A couple questions about the timing system on the 1.9T S40 (2000). Tech maybe you can explain it a little bit?

I want to know if (when replacing the timing belt) the camshaft (with variable valve timing) slips, can one simply rotate the cam back into proper alignment? If not, why not? I would think that the variable valve timing would just reset itself when the engine is restarted, provided the alignment marks are correct. I have asked some Volvo techs and some other mechanics as well. The Volvo guys, excepting only one, all say that you need to do a realignment with the special tool that affixes to the rear of the camshafts while most other mechanics that I know just say that they rotate them back into position. Now, I just want to understand why it's not possible to rotate the camshaft back into position. I checked the Vadis manual and it really doesn't say anything specific about the camshafts, except to ensure that they are in alignment.

Maybe if someone can provide a brief synopsis of the inner-working of the variable valve timing system.

Thanks

 

You can rotate the cam back to where i lines up with the timeing marks, when i do a timeing belt on a VVT i always put the car in time, check all marks, then go a 1/4 turn further, then go back that 1/4 and put it back in time, that unloads the hub, take old belt off, replace the tensioner and idler, replace the belt.

 

This it the best way I found to do it.
Line up the timing marks. The remove the top cover where you line the marks up to.
The using either paint or whiteout make a mark from the back of the pulley to the Cam cover.
Make sure they stay lined up. If it moves slightly then just make sure the marks line up and you will be fine.

The system works on pressure applied to the inside of the pulley to advance and retard the timing.
It seems alot more complicated than it is to work on them and get them going.

 

Thanks for the responses Tech and VolvoTechKy. I really appreciate it.

I have a couple follow-up questions for you both:

VolvoTechKy: When you say that the hub is unloaded, do you mean that the CVVT pulley won't have a tendency to slip on it's own? Conceptually, I envision that the oil pressure that is used to adjust the timing pushes against a spring; and, when the engine is off and there is no oil pressure, there is nothing to counter-act the spring, so the pulley is more prone to slip. Thus, unloading the hub reduces this propensity for slippage by eliminating the spring force. Is this right? Then, as a consequence, if the camshaft accidentely rotates while the timing belt is off, it's ok to simply rotate a CVVT pulley back into position so long as the timing marks are in alignment as the pulley will reset itself. I'm just trying to understand the details.

Tech: When you say to mark the back of the pulley and the cam cover, do you mean ensure that the actual camshaft, itself, is still in proper alignment?

Thanks for you responses, it really helps me out.

 

Yes this way you know it is lined up from where you took the belt off.