I bought my 04 X350 about 14 months ago. It has the normally aspirated 4.2L V8. This winter, after having the car for 10 or 11 months, I noticed that when the engine was cold, and the outside temp was below 45F or so, the timing belt made a flap, flap, flap noise for the first minute or two after starting, and then settled down. I noticed that the tensioner was getting yanked back and forth while this was happening, and then settled down.
Since the car had close to 80K on it, I decided the first step would be to put a new belt on.....no difference.
My second move was to put on a Gates 38279 tensioner. I did this about a month ago. This seemed to help briefly, but slowly, a flapping sound returned, but again seemed to settle down as the engine warmed up.
Tonight, when I started the car at the office, there was a god aweful thumping noise that did not go away until I had completed most of my 18 mile journey home. Shining a light on the belt in the garage, I can see the forward edge of the belt is shredded, although it is otherwise intact.
I should mention that I turned all the pulleys, except the crankshaft pulley both times while I previously had the belt off. No noticeable issues with loose or noisy bearings, pulleys out of alignment, or wobbling.
So what is going on? Since I need to replace the belt anyway I might just put on a new idler pulley as well. I'm not one to randomly replace components, but at least it is relatively cheap. Does anyone have an insight into what might be causing this?

Thanks
Paul.

 

Hmmm....what is that belt driving? The problem might lie there and the belt flapping is a warning of a problem with it.

 

This is the accessory belt on the front of the engine. It drives (working from memory), the AC compressor, water pump, power steering pump, and alternator. There is an idler pulley that bolts directly to the engine as well as the belt tensioner pulley. Including the crankshaft pulley, I believe the total is 7 pulleys.
I have now ordered a new idler pulley and belt, and hope to receive them before the weekend. This time I will be really giving each pulley a close examination and checking alignment, as best I can given the 2-3in gap between the engine & radiator housing.

regards
Paul.

 

Oneof those accessories may be on the way out. Check each one, but as it happens at a low temperature, it is probably not the air con compressor, as this will not be demanded at a low temp. However it would be wise to check everything. Other thing is that if tensioner is not tensioning the belt properly, this "flapping" will occur due to the varying loads on the belt

 

Hi Fraser,
Yes. I'll be taking your advice and paying close attention to all the pulleys. I am somewhat wondering about the crankshaft pulley. Do you happen to know if it doubles as a harmonic balancer as some other engines use? If so, is it possible for it to be worn or failing and cause the sort of issue that I am having? I have no particular reason to suspect that it might be the culprit, except that it is the only one I cannot turn by hand with the belt off. I suppose I could try to grab it with both hands and see if it can be moved (rocked) relative to the crankshaft.

I'm hoping the new idler pulley and belt arrived today. Will report back on my findings.

Regards
Paul.

 

Hi Paul

I don't think a V8 needs a harmonic balancer, its only a straight six, (or 12) needs it because of the length of the crankshaft. V8 has a very short crank compared to a straight 6. However I see harmonic balancers for the X-type are on the internet, and that is a V6 with an even shorter crank !

Puzzling !

 

Hi Fraser,
Hopefully, I fixed the problem today. I did what I should have done before and removed all the inlet plumbing up to the engine. This gave me a pretty good view of all the pulleys, and made unloading the tensioner much easier. Previously I had just worked from underneath. The old belt had lost a chunk of it's leading edge, and there was a long strip sitting on the plastic shield under the engine. The new pulley rolled more smoothly in my hands than the old one, although I am not sure I can blame the old one for the issue. The new pulley also has a flange on both sides to contain the belt, which the old one does not. Anyway after tugging on all the pulleys and checking for unwanted motion, making sure that none of them had any rough edges, and that they all line up with other, I reassembled. I ran the engine before putting all the plastic intake stuff back on, and it looked and sounded good. The engine seemed smoother on the test drive. I am now wondering if I did not initially install the old belt properly, and maybe nicked it as I forced it over the pulleys as I worked from underneath. I'm going on a 300 mile trip tomorrow. Should be a good test!

Regards
Paul.

 

Good luck and happy journey !

There ain't a lot of room in the engine compartment, is there !