Making Lemonade... Look KG 381i

zerogravitas

Retro Guru
I am a big fan of bonded lugged frames (see my Vitus 992 build here) and I have always wanted a Look bike. Their early 2000s top end frames approach the pinnacle of this method of frame building and I felt one would fit well in my collection. I put up a wanted ad up here and was super happy to quickly agree a trade for a KG 381i. Sadly, when the frame arrived, it was badly packed in a flimsy box and the frame had been cracked at the driveside seatstay. I was gutted, and then to compound this the member I bought it off vanished and did not respond to any messages.

After getting over my irritation with the whole situation, I resolved to make a positive out of the problem, and learn some carbon repair before building up the bike as I intended.

So here goes. 😋

Here's a 2003 Look catalogue page showing the KG381i.

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Here is my frame - I have the Credit Agricole team edition at the bottom of the page, in size 57. The 'i' in 381i stands for integrated, as in integrated headset.

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The finish is excellent and the way each carbon tube is individually tapered and profiled makes for a really interesting looking frame. The lugs and dropouts are all aluminium, bonded onto the carbon. Some of the tube/lug transitions are filled over to provide a smooth joint. These frames are known for paint cracking problems at these points and mine sadly exhibits this at the seat tube/bb joint; something I'll have to do a little filling and retouching to sort out. There are some other blemishes in the lacquer which should be pretty easy to sort, but another issue is some bubbling under the toptube/headtube lug. This is galvanic corrosion of the alu lug pushing the paint up. I will have a think about what to do about this.
The geometry with flat top tube makes for a classy looking bike in my opinion. The rear dropouts are moveable to give options for handling, and the seatpost clamp arrangement is a clever wedge system. These frames all take a 25mm post which makes sourcing replacement posts an expensive faff though.

Here is the damaged stay.. not cracked all the way through, but about 2/3 around. It opens up a tiny bit when I put my weight on the dropout.

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First job was to strip all the bolts, adjusters and removable components off ready for cleaning and repair.

The final problem I have is the LDS4 fork that came with the frame was not original, and also has a larger crown area so doesn't blend well with the headtube shape. The original HSC4 fork would have been painted with a red/white fade to match the rest of the bike. Getting a 20+ year old matching fork with the right length steerer for me was going to be a challenge, so I have sourced a slightly newer HSC5 SL fork in bare carbon/black. It is an almost identical shape that keeps the silhouette of the frame looking correct and saves a few grams as well.

Watch this space for carbon repair progress, then when that is done and the paint fixed I'll move onto a build over winter. :)
 
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First up I had to identify the extent of the issue.

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I marked up the visible crack, then sanded the paint off in this area.

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I use a microscope at work, so used it to check the crack and took this quick picture that shows how it wraps round the stay.

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When I had done the investigative work, I used a Dremel and file to grind down the carbon of the stay. I will make the repair as a 'bandage' that wraps the stay, but I want it to be flush with the rest of the stay. I tapered it down to the crack area - by reducing the diameter I can wrap, cure and then sand the repair back before making good the paint. Removing as much carbon where the crack is will allow more layers of new carbon and a stronger repair. I sanded off the paint on the inner face of the stay, but left the carbon intact where it is still continuous.

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Looks a bit rough and ready here; I made it a bit smoother after this image, and then cleaned it all with isopropyl alcohol ready for the fix.
More soon . 😋

PS- @moonlite - I enjoyed your city cyclist photo series!
 
So here's how the fix went down - Sorry for the lack of a full photo of each stage, the sticky epoxy stage isn't ideal for stopping for pics!

I bought this kit from EasyComposites. Having used them professionally for a number of years, I highly recommend them for composites, resins, casting supplies etc. They have great customer service and some excellent how-to videos.
I roughly followed the bandage method they recommend for fishing pole repair, see here for a good Youtube guide;


Instead of just wrapping on top I reduced the diameter of the existing stay, as detailed above.

After cleaning my prepared surface with isopropyl alcohol, I cut a long CF ribbon bandage to width and wetted it with the supplied epoxy. Working time is quite short so you have to be prepared! I then applied the bandage, wrapping it firmly onto the existing surface.

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When I had achieved the right thickness, I used the supplied release film to wrap over the top, and then used masking tape to tightly bind the repair on whilst it cured. I also poked some holes in the tape to release excess resin.

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I let it cure overnight, then removed all the tape and film. This is how it looked after an initial sanding pass.

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I then wrapped the good section of the stay in fabric tape so I could use the surfaces as a sanding guide, taking back the repair to match the shape of the stay. It is flat on the inner/wheel side, with a rounded outside so a bit fiddly to match. Its gone well so far though! Most importantly the repair feels super solid. :p
 
Did a bit more sanding and put some primer over it.

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I used the other stay as a datum to guide some of my sanding, so protected it with more of the thick tape.

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Here's the little sketch I did to think through and illustrate my plan for the repair.
 
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