for the end user is sloppy part that will flex so much there is barely even a "starting point" for proper alignment. And wow, this stuff is so thin sometimes you can hold a panel up to the light and see through it!
When I had my C6 Corvette I picked up a damaged American made vented hood for a great price. Buddy of mine also was looking for a hood and went with a new Duraflex hood. My hood bolted directly in place with the gaps almost as good as my factory hood. His hood had a diagonal twist to it. He ended up making several kerf cuts, built a wood frame, and twisted it back, and applied more layering of fiberglass. I had about 5 hours of total body work in my hood (that included repairing the original damage from poor packing). He had at least 20 hours in his.....and worst of all he ended up with paint failure on the part about a year later. His hood had been made in two parts with a flash seam in the middle. He didn't notice this (probably the reason for the twist also) and had just primed over their primer and finished. Their were obviously air pockets down inside that flash seam so the paint itself started bubbling later......
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PostPosted: Mon Jan 04, 2021 2:37 am
DarrelK wrote:There is another industry wide problem with a lot of these parts.... One word, DURAFLEX. I refuse to buy fiberglass parts that are made with the Duraflex process. The claims for this process are that it reduces shipping damages and is easier to work with. Well, for the manufacturer it's probably pretty great because the parts pop out of mold more easily because they can flex more without damage. The down side for the end user is sloppy part that will flex so much there is barely even a "starting point" for proper alignment. And wow, this stuff is so thin sometimes you can hold a panel up to the light and see through it!
When I had my C6 Corvette I picked up a damaged American made vented hood for a great price. Buddy of mine also was looking for a hood and went with a new Duraflex hood. My hood bolted directly in place with the gaps almost as good as my factory hood. His hood had a diagonal twist to it. He ended up making several kerf cuts, built a wood frame, and twisted it back, and applied more layering of fiberglass. I had about 5 hours of total body work in my hood (that included repairing the original damage from poor packing). He had at least 20 hours in his.....and worst of all he ended up with paint failure on the part about a year later. His hood had been made in two parts with a flash seam in the middle. He didn't notice this (probably the reason for the twist also) and had just primed over their primer and finished. Their were obviously air pockets down inside that flash seam so the paint itself started bubbling later......

These are the fenders I'm looking at. https://www.ebay.com/itm/Nissan-Fairlad ... 1777010235 I'm almost certain they're of terrible quality, but they're the only overfenders I like and I figure making these fit would be easier than making ones from scratch custom to my liking.

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PostPosted: Mon Jan 04, 2021 9:24 am
Yeah, they are coming out of Malaysia so get ready for the bad. So they picture these as just screwing over top of the original fenders.....how were you thinking of attachment?
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PostPosted: Mon Jan 04, 2021 4:05 pm
DarrelK wrote:Yeah, they are coming out of Malaysia so get ready for the bad. So they picture these as just screwing over top of the original fenders.....how were you thinking of attachment?

I was planning on sanding the fenders underneath to bare metal then fiberglassing them on. I heard concrete adhesive like sikaflex is good as well, but I don't think the people going that route are going to mold theirs fluidly into the panel. I expect I'd need to reinforce the fenders on the backside with some more resin and mats.
Here's a link to the same product with some views from the rear, they're paper thin. https://www.ebay.com/itm/JDM-Star-Fende ... 4902.l9144

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PostPosted: Mon Jan 04, 2021 5:10 pm
Well, first.....those are horrible....that can't be more than a single layer of 4 ounce matt. My kit truck's bed quarters are bout 3 times that thickness. You'll have to layer those up with more matt and honestly it wouldn't hurt to bond some cloth over that. Problem is that your are going to have to watch about going to thick or they could "draw" and shrink up causing even more fitment problems.
Okay and here is somewhat of a problem. You are bonding two dissimilar materials here with different rates of contraction and expansion. Back when guys were first doing fender flares on Porsche Turbos you saw a lot of fiberglass flare kits. They hung around for a few years and then you saw guys buying metal flares. We even had a guy here in the Plastics section trying to do the fiberglass ones.... he never could get them stable and ended up selling the car. Between heat/cold cycling and the vibration that occurs at those edges it is just a recipe for cracking. I'd say there is a good reason that we see this type of cheap flare just screwed or riveted in place. Take a good look at almost any factory flare on a car, truck, etc., you will see screws, rivets, 3m two sided tape, but never an actual joining of any composite directly to steel or aluminum.
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PostPosted: Mon Jan 04, 2021 11:27 pm
DarrelK wrote:Well, first.....those are horrible....that can't be more than a single layer of 4 ounce matt. My kit truck's bed quarters are bout 3 times that thickness. You'll have to layer those up with more matt and honestly it wouldn't hurt to bond some cloth over that. Problem is that your are going to have to watch about going to thick or they could "draw" and shrink up causing even more fitment problems.
Okay and here is somewhat of a problem. You are bonding two dissimilar materials here with different rates of contraction and expansion. Back when guys were first doing fender flares on Porsche Turbos you saw a lot of fiberglass flare kits. They hung around for a few years and then you saw guys buying metal flares. We even had a guy here in the Plastics section trying to do the fiberglass ones.... he never could get them stable and ended up selling the car. Between heat/cold cycling and the vibration that occurs at those edges it is just a recipe for cracking. I'd say there is a good reason that we see this type of cheap flare just screwed or riveted in place. Take a good look at almost any factory flare on a car, truck, etc., you will see screws, rivets, 3m two sided tape, but never an actual joining of any composite directly to steel or aluminum.

I've seen it done before, https://www.instagram.com/p/BsO3w0gHCBL ... kqzwrrb7le
https://www.instagram.com/p/BpkQgE7nM63 ... ui2izb914t
might be too ambitious.
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