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piston valve pockets 7A

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  • #31
    The collection of parts is growing and in no small part to forum members who have posted up advice and tips or sold parts they no longer need.

    It is time for an update as this evening i have done a dry build to check and set cam timing prior to checking piston to valve clearance, the results are interesting.

    This whole thread started off with my question over piston to valve clearance and the effect a maximum head skim might have on this figure, also; will there be anything to worry about in terms of collisions and how much will it affect the cam timing like some have suggested?

    I got hold of a Tommis Billet cam pulley and this evening fitted it all up and measured from TDC on piston #1 - set using my home made piston dead stop tool and a temporary pointer.

    Process:

    #1 TDC set
    Cam sprocket circle marks pointing at each other and intersected by half by the top edge of head
    Cam pulley notch lined up with the V groove in cam cover

    To achieve all this i had to advance my pulley by just over 4 degrees. (I've read each mark is 2 degrees but that wasn't specific to Tommis pulley but you can see for yourself in the pic what it is)

    It seems that a max head skim can have quite an effect on timing. I'm sure it would have run and probably very well but there is something satisfying knowing that now it is set EXACTLY as the factory intended.

    Well happy and the next part is the crucial bit - seeing how much a plasticine snake lying on top of my piston gets squashed after a couple of rotations...

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    • #32
      The up turn in weather has made my unheated garage a more bearable place to be and this afternoon I have been checking the all importance clearances...

      Many thanks to Error404 for his help in this - top bloke with skills to match.

      The plasticine snake went on top of piston 1.

      I built up the head with 1 inlet and 1 exhaust tappet made 'solid' with parts supplied by Alex, tweaked the head down a little bit but not torqued properly so will need to subtract a small amount from any figures.

      Cams fitted and caps tightened, engine timed up.

      I confirmed that the 'solid' tappets gave no lift when the heel of the cam was on them and they didn't so i knew that the valves were being pushed as they should by the cam and not by any mistakes in my measurements for the tappet blanks.

      2 crank revolutions to make sure both cams had done a complete turn and then lift the head off.

      Interesting results!

      Snake compressed into valve pocket left a lovely witness mark that measured to be 3.4mm (as best as you can measure plasticine with a dial gauge)

      I did a second test with my adjustable pulley turned back to zero advance just to see what difference that made and I got pretty much the same result in the valve pocket but, this time I paid attention to the bit of snake near the edge of the cylinder and i found the piston gets rather close to the head. I had been focusing on the valve pockets and not the other bit.

      The piston / head gap is less than 2mm so i'm planning on a skim off the top of the piston to sort that out, strange how the pockets are well clear - where did the original marks on the valves come from?!?

      oh well, a skim and then on to the balancing step!

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      • #33
        As per my PM mate, ~2mm piston crown to head clearance is fine, 1.2mm I run on my build, so I think there’s no need to skim the pistons
        Think you can crack on now and get it built
        Panthero Coupé quattro 20vt
        Indigo ABY coupé
        Imola B6 S4 Avant

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        • #34


          Nice one! I need to deduct whatever it was for gasket crush but based on another member measuring his old head gasket v my new one, that figure was only 0.04mm so not enough to worry my pistons if you are running 1.2mm!

          Thanks Alex, I'll make the call to the balancing people...

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          • #35
            Nice build Steve...I am interested of buy one 7A head on my project. steve briance Can u tell me, how u measure head?If its in tolerance and have to same "meat" to skimm? Are those areas on your 4 reply?Thanks lot mate
            Attached Files
            Audi Coupe Quattro 2.3 20V

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            • #36
              I can't find the link at the moment as using phone to post and document is on home computer. I'll add it at some point as it has pictures which help but the process is very simple.

              Use your dial gauge or vernier to measure through one of the cylinder head bolt holes. The face where the bolt sits to the face that sits on the block is the one you are looking for. A flat steel ruler across the gasket face of the head gives you a clear stop for the end of the gauge you are pushing through.

              My bottom end is still away being balanced at the moment so not built it up yet. I can't wait to get it back, it should be supremely smooth when done. I had a call from the place who told me they found a 7gram difference between piston/con rod weights. 7 grams from the factory!!

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              • #37
                Yeah they are pretty wide tolerances. Steve will go to 0.1g
                Panthero Coupé quattro 20vt
                Indigo ABY coupé
                Imola B6 S4 Avant

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                • #38
                  steve briance Its problem to measure by myself, because its 500km far. And he dont have vernier and flat steel ruler...So i am not sure, if its good to buy a 7A head without cams and cam cover for around 400 USD
                  Audi Coupe Quattro 2.3 20V

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                  • #39
                    I understand it is a big decision to make without seeing what you are spending the money on but when thinking about the cylinder head face that may need skimming - the photo you have posted tells me that there is sufficient material there to be able to skim if you need to. Mine had been done several times and a lot of the surface features on the head in your picture had been machined away. You still have them.

                    Whether it is worth buying without cams for 400 USD, you need to decide that as cams seem to be selling for around 200USD and cam cover 60USD? Seems a bit expensive to me when you add it all up

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                    • #40
                      I collected the engine from being balanced today.

                      Piston / con rod assembly was balanced end to end then weight matched across the set. 7 grams difference as previously said. They had to remove 26grams from the crankshaft damper and 13 gram from the flywheel which needed to be taken off EXACTLY where the redundant timing pins are. Knocking them off saves 6 grams just in case you ever wondered. The clutch also had some work to get it all spot on.

                      For those of you who thought like me 'the clutch looks pretty symmetrical all the way round, how can it not be balanced?' have a look at the pics. There is a pic of standard holes on the circumference and enlarged holes.

                      Taking crank out tomorrow and the block is getting a good blast with degreaser through the oil channels, followed by compressed air until I can be happy there is no swarf / rust / crud left in there that could cause trouble. The balancing place clean as they go but the block has only been in the parts washer after its rebore and may not be clean inside...

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