Finishing Up! - my Stumpjumper Carbon Frame Repair

(3rd in a series of 3)


Here is a quick look at the final steps in my carbon fiber frame repair job.

In the previous post, I explained how I epoxied 4 layers of carbon fiber cloth over the damaged area. After the final layer was fully cured, I started sanding things down again. Once the area was sufficiently smooth, I brushed on a final coat of epoxy and let that cure for 10 hours in my hot box (see previous post).

Once that final top coat of epoxy was cured, I started the sanding again: I used a little 80 grit, then 120 grit, then 220 grit, then 220 grit wet (pictured below), before finally buffing things out with some steel wool. It's pretty smooth and shiny at this point and my fingers are pretty sore.

Final wet sanding before the enamel clear coat

Next, several rattle-can coats of clear enamel. This stuff provides UV protection to the epoxy, which can yellow over time if exposed to UV. At this stage, I'm spraying beyond the repaired area onto the factory paint/finish, in order to help blend the areas together.

UV protection

After about 4 coats of enamel, it's time to polish so that the repaired area will have a shine similar to the factory finish. I rubbed this cheap stuff around for about 30 minutes before I thought things looked decent.

Polishing the finish; trying to blend it to the sheen of the original finish.

Comparo: the repaired stay is slightly 'fatter' (not much) and it's definitely stiffer feeling when gently applying pressure to the stays by hand.

Time to get it together!!!

My 3-year old got pretty worn out watching me build it back up. This was the most zen-like bike-building session I've ever experienced....since becoming a father.

Not your 'factory finish'.

I started by riding it around the yard, carefully watching and listening for issues. Then I eventually worked my way up to riding it down the concrete staircase in front of our house....expecting a spectacular crack & crash at any moment. So far so good....

The steed rides again!

I plan on carefully subjecting the rear triangle to more and more abuse at low speeds, until I'm confident enough to gradually work it up to race pace again!

Edit/update: I have now exposed the bike to several laps of normal aggressive riding on my local mtb trails and it's riding beautifully.

Stumpjumper Carbon Fiber Frame Repair

(2nd in a series of 3)

Trying to find materials was very daunting at first. It seemed like everywhere I looked online people were selling a minimum of 1 yard of carbon fiber cloth (in widths varying from 3'-5'). This is way more material than I needed and I figured that if I bought a yard of several different weaves, plus a peel-ply, and probably way more epoxy than I needed, I would probably be getting pretty close to 50% of the cost of a professional carbon bike frame repair (which seemed to run about $300).

Most of my supplies.

However, after much more searching, I found that US composites sold carbon fiber fabric "tape" (which just means that the widths are narrow....like, 3" to 6"). I ended up order the 12k cloth 6" wide by 2' long, plus a small (20 oz.) quantity of their epoxy resin and hardener. The total cost for these materials was $20 + shipping. I probably spent another $25 on other random materials (foam paint brushes, good electrical tape, clear coat spray, rubber gloves, etc.). I also bought some graphite powder, which I didn't end up using.

My "layup schedule": progressively wider swatches with alternating weave angles (0/90 degrees, 45/315 degrees), then a patch of old rip-stop nylon as my "peel ply", and finally a semi-rigid cardboard cut-out to help provide pressure on the chain stay's inboard side where the rectangular tube wall is a bit concave.

To figure out what sizes, shapes, weave orientation I would use, I started by cutting out a scrap piece of plastic and laying it across the repair area in various ways. Then, I used it as a pattern to cut the cloth. I'm a total newbie, so I have no real expertise in figuring out what is ideal. I searched a few forums and found myself looking down a very deep well of knowledge and theory about strand orientation and decided to go more with the 'gut-feeling' layup.

In preparation for the layup, I cut several lengths of Scotch Super 33 electrical tape and perforated them with many pinholes. This will allow the excess epoxy to seep out when tightly wrapped.

Perforated electrical tape (the premium stuff: 3M Super 33 for extra elasticity); this will serve to compress the layup schedule in lieu of a vacuum bagging set up.

For a job this small, not much epoxy is necessary. I mixed it in small batches. In the photo it's on a scale, but I ended up not measuring the parts by weight (since I was mixing such small amounts) - instead, I used the small measuring cap included with the bottle, measuring out 1 part hardener to 3 parts resin.

Mixing some epoxy: US Composites 365 system - 3:1 medium

I didn't take any photos mid-layup because it's a tacky mess that camera would not have survived. Basically, I just used my foam brush wet down each swatch of carbon fiber with the epoxy and then very carefully laid the wet swatch in its position on the frame. The 12k carbon fiber cloth I used isn't very supple...it doesn't lay down really easily, so I had to be extra patient with it and use the epoxy liberally. I laid three progressively larger swatches of  carbon fiber on the frame, alternating the weave orientation (0/90 degrees, 45/315 degrees). Once all three swatches were in place and relatively flat, I carefully covered it with the rip-stop nylon scrap and then started tightly wrapping the whole thing with my electrical tape.

