Camshaft Timing

[Mɐʇʇ]

Have fired the car back up this afternoon and the Bank 2 (Nearside in the UK?) phase position is out of spec on block 093, but in spec on block 090 - but I can't explain why. Obviously I'm missing something - but what?

• New Cambelt, rollers, adjusters and so forth
• Crank Pin fitted for all adjustments
• Cam Bar fitted for all adjustments
• New phasing adjuster fitted
• New Cam Chains fitted
• 15 Chain links verified
• Cam notches verified against cam cap marks.

Measuring Block 090 is OK : -1.5 on both banks with the book calling for -3 => +6

But Measuring Block 093 doesn't look right. Or is this a red herring?

Elsawin only makes reference to measuring block 090 & 094, I can't find any reference to 093 in there at all? (see attached pdf)

Full Cam Phasing Checks.pdf

(272.25 KiB) Downloaded 276 times

What am I missing? Does there need to be some "adaptation" and it's just showing the old values until the motor runs a bit?
Or should 093 be ignored entirely as per elsawin?

[Shoppinit]

93 is the one to go by. The 90 is the value of the dephasing after the ECU takes into account (through adaptation) the difference in timing. This is how I understand it.

So if your timing is off (group 93) by, say, 4 degrees which is still in spec, then after adaptation and if your dephasing system is working ok, when no dephasing is required will read 0 degrees.

I’m not 100% sure on the whole cam timing VCDS thing si I’m open to convincing arguments to the contrary.

I guess I’m trying to say that 90 is only useful for testing the dephasing. Not the absolute timing.

[Mɐʇʇ]

8 degrees - this means, if I bang the crank pin back in, I should see the intake cam notch out of line (retarded/trailing) with the cap by about 1.5mm (assuming about a 25mm shaft dia just there)? I will check it. Enough to eyeball, certainly.

[Shoppinit]

8 degrees is quite a way out. Could you have missed a link on the chain when reassembling?

/there are different chain lengths between the sprockets from bank 1 to 2. It's quite common to miss that there are different numbers of links to count depending on which side.

[Mɐʇʇ]

21 teeth on the gear means 1 tooth would be 17 degrees out I think?

Plus I've already pulled the cover off and recounted, so 100% sure on that front.

I'll pop the crank pin back in and see how the cam marks look.

[Shoppinit]

Yeah, but it’s complicated by the fact that the measurement is wrt crankshaft angle, not camshaft angle.

[Mɐʇʇ]

Ah. Good shout.

Anyway, have already counted the links and they are good, but will recheck everything and post findings.

[Mɐʇʇ]

@Shopp - is a negative reading is "retarded" cams? So in the search for zero on bank 1 (while I'm back in there), if I rotate the cam clockwise (normal crank rotation) to advance the cam within the tolerance of the alignment bar, that might get that one down to 0?

[Shoppinit]

Don't know I’m afraid. I would guess that a negative number would mean the cam was in advance of the crank, but I say that with very little conviction.

[Mɐʇʇ]

Hmm. Annoyingly I would have assumed the exact opposite, so I guess we're none the wiser. I would have assumed that -ve is cam tailing the crank reference marks, +ve is leading.
I'll get the crank lock pin in and see what's what.

[simonpoulton]

Out of interest, is the side with the issue the same side you fitted the new phasing adjuster? Or did you sort both sides?

[Mɐʇʇ]

Yes, it is. So certainly one thing to consider is switching that back out.

[simonpoulton]

Is the data from group 93 fed back from the phasing adjuster, e.g. its current position? And is the data from group 90 fed from the cam position sensor? (Sorry for the questions, I find these computery bits quite interesting)

[Mɐʇʇ]

I have been in full Google mode and I can't confirm 100%.

What I think is that 93 is absolute timing, but probably crank degrees not cam. So 4 degrees retarded on the cam, not 8.

And 90 is relative timing that validates the adjuster is adjusting.

I suspect that a lot of cars might be out of spec, FWIW. Plus elsawin (pdf above) only calls out block 90 and 94, which is also confusing.

Anyway, I'll probably end up having to work it all out the hard/long way, but I'll post anything I learn here.

[Shoppinit]

Elsawin mentions group 93 in the testing of the cam position sensors.