Friday, April 10, 2015

The art of the worst case scenario

When bikes come in for extensive work, the technician has to think what would be the worst thing that could go wrong. What would make this bike not worth fixing? Find it now, before you've invested a lot of your time to fix all the obvious stuff.

You cannot win them all. A lot of the time, the killer flaw only shows up when you're doing one last value-added thing that might not even have been on the original work request. Sometimes it's curable if you do everything just right. Sometimes it just looks curable long enough to lure you into another expensive round of heroic measures. Or you decide to break even or take a loss just to save the bike and spare the owner, because backing out would mean the shop got nothing and the customer left with a carcass.

Older bikes present the biggest challenge. Really primitive bikes are easy enough to fix, because from the late 1970s through the end of the 1980s, certain basic dimensions were standard enough to allow a lot of flexibility improvising solutions. With the onset of tightly indexed shifting and complex suspension systems, that all changed.

Check the obvious things first: look for cracks in frame, forks, rims and hub flanges. Wheels can be repaired or replaced, so then it depends on whether the customer is willing to invest. But frame cracks are a killer. Fork problems may be.

This week's geriatric bike was a turn of the century Cannondale F600. The owner has had it maintained carefully. It has wear, but no abuse. I've tuned it enough times to make the job almost automatic. Bearings that were properly adjusted at the beginning do not come loose. They call those things on the axles lock nuts for a reason, people. And they work.

The bike needed disc brake pads. It needed a chain and cassette. Those bumped the price up, but they're routine wear items. I did take time fooling around with some ideas for additional in-line brake adjusters, but ultimately went with a standard setup because extra adjusters provided no advantage. Disc brake manufacturers tell you to take up slack with the threaded adjusters so you don't remove brake arm travel on a cable disc brake, but winding out the adjuster removes brake arm travel. So screw it. I just snug it up at the brake arm to get the lever feel I want with new pads. Same diff, honestly. I'll add a little with the adjusters, but I won't wind them way out.

So...everything was done. I know this guy has his own shock pump, but I figured he might assume we had checked and topped things up. While the front wheel was out anyway, I put our shock pump on the Schrader valve under the fork crown on the Super Fatty Ultra fork.

The gauge read about 125. I figured I'd give it a couple of psi more, if only to cover the little "pssht" when I took the pump off. Supposedly the pump has an anti-bleed adapter, but what's a couple of psi among friends? I pushed the plunger of the pump. I heard a sharp hiss and the pump head jerked down on the valve threads. Did I not have it threaded on right? I turned it, felt it start to tighten and then loosen abruptly.

Another couple of test pumps showed that the valve stem would not hold either of our shop pumps. The threads had oxidized over the years and crumbled away enough that the stem was not obviously stripped, but it was skinnier than it used to be.

In bike suspension years, this thing is prehistoric. We're not talking Rockshox RS-1 Precambrian, but solidly Mesozoic. I have some Cannondale Headshok parts and tools from close to that era, but the manuals quite pointedly don't tell you how to jack together a mixed bag of parts from similar assemblies to try to keep a fork working at least ten years after the company wanted you to trade the whole bike in for their new and improved model.

This is the point where you back away slowly and try not to rile it up. I looked at a few procedures in case I needed to try grafting in an air cap from a different cartridge, but I really didn't -- and don't -- want to go inside the fork. Especially with obsolete assemblies you can take something that more or less works and turn it into a jumbled mass of oozing junk. Rider has no bike. Shop makes no money. Grief and wailing all around.

With the Cannondale we have a couple of options. The easiest will be to put in adapters and fit up a 1 1/8-inch fork. The customer also said he might just get a new bike. Meanwhile, he still has this one, just about fully functional. His shock pump, less used than ours, stays on the valve stem, he said. And when it no longer does, he's prepared for what he will have to do.

It does not always go this well. I won't bother to share all the death-on-the-operating-table stories I've experienced over the years. The point is that you have to try to think of that one worst thing. And you want to try to do it without becoming cynical. But better to be cynical than to lose the ability to find the flaws before they make themselves obvious catastrophically.

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