After everything is set and taped, I made my own little hot box (light bulb + tin foil + plastic storage box = a constant 95 degrees). The layup sat like this for 10+ hours to cure.

After I had a layer of electrical tape wound around, I applied my semi-rigid cardboard braces, and taped a little more. I was mainly concerned that the inboard wall of the rectangular chain stay tube was vertical, or slightly concave, and would therefore not receive as much pressure from the electrical tape wrap. I knew that the rectangle's corners would receive a disproportionate amount of pressure. So in an attempt to more evenly distribute the tape-wrap's pressure, I added the cardboard.

95 & sunny: just right!

My home made hot box was keeping a consistent 95 degrees, which was just right for the epoxy system I was using. It sat at this temperature overnight.

After 10+ hours in the hot box, I was dying to see how things would look. Would my peel-ply layers come off or would I have to sand through them?

After curing, I was a little apprehensive about how well the tape would come off, but it was not difficult at all.

I was even more skeptical that the rip stop nylon would detach...but it came off just fine also.

The final layer of carbon fiber cloth.

After sanding the original 3-ply layup schedule, I decided a fourth & final layer was in order. I figured I could achieve a better aesthetic working with just one single layer. From the the previous layup I had seen how well electrical tape works as a peel-ply, so I didn't even bother with the rip-stop nylon on this one. I sanded the patch area smooth, wet it down with epoxy, wet down the carbon fiber cloth with epoxy

In my next post.....

I should just have to sand the whole area with progressively finer grits (down to wet-sanding / steel wool), and then apply some UV protective enamel and final finishing coats.


For next blog post, click here!

Carbon Fiber Mountain Bike Frame Repair

(1st in a series of 3)

Before last weekend, I was the proud owner of a carbon 2011 Specialized Stumpjumper Comp. Since last weekend, I have been the proud owner of a cracked carbon 2011 Specialized Stumpjumper Comp.

Since paying people to do things is expensive (in the short-term....perhaps wiser in the long-term), I'm going down the DIY road. I figured I might as well blog it, so that those other fools who follow in my footsteps might have a little more light on their path.

My Stumpjumper suffered a broken chain stay while riding it 'normally'. I didn't crash it, or smash it on my way through a rock garden. One moment I was riding fine, the next moment I had weird tire-rub and noise behind me. It's worth noting that the crack is only on the inside, top, and bottom faces of the rectangular chain stay 'tube'...there is no problem with the outside wall of it. It's also worth pointing out that the crack appears to have occurred in the exact same location where Specialized has a seam between two parts in their triple monocoque construction:

My chain stay broke right at their seam. Hmmm...coincidence? I don't think so.

I am aware that there are several professional carbon fiber repair service options in the area (apparently Matt Appleman offers top-notch service), which may be the right choice for some people, but this blog is intended for armatures who want to DIY (trusting our lives with our own shoddy repair jobs, no doubt!)

So, getting started.... Here is a general outline of the process that I anticipate. I will try to blog about each step along the way. I don't want to duplicate the vast amounts of instructional information and videos out there that already cover the basic process for carbon fiber repair. But just for posterity, here is the basic process:

1. Take a deep breath, make a plan, and gather supplies! 
2. Prep the surface by sanding. Get down through the top coats to the actual cloth; go deep enough in the damaged area remove damaged threads; prep an area at least 2" beyond the damage on all sides 
3. Prep materials and "layup schedule". Determine wight, weave, sequence, & number of carbon fiber layers, and stack with peel-ply, breather cloth, and vacuum bagging materials (if vacuum bagging). 
4. Apply layup, vacuum or tape, & allow to cure; ensure no wrinkling, bubbles, etc. 
5. Remove peel-ply and work on sanding smooth transition to unaltered frame. 
6. Finish. Apply UV protective clear coat(s), work down to a fine wet-sand, polish, apply final coats &/or paint.

I have already completed step #2 above, and the "gather supplies" part of step #1 is proving to be pretty difficult, without breaking the bank.

For next blog post click here!

DIY Fork Mount (for bike rack cheap-o's)

1) Go to your garage or LBS (local bike shop) to find a taco'ed bike wheel from which you can clip the hub. Make sure it fits the bike you intend to haul around on top of your car, and find a a quick release skewer that will fit.
2) You better take a break: this has been pretty strenuous so far. Have a refreshing beverage.
3) Get an angle grinder, metal file, gritty sand paper, or use your teeth to make flat spots on the hub where it will rest on the roof rack's cross-bars. If you have Yakima bars (round) instead of Thule (rectangular), then make your flat spots convex to roughly fit the radius of the bar.
4) Go to your garage or LHS (local hardware store) and pick up a U-bolt that will fit snugly over your hub and cross-bar. If the threaded portions of the U-bolt are too long, you can just hack them off with a saw at later.
5) Fasten the hub to your bars with the U-bolt, and tighten it down.
6) Throw your expensive carbon-fiber mountain bike up there.
7) Cruise down the interstate
8) Go back to where your bike fell off and pick up the pieces off the road.
8) Now, back at home, adjust your rear bar so that your bike's back wheel lands on/near it and then get a nylon strap to secure it.
9) Have another refreshing beverage and admire your work.

