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Discussion Starter #1
72 daytona when i am at tdc i have dots lined up on my cam spockets and not the lines. I bought this bike as a basket case and someone else has the bottom end assembled. What does not seem right is the manual says the lines should be lined up instead of the dots. I don't know what the dots are for and when the dots are lined up at tdc i have both valves on the same cyclinder open. Should i just turn one cam until i have 1 exhaust and opposite intake valve is open? Sorry if this sounds confusing but you never can trust anyone elses work.
 

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Discussion Starter #2 (Edited)
I figured out the dots are for a single carb but both valves on the same cylinder open at the same time can't be right. Maybe the sprockets were put on the keyway the wrong way. The manual says to mark the sprocket when you take it of the cam but there has to be a way to start from scratch.
 

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When one cylinder has both valves open, both valves on the other cylinder should be closed. When the piston nears the top of the exhaust stroke the exhaust valve starts to close but doesn't close completely until the piston has passed top center. The intake starts to open just before top center so at top center, where all the dots and lines on the cam wheels are lined up, there is a bit of overlap when both valves will be a bit open. When the piston reaches top center on the exhaust stroke it quits pushing exhaust gas out the port. Because there is suddenly nothing pushing the gas, the pressure of the exhaust turns slightly negative at the port. When the intake starts to open this negative pressure helps get the intake flow going because the exhaust gas has already been accelerated through the exhaust pipes and the outward flow of the exhaust helps pull the fresh intake charge into the port kinda of like a siphon. The exhaust valve closes just after top center and the downward movement of the piston pulls the rest of the intake charge into the cylinder. I hope this makes sense. It is the way I understand it to work.
 

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Discussion Starter #4
Thanks Jimmy that makes sense. I now wonder what is the difference between single and dual carbs with the cams and should i take the sprockets off to line up the lines instead of the dots or take the center srocket out so i can rotate the cams so the lines line up.
 

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I think the cam indexing is the same for single or dual carbs. The correct timing for your engine will be layed out in a shop manual specific to your engine.
 

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Discussion Starter #6
My haynes manual says nothing on where to place the cams except to mark which keyway the gear is on before taking it off. I never put them on so its a guess. It also says line dots up for single carb and lines for dual carbs so there must be a difference. On overhead cam bikes they usually tell which way the lobes face at tdc. I don't understand what the difference would be from a single carb to a dual carb as far as cam indexing.
 

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The dots on your photo are lined up like the illustration in the manual for a 72 single carb. I can't tell where the key way with a cotter pin is because the cam nuts hide it. The manual is a bit unclear to me. It calls for the keyway to be "directly opposite" the timing mark. To me that means on the opposite side of the wheel from the timing mark but the illustration of the wheels have the keyway in line with the timing mark on the same side as the mark. I have always had a difficult time interpreting English from England. I think "directly opposite" means "next to" in Brit speak. (Any of you Brits have a different opinion, chime in here.) If you put the cam key back in the same slot of the wheel it came out of you should be good.
 

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Discussion Starter #8
Thanks Jimmy for trying to work through this with me. The way it was in the photo was not right because both valves on the same cylinder would have been wide open at tdc.I understand that there could be a slight overlap on valves but wide open would maybe means bent valves and no compression.I took the center gear off and rotated the cams so the lines lined up instead of the dots and now rotating the engine clockwise it looks like the valves are opening and closing porperly. I am just going by watching the tappets and tdc as there is no head on the bike yet. So the last person to work on this bike must have had the sprockets on the right keyway but for some reason lined the dots up instead of the lines. All is good.
 
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