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2000 XR250R - camshaft to sprocket - which way around?

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Anyone know which way around the cam shaft goes to the sprocket? It would seem that I marked the sprocket to the chains position, but not to the camshaft for some strange reason (stupid me).

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There's a marking of a 7 or something similair on the cam shaft:

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Looking at the discolouration/dirt/markings, I think it goes this way:

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I know which way around the sprocket goes, I.e. Which side of the sprocket goes towards the camshaft, which side faces out. My question is for which of the two holes lines up with which threaded hole in the camshaft. If I put it the wrong way around then the cam shaft would be 180* out!

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XR motors cant be 180 out because they fire on every crank rotation. It'll work either way!

So if it fires once every crank rotation, then how can it not be 180* out? It's two cam rotations to a crank rotation isn't it?

The timing or something would surely have to be out. Because the cam sprocket has markings on it for TDC two horizontal lines and a vertical line that points upwards. The cam lobes point one way, depending on which bolt holes in the sprocket and cam shaft are out would depend on which position the lobes are pointing at TDC.

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1- So if it fires once every crank rotation, then how can it not be 180* out? It's two cam rotations to a crank rotation isn't it?

2- The timing or something would surely have to be out. Because the cam sprocket has markings on it for TDC two horizontal lines and a vertical line that points upwards. The cam lobes point one way, depending on which bolt holes in the sprocket and cam shaft are out would depend on which position the lobes are pointing at TDC.

1- The cam rotates once every two crank rotations.

2- either way will work. the horizontal lines will still be inline with the head surface at tdc either way.

The only difference is that the vertical line will be in a different location

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coopz is right,its a wasted spark type ignition,fires on a compression and exhaust stroke,

for reassembly its easier with the cam lobes pointing down ,but so long as your at tdc and the sprocket lines line up across the top of the head , your good to go

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Ok, thanks. I didn't realise it was wasted spark ignition, actually didn't not know about such things, but have read about them, and makes sense.

I will fit the sprocket with the vertical line pointing up and the horizontal lines horizontal. I'll then fit the camshaft to that with the lobes pointing downwards as recommended by you Nick.

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I was concerned about this as well, so I looked very hard that pictures in the manual. I did it the way it showed, which is what nick said. Have the cam lobes pointing down and the vertical line at the top on the cam sprocket.

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I was concerned about this as well, so I looked very hard that pictures in the manual. I did it the way it showed, which is what nick said. Have the cam lobes pointing down and the vertical line at the top on the cam sprocket.

Thanks. Last night I actually found a bit in the manual that said to have the cam lobes facing downwards. So I did was you did too...

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