Refurbishing Leather Bicycle Saddle.

There is a fine line, with worn out leather bicycle saddles, between a fine "patina" and general dysfunction. This old saddle had crossed that line and was no longer usable: it broke the third time I rode it.

New leather bicycle saddles tend to start around $60 (the Brooks Titanium Swallow is $500), and I'm cheap, so I didn't want to spring for a new one. A plastic seat on this bike just didn't look right, so I decided to replace the leather. Here is what I did...

Here's the broken seat.

I pulled the old copper rivets out by unbending their back sides.

This is what the frame looks like without the leather on it. The leather gets stretched from back to front creating a sort of natural 'suspension' system.

Next, cut-out the new piece, using the old as a stencil. After a little investigation, I found that you probably want at least 8 oz. leather (this indicates how thick it is) as a minimum. 10 oz. leather is probably ideal. Most places aren't in the business of selling a single 6" x 12" piece of leather, but if you look around, you should be able to find the right seller, eventually.





Now lay the new leather over the frame and get it into position, making sure it's a good fit. Punch new holes in the leather to align with the holes in the frame (don't worry about prepping the three holes on the little front piece until you have the back part completely finished).







I found these #9 copper rivets at my local hardware store for $.27 each. I got larger washer that would slip all the way down the rivet (the #9 washer is made to stop just a fraction of the way down the tip of the rivet). Push the rivet through the leather & the hole in the metal frame, and then slip the washer on the back side.


Now it's a matter of peening the rivet (no photos for this part!). This just means that you smash the rivet's point with a hammer until it's all mushroomed and disfigured so that it won't & can't slip through the washer again, ever. It's a little tricky to peen the rivets with the seat's rails getting in your way, but you'll find the right combination of tools that were meant for something else, to make it work.



Here is the final result. NOTE: in order to keep the whole seat from flattening like a pancake, I punched a couple of holes in each of the sides and laced them together underneath. This gives the leather much better form & structure.

For more general information on leather bicycle saddles, check out Sheldon Brown's page
This old leather broke the third time I rode it, leaving me without a leather saddle.

Idle Air Control Valve Fix

My 1999 Subaru Legacy Brighton (2.2L EJ22 engine) had an issue with its idle air control valve/solenoid. Over the course of many months, I got a handful of CELs (check engine lights) with a code of P1507: "Idle Air Control System Malfunction". The first few times I just cleared the codes, after all, the car was running and idling smoothly. Eventually though, I decided it was time to address the issue.Simply replacing the IAC valve is quite expensive: for a factory part I'd have paid $350 for the part alone. A local parts store would charge about $180 for an aftermarket version.Most typically, the IAC valve just gets too fouled up with gunk and needs a good cleaning. Here's how to go about it:

Locate the idle air control valve. On a '99 Legacy 2.2L, it is on the driver's side of the throttle body. The factory part will have a blue sticker on it giving the part number (A33-661 R02).
The valve is held on by two screws which have a reputation for mushing to pieces under the force of a poorly placed screwdriver, so make sure you have the right size (use a flat-head, not phillip's) make sure you have a very firm grip and plenty of pressure on the screw head.

I found all kinds of black gunk on the tip of the valve. Before cleaning it off, leave it plugged in to its wiring harness and lay it on the engine in a place where you'll be able to see it from the driver's seat. Turn the ignition key to the 'on' position (not start): the tip of the valve should move in or out, and back again when you turn the key off. If you don't see any movement, then it's likely your valve it either way too gummed up or, worse, the electrical/mechanical components inside have failed. Either way, you'll want to clean it up and try again.
Before cleaning, I removed the rubber O-ring from the valve (you don't want the cleaning agents to degrade the rubber). Next I used carburetor cleaner, rags and Q-tips to thoroughly remove all deposits from the valve. In the process, the spring and seating parts came out of the solenoid - I'm not sure if that is supposed to happen, but I was able to put them back in without problems.

With the valve removed, I also cleaned the air passages in the throttle body which also had plenty of black gunk.
My IAC valve was shiny-clean, so I replaced the O-ring and plugged it back in to the wiring harness to test it. I turned the ignition to the on position and it appeared to move in & out much more freely than before.

After ensuring that all parts were clean and dry, I re-installed the valve. Also, ensure that you have correctly replaced the air box, and that all other air intake components you may have removed are tightly reconnected.

Voila - it again idles smoothly.

Typically, an IAC valve goes bad by fouling, like mine did. However, they can also fail electrically or mechanically. Check for voltage in the wiring harness and continuity between the pins on the solenoid itself. I rule out mechanical failure by cleaning thoroughly and observing actuation of the solenoid when turning the ignition to the 'on' position.