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By Darrell Holigan
1) Before pulling the cams, mark the cam chain at both camshafts AND at the crank. I was told to mark it at the crank, but neglected to. There's a good chance the chain will jump a tooth at the crank while it's slack, so if you don't mark it, the marks you made at the camshafts probably won't help and will just give you a false sense of confidence.
2) Don't apply tension with the tensioner, your finger, etc, while putting the camshafts back in. After discovering my marks were useless and unsucessfully trying to sight the shafts by eye, I picked up this incorrect tidbit of advice on some message board. The thought was that by applying tension to the chain, you could prevent the camshafts from rotating slightly and shifting the timing. The problem is, if you apply tension, the intake camshaft and rear half of the crank take up the slack and pull tight. Then, as your exhaust camshaft goes down into the head, the chain slacks and it jumps teeth.
4) Count the links between the camshafts before you start tightening things down. You can be one link too tight very easily and not realize it. You might not notice until you have everything back together and go to turn the timing rotor, only to find that the camshafts won't rotate because there's not enough slack between them. Really, count. It's very easy when you compare it to the time it takes to remove and torque down the cam cover.
3) Failing to properly mark the cam chain, you need to offset the cams so that they are advanced slightly when the rotor is at 1/4 TDC. This is because the cams drop slightly as they go into the head and depress the valves, which allows slack into the cam chain. This slack will eventually be picked up by the tensioner as you rotate the crankshaft by hand. However, as this happens, the crank will rotate but the camshafts will not. If they are aligned properly before you begin securing the cam cover, they will not be aligned once you are done. One tooth advanced for both the intake and exhaust should do it, at least on the 98 ZX6R.
5) Don't check the timing marks on the camshafts until the cam cover has been torqued down, the tensioner reinserted, and the engine rotated one revolution by hand. This is kinda the corollary to point 3. As you rotate the engine, the slack gets picked up by the tensioner, and changes the timing. If your timing is correct before you install the tensioner and rotate the engine, it probably won't be once you're done.
6) Take pictures of the cable routing on the valve cover before you take things apart. The job will take longer than you think, and you will forget how everything went back together. Then you will consult your service manual and will find that the tiny, blurry pictures are actually of a 95-97 ZX6R with the note (98-99 similar); similar yes, but they route the cables differently. I think they're all correct now. I haven't actually ridden it yet.
Other than that (I think the total number of times I torqued down and undid the cam cover was somewhere between 10 and 15), everything went smoothly, thanks to those in here who gave me advice, you definitely saved me some additional pain. One recurring nightmare through the whole thing was that I would get the camshafts back in and the valve lash would be off; fortunately that was not the case. All valves are now in spec, biased towards the loose end. With any luck, it'll be a while before they need adjusting again.
Now it's time for a carb sync and an oil change, and I'm ready for spring!
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