Perhaps 'irregular' would be a better description, and it's too slow to relate directly to engine rpm.

I would expect tensioner/chain issues to manifest as a rattling noise.

 

Hi Marko,

Seems a belt tensioner not providing smooth tension anymore. Or misalignment of the generator pulley.
Try looking down the front of the engine when someone starts your car and you will notice.


Good luck.

 

Thanks for the ideas, I will check that. So if I undersrand correctly the issue can be caused also by failed pulleys on other components (like alternator, A/C condenser, power steering pump or the supercharger)? I changed all “servicable” items about 1000 km ago - the idler pulley, the belt tensioner including mounting bracket and the serpentine belt - both on the supercharger assembly and on the engine drive belt assebly. Water pump was renewed also at the same time. Would some error when installing these items cause such problems (for example wrong torque on the bolts)?

Many thanks for your help!

 

Could be indeed. I personally scr*wed up that a while ago by forcing the tensioner back too far to take the belt off. It slightly off set (bend) the bolt of the Idler. It was almost invisible even when bolt on the bench but caused almost the same thing. Next to that my alternator bracket mounting had been fiddled with by PO, so it took a while until all was well again.

Never to proud to admit a mistake:-) (Even in diagnosing based on a clip...tooo hard, but hope it helps to look for yourselves)

 

Torque figues alone wouldn't cause an issue (unless something is physically loose?), although a pulley misalignment could.

Ekskaar's suggestion was better than mine as you wouldn't have to remove anything to check, so I would try that first before dismantling anything. Did the problem start immediately after the pulley/belt change?

 

Thanks guys! I am not really sure when the simptoms started. I bought the car in june, after it was standing for three years. On first start I remember some strange sounds, I think they were the same, but not 100% sure. At this time there was also loud squeaking of one of the belts, so the shop suggested changing everything. Since that I did not notice this loud knocking until recently. It seems however to be related also to outside temperatures - I did not notice it during summer, now when temepratures are lower it also happens only when the car stands for a couple of days. When I leave it in my garage overnight it does not happen. I do not use the car very often, I only managed 1000 km this season - mainly driving it to different shops to sort out problems (usual things as ceiling, lower steering column knock, some small paint repairs and dents removal,..) as I want it to be perfect

 

Best as I can ascertain the frequency is 1Hz or 60rpm or 1/16th engine idle at start up (960rpm)

Belt length is 2271mm, a complete guess at crank pulley dia is say 220mm, making a circumference of 691mm so belt makes about 290rpm at idle so unlikely belt related and I can't think of anything else rotating at 1/16th of the engine speed so unlikely to be engine rotation related.

My best guess unrelated to engine rotation speed is the AC clutch trying to engage and failing - try turning all of the heating off or pulling the AC clutch fuse.

 

Nice analysis indeed.
Can you include the third dimension and other relevant ingredients as well?
Lateral movement, lateral movement speed, max lateral movement before snapping back in place, temperature impact on lateral directed force (friction) between belt and tension pulley, more...?
(Effect of engine standing still, --> little more tension applied to half the belt loop by rotational resistance of the axles and pulleys in the system. After cold start this is evened out in 1st few engine revolutions...causing tensioner then needs to actuate more then under normal steady operation....)
Sometimes it is easier to just have a look.;-)

 

Yes it is but I can't see from here, and there are many things you can't see from there either.

Basically despite your p**s take, looking at all the things listed in #23 is a waste of time as they are all going to relate to the speed of the pulley concerned.
I'm just trying to provide a clue to assist the OP - the noise is either a)totally unrelated to engine rotation speed, or b) something rotating at 1/16th of the engine speed - so unlikely "failed pulleys, alternator, A/C condenser, power steering pump or the supercharger."
If an idler pulley was the cause as you seem to suggest then that would happen at around 5 x the frequency in the video as it would be once per belt revolution.

 

I am from where they use wooden shoes ;-) so please help me: p**s??
But anyways..Oops, no pun intended, just trying to help by using some experience in lieu of calculated theory... (but not saying your input is not true!! my appologies where needed.)
Let see what comes back from TS.

If you cant wait, see what the distance is between pulleys is where tensioner is putting tension somewhere halfway, and divide by total belt length..
Other option is to see how far the belt off sets during one belt revolution and understand it possibly snaps back into place at 1/16th of engine speed..

 

+1
If the misalignment is small, it may take several revolutions before the belt wanders sufficiently.

 

Sort of sounds like the noise mine made on first startup when it was below 30 degrees F (-1 C). I could see the belt moving back and forth over a rib on the pully. It would realign itself after 3or4 seconds. After a few failed attempts to have the dealer fix the problem, I found an independent garage that specializes in high end cars ( and they still worked on the Jag). Looked like the previous owner had the serpentine belt and tensioner replaced with non- OEM parts (the dealer missed this). He put the correct OEM parts on and it has been quiet ever since. He said something to the effect that in cold weather some aftermarket tensioners took a few seconds to start flexing. Not sure if he was feeding me a line, but, it worked for me.

 

Hello,

Thanks for all the input. I finally managed to take a look at the belts today. It seems that the tensioner pulley makes the noise. I made another video


As already mentioned the tensioner is new. I kept the box and the tensioner is an original Jaguar part.




Is it possible, that the my garage made something wrong during install?

 

Can you see what the belt is doing around the alternator and idler pulleys when this is happening?

Is it running true there or is there some lateral movement?

 

Have to check another day, since the simptoms only come when the car stands for a couple of days. And there is only 1 minute time to check so i have to be quick next time

 

Must be it. Larger diameter getting around pulleys when not in v-shaped tracks.

 

That is what I'm thinking.

@keilwarm79 - good news is it's nothing serious

 

That's good news indeed. My english isn't perfect - what do you mean by larger diameter getting around pulleys? But I will definitely check what's happening on the the other pulleys. Thanks!

 

I managed to make another video today.

You Tube

You guys were right, the belt snaps on the generator pulley. What do you think - is something wrong with the idler puley? Or is it more probable that the generator pulley itself is faulty?

 

I expect the idler pulley is misaligned by its bolt being bend a little caused by the way the Charger belt tensioner was actuated to get that belt on. If not done by using 3/8 square connection but by alternative way it will possibly have applied load on the idler pulley of the accessory belt as wel.

If bolt is straight, then pulley might be wobbly or just slightly lost correct shape.

In past I had a loose generator bracket, is also a possibility here.

good luck