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04 won't start, sunk exhaust shim?

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Can't get my 04 started. Have spark and gas. Checked the valves and the left exhaust shim was lower than the retainer. Is this a possibility? It is impossible to get an actual reading, since the gauge will hit the retainer before it ever touches the shim. New to me bike, had it at the track once, and it was progressively harder to start. Now impossible. Should I start by flushing out that shim and measuring from there, our just go straight for a shop?

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Yes, shim it. Im not a fan of any shop, unless they are truly pro's or your related to them. The exhaust side is so easy to shim, you dont even need to remove the cam.

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So just to be clear, it IS unusual for the exhaust shim to be lower than the retainer? I just want to be clear, this is my first bucket shim single. I have a decent amount of engine knowledge in general, and this is the only oddball thing that stuck out to me. I just wanted to hear from other CRF techs whether or not this is a clear red flag, and if anything other than a failed previous shim job could have caused it (valve stem sinking a small amount at the retainer doesn't make much sense to me without keeper failure). And to do the exhaust, all I need to do is slide out the shaft for the rocker, not remove the cam? The intakes were 004 and 006, and the other exhaust was 012.

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I can't tell you if its common, but exhaust problems are rare. Yes, you don't need to remove the cam. Look in the FAQ, think there's a video there too. Its painfully easy.

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On the clutch side there's a silver Philips plug, the rocket shaft slides through that. You do need to remove the 2 cam cap bolts, those bolts go through that shaft.

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I've already reshimed the intakes, it is just nice to hear I don't need to pull the cam again for the exhaust. My process for shimming that exhaust will be taking my depth gauge, measuring the recess, adding that to the shim and dropping a new one in, attempting to flush out the retainer so I can get a reading rocker to shim. Then shimming regularly from there. Does this seem unusual to anyone?

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I'm not sure, got this bike recently. However, it does have a sticker from a local shop on the head, and the previous owner thought it had been redone there (a friend was borrowing the bike and had the work done).

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Were the intakes zero'd, or the right intake zero'd? If so, and do some research here...the intakes dont last once they move. Mine were zero'd on an 05 I just got, shimmed them both and the right re-zero'd in less than 2 hours. Clean air and oil is HUGE on these bikes.

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Normally, the shims sit just a hair higher than the top. I'd be willing to bet that some cut the exhaust valve seats and that's the reason for such a thin shim. Like mentioned, the exhaust valves are pretty much maintenance free with little to no issues.

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