[tamathumper]

It depends on how many times it has been re-printed, "fit to margins", etc. A direct photocopy set at 1:1 is maybe reliable enough, but one that's bounced around a few times, especially as a PDF, is entirely suspect. If I'm going to machine something I want to get it right the first time.

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[Cloud9...68]

Hmmm... So if this tool is all that's needed to set the cam timing, why mess with the silly dial gauges, running compressed air through the leaky variocam, etc.?

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[tamathumper]

Could just be a rough-set tool for placing new cams, I can't seem to find any description of it beyond the workshop manual's very rough translation.



But, in woodworking we always trust a direct relationship of two objects over a measured relationship, and that's the basis of any "jig" or "fixture", so I'm wondering if this isn't the tool I think it is, can one be made that has those exact profiles on it and would make timing that much easier?

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[Bulti]

[quote name='tamathumper' timestamp='1376074489' post='146922']You can measure vacuum with an inexpensive vacuum gauge - your friend with the Bosch Hammer should definitely be able to help you there.



Faxes are notoriously "fit to margin" and usually very low resolution, so no I can't trust them, and unfortunately Porsche dealers don't want to share anything, not even the distance between two straight lines.[/quote]



As what the sharing is concerned, you are absolutely right, they wouldn't even lend me their flywheel lock... Like they still have 968's comming in every day for a belt job...



Btw, I just found out my bottom balance shaft sprocket was 180° out of allignment (the sprocket was mounted the right way on the shaft, but didn't line up with the pastic notch on the rear belt cover). I guess that wouldn't help things either :-)

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[Bulti]

[quote name='Cloud9...68' timestamp='1376071985' post='146911']Have you done a blink test yet? If not, this should be the first item on your list. It doesn't provide any quantitative information, but will tell you if you have a bad sensor of some kind. Best of all, it's free.[/quote]



Do you mean the test with the "Check Engine" light? Does this even work on "ROW" cars?

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[Cloud9...68]

[quote name='Bulti' timestamp='1376077309' post='146935']

Do you mean the test with the "Check Engine" light? Does this even work on "ROW" cars?

[/quote]

Yes, that's the test I'm referring to. I thought it worked on ROW cars, but to tell you the truth, I'm not sure.

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[tamathumper]

The procedure I have for the Blink Test specifically says "Not for ROW cars", but doesn't say why.

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[Rob in Oz]

[quote name='Cloud9...68' timestamp='1376075380' post='146927']

Hmmm... So if this tool is all that's needed to set the cam timing, why mess with the silly dial gauges, running compressed air through the leaky variocam, etc.?

[/quote]



It's a confirmation that you haven't got the cams out of sync by a tooth either way. Apart from the VarioCam mechanism, there's no way to alter the relationship between the two cams, as they are hard-linked by the cam chain. All of your adjustments will only alter the relationship of the exhaust cam (and, because of the chain linkage, the inlet cam) with the crankshaft. The faffing around with dial gauges allows the timing to be optimised for the inlet cam, with the timing of the exhaust cam being (so I'm led to believe) less critical and so altered to allow the inlet to be spot-on.



Rob

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[Bulti]

You should think that a lightbulb couldn't possibly know on which side of the ocean it's at :-)

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[tamathumper]

I do see some posts online that indicate it's a rough-in tool, but I can see how it (or one much like it) could be used as a spot-on tool as well. The cams are in lockstep, and once you know their inner faces are vertical at <acronym title='top dead center'>TDC</acronym> for cylinder 1 there's not much chance of being off by an entire tooth.



But more to the point, at <acronym title='top dead center'>TDC</acronym> they have to be oriented in an exact position, and there's no reason (I am aware of) that that position could not be indicated with a jig?



Or, I could be completely wrong. Again.

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[Cloud9...68]

Is the reason the variocam needs to be activated during the cam timing procedure simply because without it, the chain would be loose, and therefore not able to accurately set the physical relationship between the two cams?

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[tamathumper]

To put it most simply, it needs to be activated so that the relationship between the two cams is "known", and not a variable.

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[flash]

because the valve may or may not extend a particular amount, you have to use dial indicators to determine where the valves are in their cycle. it's all about degree of overlap. a fixed too would only work if the valve were opening a known amount. they get close with pressure applied, but depending on wear and leakage, cannot really set it. hence, the adjustment. if there were a tool that would extend the valve to a fixed distance, factoring in chain and cam wear, then a fixed cam tool would work. a lot of variables to try to work in though.

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[tamathumper]

Bummer. How can the valve extension vary independent of camshaft position? The cam and chain wear aren't really taken into account by the procedure as far as I can tell?

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[flash]

the valve extension varies based on the wear of the valve.



cam and chain wear are taken into consideration as the adjustment is made. you move the cam a different amount based on how worn it and the chain are. it's not like there is a calculation or anything, but you would move the cam more with worn parts than with new ones. basically you have to take up more slack with worn parts. that changes the cam positions relative to each other. consequently you have to alter the adjustment to put the valves back where they are supposed to be

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[tamathumper]

Poop.

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[flash]

lol - yeah - pretty much how i felt too

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[Cloud9...68]

Flash,



That's a very nice explanation which clears up a lot of questions I had about the procedure - thanks.



But a big remaining source of error is the variance in the amount of wear in the variocam piston seal itself, which causes the degree to which the chain is extended to vary. So it does sound like your builder's method of using oil to pressurize the variocam is the closest thing to the perfect method that exists.

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[flash]

that would be my conclusion as well.

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[Bulti]

Guys, I'm happy to announce my horses are back in the stable!

The bad engine performance was due to a nearly completely desintegrated connector of the speed sensor at the flywheel (next to the hole where you check the <acronym title='top dead center'>TDC</acronym>). The sensor itself was also dented a little bit! Maybe I damaged it when replacing my flywheel some time a go?



Also cleaned the <acronym title='mass air flow'>MAF</acronym> and every sensor I could find in the area just to be sure. The only issue I got left is some pretty strong vibrations when I shift back and use the enginebreak from higher rpm's (about 4500). I suspect my balance shaft belt is the cause. Could it still be too firm, or too loose? I can twist it about 135° between my fingers, right at the waterpump pulley.

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