Timing belt noise Ewill3 ,Mark DTM and the A team

[frank moran]

As I mentioned in the past I'm new to the Catera, but wrenching for too many years... Question, is there a T belt noise from these engines even with all new parts. I'm chasing a noise and looking at every possibility. The engine had bent valves when I bought it so I have no knowledge of sounds etc. otherwise it runs like a top.

[Marks DTM Calib]

On new belts you can get a slow swishing from the screen printing on the belt as is passes over the idlers and tensioner...it goes after a few thousand miles

Pop the aux belt off and re-run it to see if it quietens down, if it does, pop a listening stick on the aux tensioner and alternator (the two favourites at high mileage or following an engine wash)

[ewill3rd]

I am no Catera expert, I do know a little about them but I rarely do much with the timing belts. That usually goes to our engine shop, or "heavy duty" techs.
I have done many timing belts on other cars including the old DOHC motors we used in the early to mid '90s when I worked for Chevrolet.
Some noise on a new belt is normal and usually will quiet down after a while.

What type of noise is it? I have seen other cars with the tension set to tight on the belt cause even more noise, but if I am not mistaken I think that engine has a more automatic type tensioner than the kind of engines I have seen.

[frank moran]

Originally Posted by ewill3rd

I am no Catera expert, I do know a little about them but I rarely do much with the timing belts. That usually goes to our engine shop, or "heavy duty" techs.
I have done many timing belts on other cars including the old DOHC motors we used in the early to mid '90s when I worked for Chevrolet.
Some noise on a new belt is normal and usually will quiet down after a while.

What type of noise is it? I have seen other cars with the tension set to tight on the belt cause even more noise, but if I am not mistaken I think that engine has a more automatic type tensioner than the kind of engines I have seen.

it is a whirring type of sound almost a very low growl, but all the idlers are new. It does sound like a belt that is to tight, I have about a 1,000 miles on it. The car only has 22K on it, the original idler broke. The belt has a quasi self tensioner, but you do have to tension it with the offset rollers and the tensioner...I'm going to open it up again and take another look.....

[Marks DTM Calib]

I assume the correct locking and timing tools were used for belt replacement and that everything was setup with plugs fitted?

Note....the offset rollers are for degreeing the cams in, not setting the tension.

[frank moran]

Originally Posted by Marks DTM Calib

I assume the correct locking and timing tools were used for belt replacement and that everything was setup with plugs fitted?

Note....the offset rollers are for degreeing the cams in, not setting the tension.

yes, that is correct, I had the GM Kent Moore tools...yes the tensioner is the one with the tab and reference point on it, the middle idler is to reference the 1-2 cams, the one on the lower Right is for the 3-4 cams. In the directions the book says turn the pulley for 3-4 cams to approximatley 12 o'clock or .04 deflection, and 1-2 pully to approximatley 12 o'clcock. To me this is too tight, what has your experience been on belt tension, have you been going to the clock reference points that I mention??? I set it up at 12 and 9, to me it has the sound of a tight belt???

[Marks DTM Calib]

I find that setting the lower right idler to 3 Oclock and he upper centre idler to 12 Oclock is the best start point as tghis gives the shortest belt run, then set the tensioner to 5mm (0.2 of an inch in historic measurements) above the marker (new belt).

Turn the crank clockwise through 720deg and re-lock the crank (stop turning it just before it reaches TDC and fit the crank lock then bring it upto TDC).

Then adjust the lower right idler (turn anticlockwise) whilst monitoring the 3-4 cam positions with the timing gauge until the marks are nicely aligned, repeat the process with the upper centre idler (again turn anticlockwise) whilst monitoring the 1-2 cam positions with the timing gauge.

Reset the tension to 5mm above the mark and turn the crankthrough 720 deg again and re-check the timing and tension, adjust as required....if you do adjust it then repeat the 720deg crank turn and re-check each time until you are happy.

What you generaly find is that the lower right idler ends up at about 12 Oclock and the centre one as about 9 Oclock so it sounds like its about right....what was the tensioner set to ......the line or 5mm high of the line...

remember that its the tensioner that sets the belt tightness....not the idlers.

Think I have done about 50+ of these cambelts/tensioners now!

[frank moran]

Originally Posted by Marks DTM Calib

I find that setting the lower right idler to 3 Oclock and he upper centre idler to 12 Oclock is the best start point as tghis gives the shortest belt run, then set the tensioner to 5mm (0.2 of an inch in historic measurements) above the marker (new belt).

Turn the crank clockwise through 720deg and re-lock the crank (stop turning it just before it reaches TDC and fit the crank lock then bring it upto TDC).

Then adjust the lower right idler (turn anticlockwise) whilst monitoring the 3-4 cam positions with the timing gauge until the marks are nicely aligned, repeat the process with the upper centre idler (again turn anticlockwise) whilst monitoring the 1-2 cam positions with the timing gauge.

Reset the tension to 5mm above the mark and turn the crankthrough 720 deg again and re-check the timing and tension, adjust as required....if you do adjust it then repeat the 720deg crank turn and re-check each time until you are happy.

What you generaly find is that the lower right idler ends up at about 12 Oclock and the centre one as about 9 Oclock so it sounds like its about right....what was the tensioner set to ......the line or 5mm high of the line...

remember that its the tensioner that sets the belt tightness....not the idlers.

Think I have done about 50+ of these cambelts/tensioners now!

the tensioner was set up per the factory manual, if memeory serves me about .150 above the scribe mark for the final adj.. Question, does the tensioner flex during operation similar to a serpentine belt tensioner? I threw the old one out, otherwise I would look at it. For some reason I have in my mind the nosie is coming from the belt and or tensioner. During operation the tensioner may be bouncing ??? and setting up a noise and transmitting it through the engine????.

[Marks DTM Calib]

When winding the engine over by hand then yes, the tensioner does move as the cams load and un-load, considerably less pronounced when the engine is running

[frank moran]

Originally Posted by Marks DTM Calib

When winding the engine over by hand then yes, the tensioner does move as the cams load and un-load, considerably less pronounced when the engine is running

"A team", I think I found the noise or it found me. Saturday for the first time I heard a little rattle at idle backing out of the garage. Long story short, I noticed that the R inner wheel well liner was loose and missing some of the push pin retainers. I moved it around into position with the intent of getting some retainers..., went on my way and shortly heard a bunch of rattle noise, my heart stopped for a moment then the noise was gone. I have to confess I dropped a bolt or possibly a wrench on the air filter side of the engine compartment that I could never locate, maybe that was it???. I looked hard and long for anything loose etc.the noise was never in rotational sync and had a sound similar to the old air pumps in the 80s but only on light load... anyway maybe it's resolved, it runs perfectly and even better w/o the occassional light rattle....i'll keep you posted and thanks for all the input.
edit; there is still a bit of what i would call T belt or idler whir. Shortly i'll open it up again and take a triple peek.