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The Garage Motorcycle Related Discussion (Yamaha XS650, other makes and models, and anything else motorcycle related including tools and gear)

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Old 04-07-2013, 09:08 PM   #1
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Default valve adjustment

Is there another way to determine tdc besides lining up the mark on the rotor? The reason I ask is because the rotor on this 80 special I am working on is new and there doesn't seem to be a clear mark. I adjusted the valves using what I believed to be the mark, but it is difficult to see, and is a very small, but seems to be a clear endent on the edge of the rotor. The reason I am not completely sure about the mark is because there seems to be slightly more noise from the valves, like the gap is off, when the engine is running. Thanks
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Old 04-07-2013, 10:38 PM   #2
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Default Re: valve adjustment

Pull a plug and look. Youll be able to see when its there. That will be close.enough for doing the valves

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Old 04-08-2013, 06:55 AM   #3
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Default Re: valve adjustment

Common practice is to:

1 - Remove spark plug
2 - Rotate engine counter clockwise as viewed from the left side
3 - Watch for intake valve to open and close
4 - With long screwdriver in the spark plug hole feel for when the piston next reaches it's highest point
5 - Check both intake and exhaust valves, both should be loose, if not go to step 2
6 - You are now close enough to TDC on the compression stroke to allow adjustment of the valves
7 - Adjust valves
8 - Go to step 1 and repeat for right cylinder
9 - Replace plugs, start bike and adjust cam chain
10 - Your done!!!

Last edited by Brian902; 04-08-2013 at 08:34 AM.

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Old 04-08-2013, 07:18 AM   #4
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Default Re: valve adjustment

+1, if the rocker arm is on the base circle part of the cam profile, it is close enough for valve clearance setting. Basically the valves on the other cylinder will be in the overlap/open area. The engine will tend to want to turn to and sit in the "valley" between the valve ramps on the other side that's plenty good for valve setting.

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Old 04-08-2013, 08:27 AM   #5
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Default Re: valve adjustment

If you really want to get accurate, Hugh's Handbuilt had a really nice Blog post on this.
tdc and how to find it

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Old 04-08-2013, 08:02 PM   #6
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Default Re: valve adjustment

Thanks everyone for your input. I should be able to handle it from here.
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