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Thanks all for your input and comments. I've checked with the machinist who worked on the heads and he verified that he would have checked the springs. Although I would have sent him the springs and valve parts in zip-lock bags (one for each cylinder), he indicate that he would not have kept them separate, so it is unlikely that springs/valves initial on the failed cylinder #5 would have landed back on that cylinder. I do not want to mention the machinist's name here as he is a very well respected machinist in the Porsche community and I don't intimate that this problem may have been caused by him in any way. If he said he checked the springs, I believe him. That said, I'm not sure why the valves from just one cylinder would depress that much easier than the others.
While valve noise is typically a ticking, I think that is usually due to the contact made b/w the rocker and valve when the gap is not set appropriately. Knocking usually means connecting rod/piston sort of issues, but as Fast Corners says a floating valve due to a weak/broken spring might make contact with the piston head and sound more like a knock.
I didn't realize that there was a tool to remove the valve spring w/o removing the head. I will likely pull the engine out of the car anyway as its easier to work on. The hour I spend pulling it out/putting it back in will be worth it so I can see things easier.
Does anyone else have any input on how hard it is to push down a valve? As I say, with a bit of thumb pressure on the rocker arm, I can lift all the valves off their seats - #5 valves just seem to be easier to lift and I can push them a bit further.
Thanks again.
Geoff
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