Can someone please explain this (Cambelt with photos)
 

Ive just changed the cambelt and water pump on my 2008 STI Hatchback and everything went smoothly but after putting everything back together and turning the engine by hand at the crank, Im a bit confused...

Fitting the new belt, everything lined up perfect. The belt marks, the notches and the marks on the cams etc.

Crank:
Attachment 31656

Passenger side upper cam:
Attachment 31657

Passenger side, both upper and lower cams lined up:
Attachment 31658

Removed the holding pin from the auto tensioner and turned the engine by hand to check nothing was wrong. I turned the engine over twice and then discovered this...

Passenger side upper cam not lined up: (ignore the belt mark as these go out of sync and will not line up again exactly until many more rotations)
Attachment 31659

Passenger side, both upper and lower cams not lined up:
Attachment 31660

Can someone explain why this happens? I cannot figure out in my head how a circular belt with evenly spaced teeth turning parts of engine round can one minute have everything lined up but after just 2 turns of the crank to make a complete rotation of the cams, they no longer line up :wonder::wonder::wonder:

PS - The car ran fine before the belt change and Im 99% sure this misalignment is fine and nothing is wrong (hopefully) but Im still confused with the lining up so hopefully someone with a more techy head than me can shed some light.

PPS - As you can see from the pic, I bought a Gates Timing Belt kit from Import Car Parts (excellent service as always btw, cannot fault them! :thumb:)

Thank you! :)

I'm assuming the hatch is the same as a blob / hawk? Assuming it is, when you put the new belt on initially, did you check the passenger side bottom cam Mark was lined up with the belt Mark? You need a mirror to check its lined up as the mark is out of sight. you should check each cam and make sure the belt line and Mark are lined up. Each cam should line up. Start with the top right cam and line the Mark and the groove up (which you have done) and work round from there.

Yep, I triple checked every marking once the belt was on before removing the tensioner pin. All the marks on the cams and crank lined up spot on with the notches in the cover and the mark under the crank sensor. The double marks on the cams also lined up with eachother. The belt marks are for reference only really but they too lined up 100% in the correct place.

It doesn't look to me like you have turned the top can far enough to line up with its marking on the engine. Try turning the II marks so they line up with each other and see where you're at then.
I found mine wasn't 100% in line after a couple turns though to be honest, but it certainly wasn't a full tooth out so left it and it is fine.

1/2 a tooth out happens when you release the tensioner, without clamping the passenger side cam pulleys, yours is now 1/2 a tooth out and will missfire at around 4250 4500 rpm

Advice
 

Hi

As you have stated & done, if all your cambelt guide lines lined up with pulleys you have fitted the belt correctly. (obviously assuming these belt marks are correctly marked).

Turn the crank sprocket a little further past 12o clock (pulley mark lines up with notch on oil pump) & recheck your pulley marks.

See what it looks like then, can just be discrepancy of decks bank to bank.

How can I be 1/2 a tooth out???

Surely it can only be out by 1 tooth, or 2 or 3 etc...There is no 'half' tooth

The belt has 281 teeth, not 281 and a 1/2

:wonder::wonder::wonder:

Exactly. It's 1 tooth out bad luck start again and put it right, it's an easy mistake to make but a pain to start again and sort it out.

Ok, I appreciate all the replies guys but unfortunately I have to disagree.

I have once again removed the cambelt and started from the beginning. I have checked, checked and re-checked everything when installing the belt and lining everything up. All the belt lines, notches and marks line up perfect. I have even counted the belt teeth between each mark and they also check out perfect.

Rotate the crank twice and the belt ends up in the exact same position that you see in photos 4 and 5 above. I am not 1 tooth or 1/2 a tooth (whatever that means) off.

It seems it is an anomaly and I cannot figure out why this happens. Im sure as heck not going to hand crank the engine 280 odd times to see if it lines up again.

It's fine , you are correct , it won't line up on every rotation , it cant possibly cuz the pulleys are different sizes . If you continued to rotate it a number or times (can't remember how many off the top of my head) it would line up again exactly.

That misalignment after a few rotations on twin Avc's engines is normal, best to check your avc's offset readings when its up & running.

Thank you.

I was 99.999999% sure I had the belt installed right but just could not figure out why this happens.

Why does the alignment change with a AVCS engine?

It changes, as although the pulleys are locked in a non running state, their is movement in them, not like a non avc's engine, & all the tolerances always end up on the l/h side.


Fitted a Hatch belt today & its exactly the same as yours on the l/h pulleys.

If you just turn the crank a very little past 12oclock you will even the alignment out from bank to bank.




All the best

Excellent, thank you all. :)

Timing belt has been changed and as said above, depsite every mark and notch etc lining up 100%, they will fall out of alignment after rotating the engine.

I can confirm everything is good and engine runs fine so no need to worry if you have any concerns like me when doing this job.

Thanks for all the advice everyone! :)