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piston valve pockets 7A

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  • piston valve pockets 7A

    Hello all.

    I am in the process of getting bits together to rebuild a spare 7A head and today when I was cleaning, I noticed the inlet valves have marks on them which may be a bit of a worry.

    Head is second hand so i don;t know how many times it has been skimmed but to me, it looks like it may have been a couple of times and as a result the inlet valves are touching the valve pockets ever so slightly and when i say slightly i mean it has made no impressions into the surface of the valve, it has just polished it. I don't think it could be a result of timing belt snapping as the marks are uniform on all valves and they slide nicely in their guides.

    Is it feasible to have the valve pockets machined out to give me back the clearance? It looks like there is plenty of meat in the top of the piston but that is only guesswork as I've never seen one cut in half.

    thanks in advance for any advice or anything else you may think needs to be done to revive the head.





    Attached Files

  • #2
    If I were You I would measure cylinderhead height.

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    • #3
      Put up picture from head, where can be seen the surface of it.

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      • #4
        I've just been out trying to measure head. difficult as the rocker cover surface is obviously angled from the face that meets the head so where is it measured from?

        Anyway, as luck would have it, i remembered a scrap head knocking about which i know has NOT been skimmed.

        first picture shows that head in its original state.

        second picture shows the replacement head and it seems that the surface features have gone and at least 1.3mm is removed as that is how deep the surface features are on the untouched head and are missing on the new head.

        third picture shows inlet port on scrap head.

        fourth picture shows inlet port on replacement head and why i would like to use it
        Attached Files

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        • #5
          If 1.3mm has been removed, you've probably got 2 scrap heads
          Mike

          http://www.s2-audi.co.uk

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          • #6
            oh.

            Other than the issue of valves getting a bit too close to the pistons, are there any other problems that excess skimming causes?

            If I had the valve pocket machined down by 1.3mm isn't it effectively the same difference as far as valve / piston relationship goes?

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            • #7
              Mike, i have just found the workshop manual you posted on s2-audi.co.uk

              Max workshop figure is 118.1mm measured from head face through head bolt to face where bolt head washer sits.

              Mine is 118.3mm which makes me think i have 0.2mm in hand! This is for an AAN head though which i am aware has different pistons so perhaps i need to find a 7A workshop manual...

              edit. 7A manual says same 118.1mm.
              Last edited by steve briance; 17th December 2017, 18:03.

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              • #8
                Yea, but is that measure only to keep timing in some reasonable spec?(= no problem with adjustable pulley) Or is there some structual issue with the head after that measure?

                I can happily give an address where to send all those scrap heads that are under the 118.1mm spec.

                Audi UrS4 Avant 2.5 20vt - twincharged - Project
                Audi 80q B4 Sedan 2.2 20vt - Daily user
                BMW 320d Touring e91 M-Sport - Daily user
                BMW 740iA e38 - Project

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                • #9
                  Steve, Check the depth of the combustion chambers on both heads...should give you a better indication of the valve lift.

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                  • #10
                    If you need pistons machining drop me a line
                    Panthero Coupé quattro 20vt
                    Indigo ABY coupé
                    Imola B6 S4 Avant

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                    • #11
                      You're right on the edge of the spec there. No more skims for that head. As indicated, you'll likely need to make changes to the pistons for clearance
                      Mike

                      http://www.s2-audi.co.uk

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                      • #12
                        Blue tak on the pistons, fit and lightly torque head bolts with an old gasket in place and then measure blue tak thickness once you remove.

                        Guess you don't have the bottom end to see if the pistons were marked?

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                        • #13
                          Oh, and shine a bright torch through the ports, and in a dark room do you see any light coming through the valve?

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                          • #14
                            Thanks all for your input! much appreciated as it doesn't sound like complete doom and gloom, just a little more effort and that i can live with.

                            Bowie69 - as it happens i do have the bottom end and the pistons show no obvious sign of impact, it must be reaaaally close though I bought the engine complete and on dismantling i had no reason to doubt the guy who said it was a runner though i never heard it. The bearing shells were just worn rather than damaged, pistons have got no scuff marks on the skirt and there is no oily blow by so I think the bore/ring seal was good. Valves have all been lapped in now and petrol leak test shows nothing dribbling through into the ports.

                            Overall I was quite pleased as a previous 7A i'd taken apart was so gummed up that none of the rings moved in their grooves! Pic shows the state of the other engine before and after cleaning, this one i did hear running and it didn't sound too bad either!

                            Attached Files

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                            • #15
                              I dread to think what my 204,000 mile 7A looks like

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