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  • Cam timing

    Ok it's been a while. Getting back to building the engine for the urq and I'm struggling to remember how to do the cam timing. What I mean is the chain between the 2 cams. So am I half a link or 1 tooth out? How many links should be between the 2 cams vertical position?

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  • #2
    Here is a picture I found on the net, seems 1 tooth closer than mine.

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    • #3
      And this seems to be half a long shorter.

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      • #4
        Basically its this thread I'm looking for but the pictures have gone.

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        • #5
          No one? 9 links, 10 or 11 between the vertical points on inlet and exhaust cam?

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          • #6
            Line up the two marks on the cams so they point at each other, you cant get it wrong.
            91CQ20v - Gone to a new home
            93UR-S4 - The Magic Carpet
            94S2Bus - The Emerald Express

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            • #7
              All of these photos are confused by looking down on them at an angle but if you have the dots: look at them directly from the number 5 end of the head - it's tight to get an unobstructed view but look along the tops of the spark plug holes and see if the CENTRE of the dots are level with the machined top edge of head where gasket sits. That is right on 7A and 3B at least and uses manufacturers marks.

              Is your chain very old and worn? Excess slack might have something to do with it but probably not as much as half a link.
              Last edited by steve briance; 22nd October 2019, 21:09.

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              • #8
                Mine (3B) is easy to line up. They '0' marks line up nicely. If you're one tooth out they are nowhere near each other.
                91 Modded 3B
                14 A6 Avant Black Edition

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                • #9
                  Thanks guys. Chain is fresh and nice and tight. At 9 links between them, the cam marks are below the surface of the head slightly, at 10 links, they seem closest to flat level, and at 11 links they sit above the head surface slightly.

                  This seems a fairly common issue as can be seen from the pics I found with all 3 options in place. I wish that motorgeek thread still had the pictures as it showed examples counting the links as to what was wrong and what was right.

                  It's made more confusing with a Vernier cam pulley and a custom flywheel with no tdc marks. Ideally I would like to measure cam lift and set it up that way but I can't find figures for that.

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                  • #10

                    You got me thinking now, here is mine I did a few weeks ago, couldn't get over the difference in chain tension.
                    Second picture not timed up but showing old slack chain.
                    New one is like guitar string.

                    cam timing.jpgtiming.jpgdroop.jpg

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                    • #11
                      Yea it's an interesting 1. My chain too is quite tight. So, count from the 0 mark on the cam up to find vertical. 7 teeth Inc the zero tooth? Mark that point on your sprockets. Now count the links between the 2 new vertical marks. 9, 10 or 11.... I can't quite see the vertical position on yours.

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                      • #12
                        Measuring valve lift is difficult if you have hydraulic tappets... You have to make or buy a solid lifter to remove the way in which the hydraulic version takes up clearance. It won't take up clearance when not running as there is no oil pressure and turning the engine over by hand will probably squeeze out a small amount of oil that is left in there and then you are just guessing what your clearances /lift figures are! ​​​​​​

                        There are such things as adjustable cam sprockets to fit onto the end of the camshaft but unless you have wildly different cam grinds, I'm not sure you would need that. They adjust in the same way as vernier pulley, how you get them on the end of the shaft I've no idea! Maybe heat?...

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                        • #13
                          Originally posted by steve briance View Post
                          Measuring valve lift is difficult if you have hydraulic tappets... You have to make or buy a solid lifter to remove the way in which the hydraulic version takes up clearance. It won't take up clearance when not running as there is no oil pressure and turning the engine over by hand will probably squeeze out a small amount of oil that is left in there and then you are just guessing what your clearances /lift figures are! ​​​​​​

                          There are such things as adjustable cam sprockets to fit onto the end of the camshaft but unless you have wildly different cam grinds, I'm not sure you would need that. They adjust in the same way as vernier pulley, how you get them on the end of the shaft I've no idea! Maybe heat?...
                          You can measure how much the tappet is depressed to determine lift. Need to make up a suitable jig to mount the dpi gauge but easy enough. But I can't find figures for 7a cams at tdc. Yea I think you use heat to swap the cam gears, which I haven't done. Just looking to set up 7a cams as per the book.

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                          • #14
                            Originally posted by diesel des View Post
                            Yea it's an interesting 1. My chain too is quite tight. So, count from the 0 mark on the cam up to find vertical. 7 teeth Inc the zero tooth? Mark that point on your sprockets. Now count the links between the 2 new vertical marks. 9, 10 or 11.... I can't quite see the vertical position on yours.

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                            Used my phone low down to take picture.
                            Looks like a 9 to me cant get another look as away from home at the moment.

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                            • #15
                              I'm at 10... Seen others at 11. Why is this not simple.

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