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Family Man

07 yz450f stall then hard to start when hot

57 posts in this topic

My bike started stalling on a long ride the other day. I recently had the valves replaced and the seats recut. Less than 5 hours ago. After the bike stall the bike is really hard to kick over, almost impossible. Then after afew kicks it would it would get easier to kick over and then start. did this multiple times. Babied it back to the truck. Do you think the valves are out of adjustment? I also installed a new timing chain, maybe it's bad?

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The bike was starting on the first kick two days prior. seemed to be running great. but I wasn't pushing the bike as hard for very long. Ill check the timing and the decompression linkage.

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Timing is dead on. the decompression looks to be working.

Im going to check the intake clearance.

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the left side/ shifter side exhaust valve clearance is .5mm and the right side exhaust clearance is .7mm.

Way too big. That will actually account for some of the hard to crank complaint, as it means that the valve lifter won't contact the decomp pin as soon as it should.

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yeah the manual say it should be between .2mm and .25mm right? How much oil should be on the cams, they look pretty dry?

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Ill go get some shims tomorrow. The book has a nice chart to show the needed shims once I take out the old shims my local mechanic should be able to get me the right shims.

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Loose clearance is less likely to keep it from starting than tight would, other than the effect on the decomp setup. Who originally set up the clearances, you or the machine shop? If they did it, did they do it with the head on a bench or bolted down?

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Something else just occurred to me. Valves don't get loose from wear, they get tight. Yours are too loose.

Notice that the left end of both cams has tighter clearance than the right, and in the case of the intake, each one to the right is looser the farther along you go?

Check your cam caps. You might have seized it.

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The machine shop shimmed the head for me... I have no Idea as to the method they used. The cam caps look kinda burred up on the edges. Havent taken the caps off yet but I will soon.

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I bet it seized up too. I borrowed a snap on torque wrench to torque the caps. Now I wonder if the wrench is out of calibration.

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Welp. You are right. It seized up. The cam cap bolts were finger tight, some of them even less. They may have loosend after the seize though the cams look dry to me like maybe the oil pump quit and the cams seized. the journals look trashed. most of the valve caps spin freely and look new. Im thinking the other two cam caps would spin too if the journals were deberred. Do you think the cams can be cleaned off since the head is softer than the cams? Im guessing most of the metal around the cams were they sit in journal comes off? Can the head be repaired? Do I have to split the cases to change the oil pump?

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Who originally set up the clearances, you or the machine shop? If they did it, did they do it with the head on a bench or bolted down?

Just out of curiosity...... Where would the difference be in checking/adjusting valves with the head on a bench versus tq'd down? As an example, is it similar to using a torque block when honing cylinders?

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Something like that, yes, but it normally makes very little difference to a YZF if the head's truly flat. I've only seen the clearances vary from bench to bolted down a couple of times. It can happen, though.

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