AKL engine strange issue setting timing and affecting pretty much everything else

[k984265]

Hi everyone, I hope somebody here will be able to give me some pointers as I am loosing my hair with this one.

I have a 1998 Golf 4 with the 1.6sr 8v engine (the infamous AKL). Since I bought it about 5 years ago I have steadily been working on the car diagnosing and replacing several things. The car is now about 320.000km. Other than slight misfires at idle, the car was running pretty well. A couple of weeks ago I decided to do the timing chain on it and since then it has been a downhill ride. When doing the timing I replaced a few other bits, such as water-pump, coolant and thermostat and the alternator belt. The timing chain itself was replaced together with the tensioner and I must say that when I checked the timing marks it did not exactly align. I also wanted to replace the crankshaft front-seal as a precaution, since I was going to be doing the timing I figured it was worth doing. Once I pulled the crankshaft sprocket I found that the index on the inside had been sheared and the actual sprocket had rotated some 20° or so, but it was pretty solidly held in place with the bolt. I thought at this point I had found the problem with the slightly irregular idle and slight lack of "power". I promptly changed it with a new unit (the index had not been damaged on the actual crankshaft) and fitted all the new bits. I immediately started getting puzzled because I could not getting the timing marks to align exactly. It always seems that I am about 1/2 tooth out on the top camshaft sprocket (either advanced or retarded). If I retard it the car runs "lazy" - for lack of a better word - and consumption is poor. No error codes are logged. If I advance it, car seems to run immediately better, consumption improves but I get the camshaft implausible error and of course I start getting misfires after 4000rpm and it is virtually impossible to push the engine above 5200 - 5400rpm. Retard it again and it goes back to being lazy. This laziness was present before when I got the car and was solved when I replaced the camshaft position sensor. I even thought (cos a tiny bit of the plastic on the sensor was broken) that I had damaged the sensor when I replaced the timing chain and have changed it again but to no avail. I have checked and changed the timing some 10 times so far and always end up with the same issues.
On a side-note, the crankshaft position sensor is also very recent and I am sure it is working well, so the implausibility code which the ECU throws out when it compares the camshaft and crankshaft position sensors signals seems "plausible". The problem is that no matter what I do, I cannot get the timing marks to align correctly... I have though that the head has been skimmed, but cannot imagine such an amount of skimming that would make such a difference (1/2 tooth). Having said that when I did a compression test (very recently), I have found all cylinders reading above 14 bar which does sound quite high for this engine (and the variation between cylinders was no more than 0.2bar and all were getting there pretty much in the same short amount of time).
Has anyone ever had/heard of such a problem before? Could I truly be looking at an over-skimmed cylinder head?

P.S.- I have also checked the teeth "design" of the water pump and on the new timing belt and all seems to match up with the existing gears...

[k984265]

Any thoughts anyone?

[micheal balbrig]

As I am not Familiar with your engine type, all I can suggest is to see if your crankshaft marks are in line when number one piston is at actual tdc

[k984265]

Thanks for your thoughts. I have checked this at the very beginning and everything seems to check out on the "bottom-end" with both the distribution and gearbox ends TDC marks aligning and matching with n°1 reaching the top (checked through the spark plug hole)...

[micheal balbrig]

Only other thought would be if the cam / sprocket,were same set up as tdi.
The cam and sprocket are a taper fit on tdi (no keyway),and can rotate on spindle to ensure precise timing.

[k984265]

Sorry for the late reply. Got caught up with other issues.
Unfortunately it is not so "easy" , as this engine is keyed, both in the bottom sprocket as well as on the top one. As far as I can see, the only variable, other than the normal tensioner adjustment is the diameter of the water pump sprocket which is the only other thing that is driven by the timing belt...

[micheal balbrig]

Well by being keyed eliminates that thought.
Not sure what was wrong with crank sprocket,but I expect you double checked here for solution.

[Col]

It is a trial and error thing.

Incidentally I thought they were belt driven, not chain. I've done a 1998 1.6 SR 8v and it was most certainly a belt. And also vaguely remember them having a tapered sprocket that runs free on the end of the cam once the taper is broken (could be wrong there as it was a few years ago).

Regardless of that, the trouble you are probably having is when you apply tension to the chain / belt, it pulls the timing out by half a tooth or whatever you are getting. The solution is to knock the cam back half tooth (or link in your case) so when you apply tension it pulls it back into the correct alignment. Takes a bit of trial and error to get right.

[k984265]

Well by being keyed eliminates that thought.
Not sure what was wrong with crank sprocket,but I expect you double checked here for solution.

I have sort of left it as it was, as I thought a few nights sleep over it might bring some bright ideas, but nothing. The problem with the crank sprocket was that the inside key had sheared and the sprocket had rotated on the crank 5 to 10°... I know that the car had a blown engine when the timing belt snapped on a rolling-road test some years back (driver got it in the wrong gear...) and I know that the whole top of the engine was rebuilt. I assume that they never removed the crank sprocket and refitted everything back. Since the timing was ok, there was no other reason to be suspicious...

[k984265]

It is a trial and error thing.

Incidentally I thought they were belt driven, not chain. I've done a 1998 1.6 SR 8v and it was most certainly a belt. And also vaguely remember them having a tapered sprocket that runs free on the end of the cam once the taper is broken (could be wrong there as it was a few years ago).

Regardless of that, the trouble you are probably having is when you apply tension to the chain / belt, it pulls the timing out by half a tooth or whatever you are getting. The solution is to knock the cam back half tooth (or link in your case) so when you apply tension it pulls it back into the correct alignment. Takes a bit of trial and error to get right.

Thanks for your input. You are right that it is a belt, but there is no taper. In fact, both crank and cam sprockets are keyed! No adjustment possible on that as far as I can see. The only variable is really the length the belt runs.
I understand what you say about the tensioner messing the timing and for that reason I have tried advancing and retarding the timing by one tooth, but on doing so I immediately get problems with the cam position sensor signal becoming implausible as it runs too far of the mark on the flywheel (with the rough running and not pulling over 5200rpm).
There is the issue with the compression ratio as well which I measured across all cylinders at 14bar above atmospheric on cranking with variations of no more than 0.2bar across all 4 cylinders... Doesn't this seem too high? I know it does seem so to me... My only "theory" for all this is that the head has been skimmed so much on the previous repair that I got such a rise and hence the difference also on the timing as the length from crank to cam sprocket was reduced. Sounds plausible?