Dangerranger1973

13 yz450 intake cam

12 posts in this topic

I had an issue with the intake valve #2, closes to the chain back in October. The bucket stuck in the head and broke. I was able to take the head apart and fix it so the bucket would rotate freely and wasn't binding. I did notice that the intake cam was a little advanced compared to a 12 yz450.

So it ran great had a little rough idle but started and ran great. Went out Saturday and it slowly got harder to start and was kicking back on me quite a bit a couple times each time I would start it. The last time I went to start it it kicked back and then next kick locked up.

Got it back to camp and pulled the valve cover set the timing marks and now my intake cam is pointing straight up. It slipped on the gear about 45-60 degrees.

Any one see this issue

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I had an issue with the intake valve #2, closes to the chain back in October. The bucket stuck in the head and broke. I was able to take the head apart and fix it so the bucket would rotate freely and wasn't binding. I did notice that the intake cam was a little advanced compared to a 12 yz450.

So it ran great had a little rough idle but started and ran great. Went out Saturday and it slowly got harder to start and was kicking back on me quite a bit a couple times each time I would start it. The last time I went to start it it kicked back and then next kick locked up.

Got it back to camp and pulled the valve cover set the timing marks and now my intake cam is pointing straight up. It slipped on the gear about 45-60 degrees.

Any one see this issue

Sounds like your intake cam sprocket spun on the shaft. So you will need a new intake cam.

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The timing marks were found in their proper orientation when you took it apart for inspection?  Only the orientation of the lobes was off?

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Yes timing marks are still spot on the lobes are out of alignment by a lot I will pull it down tonight and take a picture.

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There's no mechanism I'm aware of by which the cam can slip ahead in the sprocket so that it becomes advanced.  What must have happened is that the cam sprocket spun most of a complete revolution over the camshaft, hard as that might be to believe.  Hard to believe no valves are bent, but maybe you got lucky. 

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So I got the valve cover off and I found that the timing marks are lined up. But here is were it gets weird. It has 2 dots on the cam gear and one was lined up so the cam has slipped in the gear or it jumped time and the cam shaft rotated in the advance direction 5 teeth and just happened to line up with the other timing mark. I have a brand new tensioner on it. I really dought it jumped timing and just happened to land on that spot.

image.jpeg

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Got the head off and the valve just nearly touched piston just a light mark in the carbon on the piston just got to see tomorrow if the valve is bent and not seating. Looks like the bucket stuck in the head again only 1.5hrs after I got it back together. The cams are still getting replaced. Going to hone the intake side cause the #1 valve bucket will not rotate in the bore.

What is my clearance on the valve bucket to cylinder bucket bore in the head.

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Ok got the head pulled apart and cleaned the bore with a cylinder hone. Got it all washed up and checked my bucket to cylinder clearance and the intake side is .002" on both and the exhaust side is .0005" on both.

What's the thoughts on the clearance should I be good or that's a little to much?

Valve is good also

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So I bolted the head down to check for warping and I noticed while checking the bucket if I put pressure on one way on the top of the bucket to simulate the cam pushing on one edge it will drag an edge up and down.

So my head is scrap unless anyone thinks and can be milled and then sleeved and bored to the bucket again.

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