NS petrol, weird whine just above idle when cold

[pneumatic]

Has anyone had issues with gates drive belts? I bought an NS 3.8 petrol, put on new generic idlers and tensioner from onlineautoparts on. Then put on a new gates belt. Was fine in summer. Lately on cold winter mornings the fan belt slips for a few minutes, but is fine when hot. Tension seems strong (I even tried applying extra tension on the tensioner while idling but no difference).

I put on a Dayco w-belt today, made the same noise. Old (not very) gates belt had some contact marks in the roots of the vees at some locations, could the crank pulley be worn out? The rubber on the harmonic balancer is fine, no cracks, no slippage there.



Slip is mostly around idle (just above normal idle, but slightly below cold idle, so cold idle speed once changed into reverse). No change air con on or off, no change with electrical load or steering load.

https://youtu.be/AsnkDDY6yPw

Someone said alternator bearing, surely that would be always noisy?

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[benckj]

Strange one. I’m also interested in the answer as I installed new belts & bearings about 10k ago on my NS and I hear different sounds now. Might be that I’m a little more in tune to the engine after ripping it apart for the first time. Bought all my parts from Rockauto including Gates timing and drive belts.

[Pugsley]

My 01, 3.5 was making the same noise only very loud, found it to be tensioner bearings, I replaced all pullies and tensioner, but after a while, the noise came back. I dismantled it all again and checked the bearings on the tensioner and pullies and found a little play in more than one but bearings seamed to run smooth, so I reassembled it all. What I suspect is the belt causing the pullies to move sideways causing the noise. I try to ignore it now.

[pneumatic]

Today I took the belt off completely and started it, no noise.

Spun the alternator by hand, no noise or play. Bearings should be fine.

Tried putting the old tensioner back on, same noise.

Cut up the old belt to try to make a pulley gauge. Old belt in new idler pulley does not bottom out (pic below). Old belt on old alternator, crank, P/S and A/C pulleys are all closer to bottoming out or bottoming out. Maybe those pulleys are just too worn and need replacing.

Tried sanding the sharp points of the alternator down with an air belt sander while on the car (pic with belt gauge below is after sanding). Was working until the very old sanding belt broke. Started the car, maybe a slight improvement but I may have just exceeded the cold start squeal time for today. Will try again tomorrow.

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[pneumatic]

I think I've solved it. So sanding the alternator pulley peaks down didn't help. I showed the video to a head mechanic while my car was in for a post lift kit wheel alignment. He said fan belt noises are very tricky. On one car they had in the noise only stopped when they put a factory belt on. On another they replaced all the main pulleys including the harmonic balancer and power steering pulley. I wasn't keen on doing that.

I had noticed the back of the belt was looking scuffed (marks shown are after less than 1000km on Dayco belt), and the top idler running on the back of the belt sometimes had rubber on it. I started to wonder if it wasn't a constant diameter. Turns out I was right.

The Matsumo idler from onlineautoparts.com.au wasn't perfectly cylindrical. There was 0.25mm variation over the width. This means the pulley is essentially conical and tries to turn the belt out of plane.

I put the original (worn out with noisy bearing) back on and the cold start belt squeal has gone away.



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[pneumatic]

This was the gates belt, maybe 2000km?



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