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Lightweight carbon wheel repair.
 

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greglepore
Joined: 10 Jan 2004
Posts: 1724
Location: SE Pa, USA

9/8/17 5:45 AM

Lightweight carbon wheel repair.

In the other thread about my c40 I posted about a pair of "cheap" Lightweight standard 3's that I picked up on another forum. I've been wanting to try either these or Mavic CCU's for a while, as they're renowned for a combination of lightness and unbelievable lateral stiffness while still riding ok. But the price of entry-usually north of 2k for Lightweights-put me off. These came up for $650 shipped, which is what the front alone would be worth if I couldn't fix the rear. It had failed in the "spokebed" -the strip of carbon where the spokes are bonded, but the wheel hadn't lost tension.



I used uni carbon for what would be a simple one layer repair-these wheels are only 1 layer of carbon to begin with, no need to overbuild. I cut a patch and slit it to go around the spoke. The wheel area was masked and sanded thru the clear to allow a good epoxy bond with the laminate.


I masked off the repair area so that resin wouldn't end up on areas of the wheel not needed.Mixed resin and hardener in a cup using a gram scale. Saturated the patch on a sheet of plastic, then picked it up and applied it over the area. I then covered it with a piece of polyethelyne (just a piece of baggie) as a release film (this is a subject in itself, but for quick and dirty repairs poly is fine, even kitchen film). You then apply pressure over the film - in production you vacuum bag, but for repair just about everyone uses masking tape, believe it or not. It allows plenty of pressure if you wrap tight.





Immediately after removal of the film, lots of excess epoxy. I over-saturated the small patch. Better too much than too little. Just made a little extra sanding work.

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After initial sanding.



This will get some additional sanding to feather. It looks much worse in the photo up close than it does on the wheel.The small voids will be feathered in and it will smooth out. After feathering, it will get a coat of clear, and then that will be sanded with 1500 or 2000 wet to feather it into the low gloss finish on the wheel. The repair is very strong, it doesn't look terrific in the photos, but it is a very small area. Larger areas would get a finish layer of weave-on most carbon parts the "weave" 3k or 12k area is a cosmetic layer, and the structure itself is usually plies of uni oriented appropriately to the stress. Small voids get filled with bodyfiller and sanded before paint. I didn't use a matching cosmetic layer here as the carbon/kevlar used by Lightweight isn't easy to match.

For perspective, here's a shot of the whole wheel. The repair is at 12.



Last edited by greglepore on 9/8/17 6:06 AM; edited 1 time in total

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Nick Payne
Joined: 10 Jan 2004
Posts: 2625
Location: Canberra, Australia

9/8/17 5:49 AM

If it doesn't work, you could always turn it into several coat hangers:

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dan emery
Joined: 11 Jan 2004
Posts: 6884
Location: Maine

9/8/17 6:21 AM

various

Greg, you are a man of many talents.

Nick, that is awesome - candidate for the world's most expensive coat hanger?

I'd like one for my $5000 suits (if I had any).

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Sparky
Joined: 08 Dec 2003
Posts: 19068
Location: PDX

9/8/17 1:48 PM

Spend less on bikes and you could afford them. No, don't. :)


Keep us posted as to the effectiveness of the repair.. Hope it holds, nice job..


Last edited by Sparky on 9/8/17 3:37 PM; edited 1 time in total

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sanrensho
Joined: 20 Feb 2004
Posts: 835
Location: North Vancouver

9/8/17 2:40 PM

Impressive and well done. Thanks for posting this.

Reading up, it seems that the LW wheels are a monocoque/one-piece construction like the Mad Fibers. Is the tension on the repaired spoke (bed) equal to the other spokes after the repair?

Or does the tension not matter, and the spoke simply needs to be anchored solidly?

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 5096
Location: Nashua, NH

9/10/17 8:32 AM

FWIW, when working with epoxy and fiberglass, I frequently use clear packing tape to apply pressure to a repaired area. It's much stronger than masking tape and can apply a good deal more pressure to help squeeze out excess resin.

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