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Vintage XR timing sprocket question.

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Hi folks,

I am working on an old XR-75, specifically a 1974. During a previous round of work I realized that the timing chain and upper gear were showing some obvious wear. When I ordered new parts I ordered all three components, chain, cam sprocket and crank sprocket.

Today I received my parts and was surprised to see that there is no key-way or any other means to secure/time the sprocket to the crankshaft. I can only assume that this part must be pressed off and on. Is this correct? Even more puzzling to me is how to properly orient/time the sprocket to the crank?:applause:

I noticed before that when I timed the engine I had a hard time getting the cam sprocket to align the way I thought it should. It seemed to be either 1/2 a tooth retarded or 1/2 a tooth advanced. :applause: Is it possible that the lower gear was slightly mis-located (or slipped) all along?

If anyone can shed any light on this for me I would be grateful, thanks.

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All I know is that the crank sprocket is pressed. I have never had one in worn condition so never messed with it. Sorry I can't help more. But having the timing off a half tooth is fine. I just don't remember if it runs better advanced or retarded.

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Qwoke-q,

All I know is that the crank sprocket is pressed.
Thanks for for the confirmation.
But having the timing off a half tooth is fine.
So I take it that the teeth are fine enough that you can always get the timing "close enough" This seems rather unusual to me, having worked on autos in the past where both gears are keyed.

Can anyone else add anything here?

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You can't possibly make the timing more than a half tooth off by the placement of the crank sprocket. If it's 3/4 to far advanced, then move it back a tooth and it's only 1/4 retarded. I'm sure someone will argue my point.

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not argueing , i think i'm agreeing with ya qwoke.. but the point of a half tooth advanced or retarded... all the honda horizontal motors i've worked on always line up just a hair off, setting it to the retarded side runs better, but i don't have any prior working exp. opn the 75 motor ( it is a vertical motor isn't it?) i did some re-ring jobs on an xr80 and an XL100 when i was a teenager but that was ages ago LOL

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Turboglenn,

Yes it's a vertical engine, nearly identical to the 80 & 100 you worked on, especially if they were older. Realizing that I was probably in the wrong forum, I posted today in the 80-200 cc forum. Hopefully someone there has some ideas for me. Thanks to both of you for posting.

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